02343nas a2200217 4500008004100000245011300041210006900154260001200223490000700235520161700242653001501859653001301874653001401887653001701901653001001918100002401928700002901952700001601981700003301997856009502030 2024 eng d00aAntarctic lake viromes reveal potential virus associated influences on nutrient cycling in ice-covered lakes0 aAntarctic lake viromes reveal potential virus associated influen c09/20240 v153 a

The McMurdo Dry Valleys (MDVs) of Antarctica are a mosaic of extreme habitats which are dominated by microbial life. The MDVs include glacial melt holes, streams, lakes, and soils, which are interconnected through the transfer of energy and flux of inorganic and organic material via wind and hydrology. For the first time, we provide new data on the viral community structure and function in the MDVs through metagenomics of the planktonic and benthic mat communities of Lakes Bonney and Fryxell. Viral taxonomic diversity was compared across lakes and ecological function was investigated by characterizing auxiliary metabolic genes (AMGs) and predicting viral hosts. Our data suggest that viral communities differed between the lakes and among sites: these differences were connected to microbial host communities. AMGs were associated with the potential augmentation of multiple biogeochemical processes in host, most notably with phosphorus acquisition, organic nitrogen acquisition, sulfur oxidation, and photosynthesis. Viral genome abundances containing AMGs differed between the lakes and microbial mats, indicating site specialization. Using procrustes analysis, we also identified significant coupling between viral and bacterial communities (p = 0.001). Finally, host predictions indicate viral host preference among the assembled viromes. Collectively, our data show that: (i) viruses are uniquely distributed through the McMurdo Dry Valley lakes, (ii) their AMGs can contribute to overcoming host nutrient limitation and, (iii) viral and bacterial MDV communities are tightly coupled.

10aAntarctica10abacteria10alimnology10ametagenomics10avirus1 aRobinson, David, M.1 aMorgan-Kiss, Rachael, M.1 aWang, Zhong1 aTakacs-Vesbach, Cristina, D. uhttps://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1422941/full01464nas a2200181 4500008004100000022001400041245014100055210006900196260001200265520082200277653002101099653002001120653002301140653001801163653001001181100002901191856006201220 2024 eng d a0028-646X00aLong days and long nights: An integrative study reveals survival strategies of an Antarctic diatom during the cold and dark polar winter0 aLong days and long nights An integrative study reveals survival  c01/20243 a

The vast majority of photosynthetic organisms on Earth have evolved under a circadian cycle, with many cellular processes being regulated by the predictable patterns of day and night. Polar algal species living in Arctic and Antarctic aquatic habitats are faced with bizarre light environments of continuous light during the short summer months and 24-h darkness during the winter, that is one long day transitioning into one long, cold night. It is well known that polar phytoplankton survive the winter and return in the summer to form blooms. In an article recently published in New Phytologist, Joli et al. (2023, doi: 10.1111/nph.19387) use an integrative approach to dissect how an Antarctic marine diatom not only survives the long, dark polar winter, but also recovers rapidly upon the onset of summer.

10aaquatic habitats10acircadian cycle10alight environments10aphytoplankton10apolar1 aMorgan-Kiss, Rachael, M. uhttps://nph.onlinelibrary.wiley.com/doi/10.1111/nph.1953602587nas a2200313 4500008004100000022001400041245012700055210006900182260001200251300001100263520145800274653001701732653001401749653000801763653001901771653001501790100002301805700001801828700001501846700002401861700002501885700003301910700002901943700001701972700002201989700002102011700002102032856022002053 2024 eng d a0954-102000aMcMurdo Dry Valley lake edge ‘moats’: The ecological intersection between terrestrial and aquatic polar desert habitat0 aMcMurdo Dry Valley lake edge moats The ecological intersection b c04/2024 a1 - 173 a

Aquatic ecosystems - lakes, ponds and streams - are hotspots of biodiversity in the cold and arid environment of Continental Antarctica. Environmental change is expected to increasingly alter Antarctic aquatic ecosystems and modify the physical characteristics and interactions within the habitats that they support. Here, we describe physical and biological features of the peripheral ‘moat’ of a closed-basin Antarctic lake. These moats mediate connectivity amongst streams, lake and soils. We highlight the cyclical moat transition from a frozen winter state to an active open-water summer system, through refreeze as winter returns. Summer melting begins at the lakebed, initially creating an ice-constrained lens of liquid water in November, which swiftly progresses upwards, creating open water in December. Conversely, freezing progresses slowly from the water surface downwards, with water at 1 m bottom depth remaining liquid until May. Moats support productive, diverse benthic communities that are taxonomically distinct from those under the adjacent permanent lake ice. We show how ion ratios suggest that summer exchange occurs amongst moats, streams, soils and sub-ice lake water, perhaps facilitated by within-moat density-driven convection. Moats occupy a small but dynamic area of lake habitat, are disproportionately affected by recent lake-level rises and may thus be particularly vulnerable to hydrological change.

10aconnectivity10aecosystem10aice10amicrobial mats10atransition1 aStone, Michael, S.1 aDevlin, Shawn1 aHawes, Ian1 aWelch, Kathleen, A.1 aGooseff, Michael, N.1 aTakacs-Vesbach, Cristina, D.1 aMorgan-Kiss, Rachael, M.1 aAdams, Byron1 aBarrett, John, E.1 aPriscu, John, C.1 aDoran, Peter, T. uhttps://www.cambridge.org/core/journals/antarctic-science/article/mcmurdo-dry-valley-lake-edge-moats-the-ecological-intersection-between-terrestrial-and-aquatic-polar-desert-habitats/31D94DD51E651603482A3AE6E8A52A5702270nas a2200229 4500008004100000245011800041210006900159260001200228300000900240490000700249520153800256653002501794653002501819653001701844653002201861653002001883100001801903700002301921700002101944700002901965856004601994 2024 eng d00aPermanent stress adaptation and unexpected high light tolerance in the shade-adapted Chlamydomonas priscui0 aPermanent stress adaptation and unexpected high light tolerance  c08/2024 a22540 v133 a

The Antarctic photopsychrophile, Chlamydomonas priscui UWO241, is adapted to extreme environmental conditions, including permanent low temperatures, high salt, and shade. During long-term exposure to this extreme habitat, UWO241 appears to have lost several short-term mechanisms in favor of constitutive protection against environmental stress. This study investigated the physiological and growth responses of UWO241 to high-light conditions, evaluating the impacts of long-term acclimation to high light, low temperature, and high salinity on its ability to manage short-term photoinhibition. We found that UWO241 significantly increased its growth rate and photosynthetic activity at growth irradiances far exceeding native light conditions. Furthermore, UWO241 exhibited robust protection against short-term photoinhibition, particularly in photosystem I. Lastly, pre-acclimation to high light or low temperatures, but not high salinity, enhanced photoinhibition tolerance. These findings extend our understanding of stress tolerance in extremophilic algae. In the past 2 decades, climate change-related increasing glacial stream flow has perturbed long-term stable conditions, which has been associated with lake level rise, the thinning of ice covers, and the expansion of ice-free perimeters, leading to perturbations in light and salinity conditions. Our findings have implications for phytoplankton survival and the response to change scenarios in the light-limited environment of Antarctic ice-covered lakes.

10aCyclic electron flow10aenvironmental change10aextremophile10aphoto-acclimation10aphotoinhibition1 aPopson, Devon1 aD’Silva, Susanna1 aWheeless, Kaylie1 aMorgan-Kiss, Rachael, M. uhttps://www.mdpi.com/2223-7747/13/16/225402559nas a2200301 4500008004100000245008000041210006900121260001200190300001200202490000700214520166000221653001501881653001601896653002901912653001801941653001201959100002901971700001802000700002202018700002002040700002202060700001202082700001602094700002602110700002102136700003302157856006702190 2024 eng d00aSentinel protist taxa of the McMurdo Dry Valley lakes, Antarctica: A review0 aSentinel protist taxa of the McMurdo Dry Valley lakes Antarctica c03/2024 a13234720 v123 a

High-latitude meromictic lakes such as those in the Antarctic McMurdo Dry Valleys (MDV) harbor aquatic ecosystems dominated by the microbial loop. Within this habitat, which is limited year-round by light and nutrients, protists, or single celled eukaryotes, play outsized roles in the food web as the dominant primary producers and the apex predators. Thus, the MDV lake ecosystem represents an ideal system to study the role of sentinel protist taxa in carbon and nutrient cycling. The perennially ice-covered lakes are part of the McMurdo Long Term Ecological Research (McM LTER; mcmlter.org) established in 1993. In this review we will highlight the diversity and trophic roles of the MDV lake protist community and compare environmental factors driving spatiotemporal patterns in key protist taxa in two lakes within the McM LTER, Lakes Bonney and Fryxell. We will then discuss lessons learned from manipulated experiments on the impact of current and future climate-driven environmental change on sensitive protist taxa. Last, we will integrate knowledge gained from 25 years of lab-controlled experiments on key photosynthetic protists to extend our understanding of the function of these extremophiles within the MDV aquatic food webs. Our research group has studied the distribution and function of the MDV microbial community for nearly two decades, training the next generation of scientists to tackle future problems of these globally significant microbes. This review article will also highlight early career scientists who have contributed to this body of work and represent the future of scientific understanding in the Anthropocene.

10aAntarctica10aDisturbance10aMcMurdo Dry Valley lakes10aphytoplankton10aprotist1 aMorgan-Kiss, Rachael, M.1 aPopson, Devon1 aPereira, Rochelle1 aDolhi-Binder, J1 aTeufel, Amber, G.1 aLi, Wei1 aKalra, Isha1 aSherwell, Shasten, S.1 aReynebeau, Emily1 aTakacs-Vesbach, Cristina, D. uhttps://www.frontiersin.org/articles/10.3389/fevo.2024.132347202098nas a2200265 4500008004100000022001400041245010400055210006900159260001200228300001200240490000800252520131200260653001601572653001501588653001801603653002501621653002101646653001301667653002201680100001601702700001401718700001401732700002901746856005701775 2023 eng d a0166-859500aHigh salt-induced PSI-supercomplex is associated with high CEF and attenuation of state transitions0 aHigh saltinduced PSIsupercomplex is associated with high CEF and c09/2023 a65 - 840 v1573 a

While PSI-driven cyclic electron flow (CEF) and assembly of thylakoid supercomplexes have been described in model organisms like Chlamydomonas reinhardtii, open questions remain regarding their contributions to survival under long-term stress. The Antarctic halophyte, C. priscuii UWO241 (UWO241), possesses constitutive high CEF rates and a stable PSI-supercomplex as a consequence of adaptation to permanent low temperatures and high salinity. To understand whether CEF represents a broader acclimation strategy to short- and long-term stress, we compared high salt acclimation between the halotolerant UWO241, the salt-sensitive model, C. reinhardtii, and a moderately halotolerant Antarctic green alga, C. sp. ICE-MDV (ICE-MDV). CEF was activated under high salt and associated with increased non-photochemical quenching in all three Chlamydomonas species. Furthermore, high salt-acclimated cells of either strain formed a PSI-supercomplex, while state transition capacity was attenuated. How the CEF-associated PSI-supercomplex interferes with state transition response is not yet known. We present a model for interaction between PSI-supercomplex formation, state transitions, and the important role of CEF for survival during long-term exposure to high salt.

10aacclimation10aAntarctica10aChlamydomonas10aCyclic electron flow10aPSI-supercomplex10asalinity10astate transitions1 aKalra, Isha1 aWang, Xin1 aZhang, Ru1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/10.1007/s11120-023-01032-y01137nas a2200193 4500008004100000245005600041210005300097260001200150300001100162490000700173520056500180100002100745700001800766700001400784700002300798700002900821700002600850856006700876 2022 eng d00aAn Antarctic alga that can survive the extreme cold0 aAntarctic alga that can survive the extreme cold c05/2022 a7408380 v103 a

Microscopic algae are tougher than you might think. Some can even survive the extreme cold. In this article, we describe one of the coolest algae of all, the Antarctic green alga called Chlamydomonas sp. UWO241. This one-celled super-organism lives deep in the frigid waters of a remote and permanently ice-covered lake in Antarctica. How does this little alga thrive in such a barren and unwelcoming place? Well, dive into this article to learn how studying the genome of UWO241 is helping scientists better understand this amazingly hardy alga.

1 aSmith, David, R.1 aLeung, Arthur1 aZhang, Xi1 aCvetkovska, Marina1 aMorgan-Kiss, Rachael, M.1 aHüner, Norman, P. A. uhttps://kids.frontiersin.org/articles/10.3389/frym.2022.74083802039nas a2200169 4500008004100000245013000041210007100171260001200242520142300254100002601677700001601703700001201719700002401731700002101755700002901776856006401805 2022 eng d00aAntarctic lake phytoplankton and bacteria from near‐surface waters exhibit high sensitivity to climate‐driven disturbance0 aAntarctic lake phytoplankton and bacteria from near‐surface wate c07/20223 a

The McMurdo Dry Valleys (MDVs), Antarctica, represent a cold, desert ecosystem poised on the threshold of melting and freezing water. The MDVs have experienced dramatic signs of climatic change, most notably a warm austral summer in 2001–2002 that caused widespread flooding, partial ice cover loss and lake level rise. To understand the impact of these climatic disturbances on lake microbial communities, we simulated lake level rise and ice-cover loss by transplanting dialysis-bagged communities from selected depths to other locations in the water column or to an open water perimeter moat. Bacteria and eukaryote communities residing in the surface waters (5 m) exhibited shifts in community composition when exposed to either disturbance, while microbial communities from below the surface were largely unaffected by the transplant. We also observed an accumulation of labile dissolved organic carbon in the transplanted surface communities. In addition, there were taxa-specific sensitivities: cryptophytes and Actinobacteria were highly sensitive particularly to the moat transplant, while chlorophytes and several bacterial taxa increased in relative abundance or were unaffected. Our results reveal that future climate-driven disturbances will likely undermine the stability and productivity of MDV lake phytoplankton and bacterial communities in the surface waters of this extreme environment.

1 aSherwell, Shasten, S.1 aKalra, Isha1 aLi, Wei1 aMcKnight, Diane, M.1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttps://onlinelibrary.wiley.com/doi/10.1111/1462-2920.1611302206nas a2200229 4500008004100000022001400041245015000055210006900205260001200274300001400286490000700300520141400307653001801721653001501739653001801754100002101772700001601793700001901809700002901828700002601857856009301883 2022 eng d a0954-102000aAntibiotic resistance genes and taxa analysis from mat and planktonic microbiomes of Antarctic perennial ice-covered Lake Fryxell and Lake Bonney0 aAntibiotic resistance genes and taxa analysis from mat and plank c12/2022 a408 - 4220 v343 a

The perennial ice-covered lakes of the Antarctic McMurdo Dry Valleys harbour oligotrophic microbial communities that are separated geographically from other aquatic systems. Their microbiomes include planktonic microbes as well as lift-off mat communities that emerge from the ice. We used the ShortBRED protein family profiler to quantify the antibiotic resistance genes (ARGs) from metagenomes of lift-off mats emerging from ice and from filtered water samples of Lake Fryxell and Lake Bonney. The overall proportion of ARG hits was similar to that found in temperate-zone rural ponds with moderate human inputs. Specific ARGs showed distinct distributions for the two lakes and for mat vs planktonic sources. Metagenomic taxa distributions showed that mat phototrophs consisted mainly of cyanobacteria or Betaproteobacteria, whereas the water column phototrophs were mainly protists. An enrichment culture of the Betaproteobacterium Rhodoferax antarcticus from a Lake Fryxell mat sample showed an unusual mat-forming phenotype not previously reported for this species. Its genome showed no ARGs associated with Betaproteobacteria but had ARGs consistent with a minor Pseudomonas component. The Antarctic lake mats and water showed specific ARGs distinctive to the mat and water sources, but overall ARG levels were similar to those of temperate water bodies with moderate human inputs.

10amicrobial mat10aRhodoferax10aTaylor Valley1 aTallada, Sheetal1 aHall, Grant1 aBarich, Daniel1 aMorgan-Kiss, Rachael, M.1 aSlonczewski, Joan, L. uhttps://www.cambridge.org/core/product/identifier/S0954102022000360/type/journal_article02454nas a2200277 4500008004100000245020000041210006900241260001200310300001400322490000800336520152000344653001501864653001401879653002501893653001801918653001701936653000801953100002401961700001601985700002102001700001902022700001802041700002302059700002902082856006502111 2022 eng d00aCyclic electron flow (CEF) and ascorbate pathway activity provide constitutive photoprotection for the photopsychrophile, Chlamydomonas sp. UWO 241 (renamed Chlamydomonas priscuii)0 aCyclic electron flow CEF and ascorbate pathway activity provide  c03/2022 a235 - 2500 v1513 a

Under environmental stress, plants and algae employ a variety of strategies to protect the photosynthetic apparatus and maintain photostasis. To date, most studies on stress acclimation have focused on model organisms which possess limited to no tolerance to stressful extremes. We studied the ability of the Antarctic alga Chlamydomonas sp. UWO 241 (UWO 241) to acclimate to low temperature, high salinity or high light. UWO 241 maintained robust growth and photosynthetic activity at levels of temperature (2 °C) and salinity (700 mM NaCl) which were nonpermissive for a mesophilic sister species, Chlamydomonas raudensis SAG 49.72 (SAG 49.72). Acclimation in the mesophile involved classic mechanisms, including downregulation of light harvesting and shifts in excitation energy between photosystem I and II. In contrast, UWO 241 exhibited high rates of PSI-driven cyclic electron flow (CEF) and a larger capacity for nonphotochemical quenching (NPQ). Furthermore, UWO 241 exhibited constitutively high activity of two key ascorbate cycle enzymes, ascorbate peroxidase and glutathione reductase and maintained a large ascorbate pool. These results matched the ability of the psychrophile to maintain low ROS under short-term photoinhibition conditions. We conclude that tight control over photostasis and ROS levels are essential for photosynthetic life to flourish in a native habitat of permanent photooxidative stress. We propose to rename this organism Chlamydomonas priscuii.

10aAntarctica10aascorbate10aCyclic electron flow10aPhotosystem I10aPsychrophile10aROS1 aStahl-Rommel, Sarah1 aKalra, Isha1 aD'Silva, Susanna1 aHahn, Mark, M.1 aPopson, Devon1 aCvetkovska, Marina1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/article/10.1007/s11120-021-00877-503572nas a2200301 4500008004100000245010000041210006900141260001200210300001100222490000800233520264300241653002302884653001002907653002002917653002202937653002602959653001902985653001603004100002603020700002103046700002303067700001403090700002603104700002303130700001603153700002903169856007203198 2022 eng d00aPhotosynthetic adaptation to polar life: Energy balance, photoprotection and genetic redundancy0 aPhotosynthetic adaptation to polar life Energy balance photoprot c01/2022 a1535570 v2683 a

The persistent low temperature that characterize polar habitats combined with the requirement for light for all photoautotrophs creates a conundrum. The absorption of too much light at low temperature can cause an energy imbalance that decreases photosynthetic performance that has a negative impact on growth and can affect long-term survival. The goal of this review is to survey the mechanism(s) by which polar photoautotrophs maintain cellular energy balance, that is, photostasis to overcome the potential for cellular energy imbalance in their low temperature environments. Photopsychrophiles are photosynthetic organisms that are obligately adapted to low temperature (0-15 °C) but usually die at higher temperatures (≥20 °C). In contrast, photopsychrotolerant species can usually tolerate and survive a broad range of temperatures (5-40 °C). First, we summarize the basic concepts of excess excitation energy, energy balance, photoprotection and photostasis and their importance to survival in polar habitats. Second, we compare the photoprotective mechanisms that underlie photostasis and survival in aquatic cyanobacteria and green algae as well as terrestrial Antarctic and Arctic plants. We show that polar photopsychrophilic and photopsychrotolerant organisms attain energy balance at low temperature either through a regulated reduction in the efficiency of light absorption or through enhanced capacity to consume photosynthetic electrons by the induction of O2 as an alternative electron acceptor. Finally, we compare the published genomes of three photopsychrophilic and one photopsychrotolerant alga with five mesophilic green algae including the model green alga, Chlamydomonas reinhardtii. We relate our genomic analyses to photoprotective mechanisms that contribute to the potential attainment of photostasis. Finally, we discuss how the observed genomic redundancy in photopsychrophilic genomes may confer energy balance, photoprotection and resilience to their harsh polar environment. Primary production in aquatic, Antarctic and Arctic environments is dependent on diverse algal and cyanobacterial communities. Although mosses and lichens dominate the Antarctic terrestrial landscape, only two extant angiosperms exist in the Antarctic. The identification of a single ‘molecular key’ to unravel adaptation of photopsychrophily and photopsychrotolerance remains elusive. Since these photoautotrophs represent excellent biomarkers to assess the impact of global warming on polar ecosystems, increased study of these polar photoautotrophs remains essential.

10agenomic redundancy10alight10aphotoprotection10aphotopsychrophily10aphotopsychrotolerance10aPhotosynthesis10atemperature1 aHüner, Norman, P. A.1 aSmith, David, R.1 aCvetkovska, Marina1 aZhang, Xi1 aIvanov, Alexander, G.1 aSzyszka-Mroz, Beth1 aKalra, Isha1 aMorgan-Kiss, Rachael, M. uhttps://www.sciencedirect.com/science/article/pii/S017616172100196601659nas a2200193 4500008004100000022001300041245008600054210006900140260001200209300001100221490000700232520104000239100001401279700002301293700002901316700002601345700002201371856007201393 2021 eng d a2589004200aDraft genome sequence of the Antarctic green alga Chlamydomonas sp. UWO2410 aDraft genome sequence of the Antarctic green alga IChlamydomonas c2021-02 a1020840 v243 a

Antarctica is home to an assortment of psychrophilic algae, which have evolved various survival strategies for coping with their frigid environments. Here, we explore Antarctic psychrophily by examining the ∼212 Mb draft nuclear genome of the green alga Chlamydomonas sp. UWO241, which resides within the water column of a perennially ice-covered, hypersaline lake. Like certain other Antarctic algae, UWO241 encodes a large number (≥37) of ice-binding proteins, putatively originating from horizontal gene transfer. Even more striking, UWO241 harbors hundreds of highly similar duplicated genes involved in diverse cellular processes, some of which we argue are aiding its survival in the Antarctic via gene dosage. Gene and partial gene duplication appear to be an ongoing phenomenon within UWO241, one which might be mediated by retrotransposons. Ultimately, we consider how such a process could be associated with adaptation to extreme environments but explore potential non-adaptive hypotheses as well.

1 aZhang, Xi1 aCvetkovska, Marina1 aMorgan-Kiss, Rachael, M.1 aHüner, Norman, P. A.1 aSmith, David, Roy uhttps://www.sciencedirect.com/science/article/pii/S258900422100052303475nas a2200217 4500008004100000245017000041210006900211260003900280300000800319490000800327520273200335653001603067653000803083653001703091653001903108653002003127653001703147100001603164700002903180856004803209 2021 eng d00aRole of cyclic electron flow (CEF) and photosystem I (PSI) supercomplex formation during acclimation to long-term salinity stress in green algae: A comparative study0 aRole of cyclic electron flow CEF and photosystem I PSI supercomp aOxford, OHbMiami Universityc2021 a2360 vPhD3 aPhotosynthesis is one of the most important processes on Earth by which organisms convert solar energy into usable forms of energy. Linear electron flow (LEF) and cyclic electron flow (CEF) constitute two major pathways in photosynthesis. While LEF leads to production of both ATP and NADPH, CEF only produces ATP that helps balance the ATP:NADPH ratio required for carbon fixation. CEF also plays a major role during acclimation to several environmental stressors. However, the regulation and mechanism by which CEF operates is still not clearly understood. Recent studies have shown that formation of a protein supercomplex with PSI appears to be essential for induction of CEF in several model organisms. However, both supercomplex formation and CEF induction have been mainly studied under short-term, transitory stress conditions. In addition, the role and mechanism by which organisms may rely on CEF to survive in their natural habitat and acclimate to stress over a long period of time has not been considered. In this study we compared how three photosynthetic organisms (one model alga, Chlamydomonas reinhardtii; two extremophiles, C. sp. UWO241 and C. sp. ICE-MDV) utilize CEF to cope with their natural environment and adapt to steady-state environmental stress. To that end, the objectives of this thesis were i) to elucidate the role of CEF in long-term salinity acclimation ii) to understand the downstream changes associated with increased CEF, and iii) to identify whether PSI-supercomplexes are associated with increased CEF during salinity acclimation. We hypothesized that a stable PSI-supercomplex is required for high CEF, which in turn supports strong carbon fixation capacity for production of downstream metabolic products important for long-term acclimation to salinity stress. We showed for the first time, that increased CEF in UWO241 leads to excess ATP production and rewiring of downstream metabolism under high salinity. Next, we showed that a laboratory evolved salinity-tolerant strain of model C. reinhardtii uses constitutive upregulation of CEF to deal with salinity stress, which is in-turn associated with increased non-photochemical quenching and rewired carbon metabolism. Last, we show that CEF is involved in salinity acclimation in all three Chlamydomonas species, regardless of their salinity tolerance. We also show that PSI-supercomplexes are associated with increased CEF in these species. Characterization of high-salt supercomplex of C. reinhardtii revealed that it shares many similarities with the extensively described state 2 supercomplex, and that supercomplex composition might be species dependent rather than stress dependent.10aacclimation10aCEF10aextremophile10aPhotosynthesis10asalinity stress10asupercomplex1 aKalra, Isha1 aMorgan-Kiss, Rachael, M. uhttps://www.proquest.com/docview/257256058502753nas a2200325 4500008004100000022001400041245011500055210007300170260001200243300001800255490000800273520178400281653001002065653001402075653001602089653000802105653001002113653001002123653001402133653001102147100002802158700002102186700003302207700002202240700002202262700002402284700002902308700002102337856006902358 2021 eng d a2169-895300aYear‐round and long‐term phytoplankton dynamics in Lake Bonney, a permanently ice‐covered Antarctic lake0 aYear‐round and long‐term phytoplankton dynamics in Lake Bonney a c04/2021 ae2020JG0059250 v1263 a

Lake Bonney (McMurdo Dry Valleys, east Antarctica) represents a year‐round refugium for life adapted to permanent extreme conditions. Despite intensive research since the 1960s, due to the logistical constraints posed by 4‐months of 24‐h darkness, knowledge of how the resident photosynthetic microorganisms respond to the polar winter is limited. In addition, the lake level has risen by more than 3 m since 2004: impacts of rapid lake level rise on phytoplankton community structure is also poorly understood. From 2004 to 2015 an in situ submersible spectrofluorometer (bbe FluoroProbe) was deployed in Lake Bonney during the austral summer to quantify the vertical structure of four functional algal groups (green algae, mixed algae, and cryptophytes, cyanobacteria). During the 2013–2014 field season the Fluoroprobe was mounted on autonomous cable‐crawling profilers deployed in both the east and west lobes of Lake Bonney, obtaining the first daily phytoplankton profiles through the polar night. Our findings showed that phytoplankton communities were differentially impacted by physical and chemical factors over long‐term versus seasonal time scales. Following a summer of rapid lake level rise (2010–2011), an increase in depth integrated chlorophyll a (chl‐a) occurred in Lake Bonney caused by stimulation of photoautotrophic green algae. Conversely, peaks in chl‐a during the polar night were associated with an increase in mixotrophic haptophytes and cryptophytes. Collectively our data reveal that phytoplankton groups possessing variable trophic abilities are differentially competitive during seasonal and long‐term time scales owing to periods of higher nutrients (photoautotrophs) versus light/energy limitation (mixotrophs).

10aalgae10aAntarctic10afluorometry10aice10alakes10alight10aprofiling10awinter1 aPatriarche, Jeffrey, D.1 aPriscu, John, C.1 aTakacs-Vesbach, Cristina, D.1 aWinslow, Luke, A.1 aMyers, Krista, F.1 aBuelow, Heather, N.1 aMorgan-Kiss, Rachael, M.1 aDoran, Peter, T. uhttps://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JG00592502207nas a2200205 4500008004100000245010800041210006900149260001200218520152500230100001601755700001401771700002301785700001901808700002201827700001401849700001901863700002101882700002901903856006901932 2020 eng d00aChlamydomonas sp. UWO 241 exhibits high cyclic electron flow and rewired metabolism under high salinity0 aChlamydomonas sp UWO 241 exhibits high cyclic electron flow and  c03/20203 a

The Antarctic green alga Chlamydomonas sp. UWO 241 (UWO 241) is adapted to permanent low temperatures, hypersalinity, and extreme shade. one of the most striking phenotypes of UWO 241 is an altered photosystem I (PSI) organization and constitutive PSI cyclic electron flow (CEF). To date, little attention has been paid to CEF during long-term stress acclimation, and the consequences of sustained CEF in UWO 241 are not known. In this study, we combined photobiology, proteomics, and metabolomics to understand the underlying role of sustained CEF in high salinity stress acclimation. High salt-grown UWO 241 exhibited increased thylakoid proton motive flux and an increased capacity for non-photochemical quenching. Under high salt, a significant proportion of the upregulated enzymes were associated with the Calvin Benson Bassham Cycle, carbon storage metabolism, and protein translation. Two key enzymes of the Shikimate pathway, DAHP synthase and chorismate synthase, were also upregulated, as well as indole-3-glycerol phosphate synthase, an enzyme involved in the biosynthesis of L-tryptophan and indole acetic acid. In addition, several compatible solutes (glycerol, proline, and sucrose) accumulated to high levels in high salt-grown UWO 241 cultures. We suggest that UWO 241 maintains constitutively high CEF through the associated PSI-cytochrome b6f supercomplex to support robust growth and strong photosynthetic capacity under a constant growth regime of low temperatures and high salinity.

1 aKalra, Isha1 aWang, Xin1 aCvetkovska, Marina1 aJeong, Jooyeon1 aMcHargue, William1 aZhang, Ru1 aHüner, Norman1 aYuan, Joshua, S.1 aMorgan-Kiss, Rachael, M. uhttp://www.plantphysiol.org/content/early/2020/04/03/pp.19.0128002015nas a2200217 4500008004100000245016100041210006900202260001200271490000700283520122000290653001501510653001801525653002301543653003901566653001601605653003001621100002301651700002901674700002401703856007001727 2020 eng d00aGlycerol is an osmoprotectant in two Antarctic Chlamydomonas species from an ice-covered saline lake and is synthesized by an unusual bidomain enzyme0 aGlycerol is an osmoprotectant in two Antarctic IChlamydomonasI s c08/20200 v113 a

Glycerol, a compatible solute, has previously been found to act as an osmoprotectant in some marine Chlamydomonas species and several species of Dunaliella from hypersaline ponds. Recently, Chlamydomonas reinhardtii and Dunaliella salina were shown to make glycerol with an unusual bidomain enzyme, which appears to be unique to algae, that contains a phosphoserine phosphatase and glycerol-3-phosphate dehydrogenase. Here we report that two psychrophilic species of Chlamydomonas (C. spp. UWO241 and ICE-MDV) from Lake Bonney, Antarctica also produce high levels of glycerol to survive in the lake’s saline waters. Glycerol concentration increased linearly with salinity and at 1.3 M NaCl, exceeded 400 mM in C. sp. UWO241, the more salt-tolerant strain. We also show that both species expressed several isoforms of the bidomain enzyme. An analysis of one of the isoforms of C. sp. UWO241 showed that it was strongly upregulated by NaCl and is thus the likely source of glycerol. These results reveal another adaptation of the Lake Bonney Chlamydomonas species that allow them to survive in an extreme polar environment.

10aAntarctica10aChlamydomonas10aglycerol synthesis10aglycerol-3-phosphate dehydrogenase10aLake Bonney10aphosphoserine phosphatase1 aRaymond, James, A.1 aMorgan-Kiss, Rachael, M.1 aStahl-Rommel, Sarah uhttps://www.frontiersin.org/articles/10.3389/fpls.2020.01259/full02448nas a2200217 4500008004100000245010000041210006900141260001200210490000700222520174400229100001201973700001901985700002702004700002102031700001602052700001702068700002902085700002302114700002102137856007202158 2020 eng d00aMethane production in the oxygenated water column of a perennially ice‐covered Antarctic lake0 aMethane production in the oxygenated water column of a perennial c01/20200 v653 a

Aerobic methane production in aquatic ecosystems impacts the global atmospheric budget of methane, but the extent, mechanism, and taxa responsible for producing this greenhouse gas are not fully understood. Lake Bonney (LB), a perennially ice‐covered Antarctic lake, has cold hypersaline waters underlying an oxygenated freshwater layer. We present temporal methane concentration profiles in LB indicating methane production in the oxygenated (> 200% air saturation) water. Experiments amended with methylphosphonate (MPn) yielded methane generation, suggesting in situ methanogenesis via the carbon‐phosphorus (C‐P) lyase pathway. Enrichment cultures from the lake were used to isolate five bacterial strains capable of generating methane when supplied with MPn as the sole P source. Based on 16S rRNA gene sequencing, the isolates belong to the Proteobacteria (closely related to Marinomonas, Hoeflea, and Marinobacter genera) and Bacteroidetes (Algoriphagus genus). 16S rRNA metagenomic sequencing confirms the presence of these taxa in LB. None of the isolated species were reported to be capable to produce methane. In addition, orthologs of the phosphoenolpyruvate mutase gene (PepM) and methylphosphonate synthase (MPnS), enzymes involved in phosphonate and MPn biosynthesis, were widely spread in the LB shotgun metagenomic libraries; genes related to C‐P lyase pathways (phn gene clusters) were also abundant. 16S rRNA and mcrA genes of anaerobic methanogens were absent in both 16S rRNA and metagenomics libraries. These data reveal that in situ aerobic biological methane production is likely a significant source of methane in LB.

1 aLi, Wei1 aDore, John, E.1 aSteigmeyer, August, J.1 aCho, Yong‐Joon1 aKim, Ok-Sun1 aLiu, Yongqin1 aMorgan-Kiss, Rachael, M.1 aSkidmore, Mark, L.1 aPriscu, John, C. uhttps://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.1125701902nas a2200181 4500008004100000245011100041210006900152260003900221490000900260520124000269653001901509653002401528653002601552653001801578100002601596700002901622856006901651 2020 eng d00aResponse of microbial communities to climatic disturbances in Lake Bonney, McMurdo Dry Valleys, Antarctica0 aResponse of microbial communities to climatic disturbances in La aOxford, OHbMiami Universityc20200 vM.S.3 a

The McMurdo Dry Valleys is a polar desert ecosystem which composes the largest ice-free area in Antarctica, with the exception of perennially ice-covered lakes and ponds. The lakes in the valleys are the only landscape unit that support metabolic activity year-round. Recent increases in air temperature and solar radiation have led to a chain of disturbances altering the environmental conditions of these lakes. In this study, we test the impact of climatic disturbances on microbial communities in Lake Bonney, one of the lakes in the MDV. Through an integrated approach of combining field studies on natural communities in the lake (in situ) and laboratory experiments on algal isolates (ex situ), this study will attempt to understand how phytoplankton, eukaryal and bacterial communities respond to simulated disturbances. Results from the in situ experiments showed that the moat is a unique and stressful environment for under-ice communities and that under-ice shallow communities are highly sensitive to climatic disturbances. The ex situ experiments showed that certain phytoplankton species, like the chlorophytes, are more resistant to environmental alterations and thus will outcompete other phytoplankton species.

10aclimate change10aMcMurdo Dry Valleys10amicrobial communities10aphytoplankton1 aSherwell, Shasten, S.1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami159595868836487702357nas a2200205 4500008004100000245012200041210006900163260001200232490000700244520163100251100002501882700002701907700001801934700002501952700002501977700002902002700002502031700002302056856007202079 2020 eng d00aVertical stratification and stability of biogeochemical processes in the deep saline waters of Lake Vanda, Antarctica0 aVertical stratification and stability of biogeochemical processe c03/20200 v653 a

Lake Vanda is a permanently ice-covered lake in the McMurdo Dry Valleys of Antarctica. Its bottom waters remain stratified year-round because of a strong salinity-driven density gradient. We have assessed spatial patterns in and relationships between major biogeochemical processes in the water column of Lake Vanda. Samples were collected in the austral summers of 2008 and 2011 to measure concentrations of metabolites associated with a suite of biogeochemical processes across the deep salinity gradient. The shapes of the resulting geochemical profiles were consistent between 2008 and 2011. Metabolite production and consumption rates were estimated using a reactive transport model based on the assumption that vertical diffusion was the only activephysical transport process. We validated this model for nitrification by using stable isotope incubations to show that this process was only active at depths predicted by the model. No nitrification activity was observed at 68 m depth in spite of overlapping oxygen and ammonium gradients. We attribute this lack of activity to the competitive inhibition of ammonia monooxygenase by methane. Net nitrous oxide and nitrate consumption were observed in the oxic water column, providing evidence of aerobic denitrification. The depth of maximum net oxygen production did not coincide with the deep chlorophyll maxima (at 59.3, 63, and 68.2 m) measured in the same profile. Finally, the integrated sulfide oxidation rate was high compared with other oxidation processes, indicating that sulfide was an important electron donor for the water column microbial community.

1 aSchutte, Charles, A.1 aSamarkin, Vladimir, A.1 aPeters, Brian1 aMadigan, Michael, T.1 aBowles, Marshall, W.1 aMorgan-Kiss, Rachael, M.1 aCasciotti, Karen, L.1 aJoye, Samantha, B. uhttps://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.1132702684nas a2200265 4500008004100000022001400041245014900055210006900204260001200273490000600285520185300291653001502144653002502159653000902184653001802193653001702211100001502228700001802243700001602261700001202277700001402289700002102303700002902324856006502353 2019 eng d a0166-859500aThe Antarctic psychrophiles Chlamydomonas spp. UWO241 and ICE-MDV exhibit differential restructuring of photosystem I in response to iron0 aAntarctic psychrophiles iChlamydomonasi spp UWO241 and ICEMDV ex c02/20190 v93 a

Chlamydomonas sp. UWO241 is a psychrophilic alga isolated from the deep photic zone of a perennially ice-covered Antarctic lake (east lobe Lake Bonney, ELB). Past studies have shown that C. sp. UWO241 exhibits constitutive downregulation of photosystem I (PSI) and high rates of PSI-associated cyclic electron flow (CEF). Iron levels in ELB are in the nanomolar range leading us to hypothesize that the unusual PSI phenotype of C. sp. UWO241 could be a response to chronic Fe-deficiency. We studied the impact of Fe availability in C. sp. UWO241, a mesophile, C. reinhardtii SAG11-32c, as well as a psychrophile isolated from the shallow photic zone of ELB, Chlamydomonas sp. ICE-MDV. Under Fe-deficiency, PsaA abundance and levels of photooxidizable P700 (ΔA820/A820) were reduced in both psychrophiles relative to the mesophile. Upon increasing Fe, C. sp. ICE-MDV and C. reinhardtii exhibited restoration of PSI function, while C. sp. UWO241 exhibited only moderate changes in PSI activity and lacked almost all LHCI proteins. Relative to Fe-excess conditions (200 μM Fe2+), C. sp. UWO241 grown in 18 μM Fe2+ exhibited downregulation of light harvesting and photosystem core proteins, as well as upregulation of a bestrophin-like anion channel protein and two CEF-associated proteins (NdsS, PGL1). Key enzymes of starch synthesis and shikimate biosynthesis were also upregulated. We conclude that in response to variable Fe availability, the psychrophile C. sp. UWO241 exhibits physiological plasticity which includes restructuring of the photo-chemical apparatus, increased PSI-associated CEF, and shifts in downstream carbon metabolism toward storage carbon and secondary stress metabolites.

10aAntarctica10aCyclic electron flow10aIron10aPhotosystem I10aPsychrophile1 aCook, Greg1 aTeufel, Amber1 aKalra, Isha1 aLi, Wei1 aWang, Xin1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/article/10.1007/s11120-019-00621-002939nas a2200241 4500008004100000245010800041210006900149260001200218300001100230490000800241520220100249653000902450653001602459653003202475653001302507653001302520100001602533700001802549700001402567700001502581700002902596856007202625 2019 eng d00aCommunity response of microbial primary producers to salinity is primarily driven by nutrients in lakes0 aCommunity response of microbial primary producers to salinity is c12/2019 a1340010 v6963 a

Higher microbial diversity was frequently observed in saline than fresh waters, but the underlying mechanisms remains unknown, particularly in microbial primary producers (MPP). MPP abundance and activity are notably constrained by high salinity, but facilitated by high nutrients. It remains to be ascertained whether and how nutrients regulate the salinity constraints on MPP abundance and community structure. Here we investigated the impact of nutrients on salinity constraints on MPP abundance and diversity in undisturbed lakes with a wide salinity range on the Tibetan Plateau. MPP community was explored using quantitative PCR, terminal restriction fragment length polymorphism and sequencing of cloning libraries targeting form IC cbbL gene. The MPP community structure was sorted by salinity into freshwater (salinity<1‰), saline (1‰ < salinity<29‰) and hypersaline (salinity>29‰) lakes. Furthermore, while MPP abundance, diversity and richness were significantly constrained with increasing salinity, these constraints were mitigated by enhancing total organic carbon (TOC) and total nitrogen (TN) contents in freshwater and saline lakes. In contrast, the MPP diversity increased significantly with the salinity in hypersaline lakes, due to the mitigation of enhancing TOC and TN contents and salt-tolerant MPP taxa. The mitigating effect of nutrients was more pronounced in saline than in freshwater and hypersaline lakes. The MPP compositions varied along salinity, with Betaproteobacteria dominating both the freshwater and saline lakes and Gammaproteobacteria dominating the hypersaline lakes. We concluded that high nutrients could mitigate the salinity constraining effects on MPP abundance, community richness and diversity. Our findings offer a novel insight into the salinity effects on primary producers and highlight the interactive effects of salinity and nutrients on MPP in lakes. These findings can be used as a baseline to illuminate the effects of increased anthropogenic activities altering nutrient dynamics on the global hydrological cycle and the subsequent responses thereof by MPP communities.

10acbbL10alake waters10amicrobial primary producers10anutrient10asalinity1 aYue, Linyan1 aKong, Weidong1 aJi, Mukan1 aLiu, Jinbo1 aMorgan-Kiss, Rachael, M. uhttps://www.sciencedirect.com/science/article/pii/S004896971933978602573nas a2200265 4500008004100000022001400041245010400055210006900159260001200228300001400240490000700254520177600261653002002037653002102057653001502078653001702093653002402110653001202134653002502146100001202171700002002183700001602203700002902219856005902248 2019 eng d a0948-305500aDrivers of protistan community autotrophy and heterotrophy in chemically stratified Antarctic lakes0 aDrivers of protistan community autotrophy and heterotrophy in ch c01/2019 a225 - 2390 v823 a

Single-celled, eukaryotic microorganisms, known as protists, are responsible for 2 important, yet opposing, metabolic activities within aquatic food webs. They are major primary producers and highly active predators in marine and fresh water systems. While genomics has accelerated in recent years for this taxonomically diverse group, our understanding of the metabolic capabilities of most protists remains limited. It is also poorly understood how protist trophic mode is affected by biotic and abiotic factors, and therefore it is difficult to predict how events such as global climate change will affect the balance between autotrophic and heterotrophic activities in protist communities. To address open questions regarding how protist metabolic versatility is influenced by their environment, we characterized the potential for carbon fixation versus organic carbon degradation using enzymatic assays (RubisCO and β-D-glucosaminidase, respectively) within the water columns of ice-covered lakes in McMurdo Dry Valleys (MDV), Antarctica. Steep physical and chemical gradients in the water columns, microorganism domination and minimal allochthonous inputs makes the MDV lakes uniquely suited to investigate environment-microbe interactions. Spatial trends in RubisCO and β-D-glucosaminidase activities were lake-specific and vertically stratified within the water columns. Moreover, bottom-up drivers controlling the activity of C-fixation vs. organic C-degradation among the MDV protist communities were distinct between the upper photic vs. the deep, aphotic zones. We conclude that differential controls over major C-cycling enzymes have important implications on the influence of environmental change on the carbon and nutrient cycles in the MDV lakes.

10aAntarctic lakes10aAquatic protists10aAutotrophy10aHeterotrophy10aMcMurdo Dry Valleys10aRubisCO10aβ-D-glucosaminidase1 aLi, Wei1 aDolhi-Binder, J1 aCariani, ZE1 aMorgan-Kiss, Rachael, M. uhttps://www.int-res.com/abstracts/ame/v82/n3/p225-239/02158nas a2200229 4500008004100000245010300041210006900144260003900213490000900252520137700261653001001638653002801648653003801676653002401714653001901738653001801757653002301775653001601798100001601814700002901830856006901859 2019 eng d00aImpact of simulated polar night on Antarctic mixotrophic and strict photoautotrophic phytoplankton0 aImpact of simulated polar night on Antarctic mixotrophic and str aOxford, OHbMiami Universityc20180 vM.S.3 a

Phytoplankton in polar regions experience long periods of continuous darkness annually during the polar night. Due to difficulties in performing field work during this period, it is largely unknown how phytoplankton endure this extreme transition from 24-hour daylight in the fall to several months of total darkness in the austral winter. The primary goal of this study was to compare physiological and photosynthetic responses of several Antarctic phytoplankton of variable trophic abilities (pure photosynthetic vs. mixotrophic) to simulated polar night conditions, including the transition seasons before and after winter. Two distinct responses were observed to extended darkness: (1) strict photoautotrophs (Chlamydomonas sp. ICE-MDV and Chlamydomonas sp. UWO241) exhibited functional downregulation their photosynthetic processes in the winter, followed by a lag phase of several days during mimicked spring, and (2) mixotrophs (Isochrysis sp. MDV and Geminigera cryophila) maintained functional photosynthetic apparatus, increased heterotrophy through the winter, and exhibited immediate growth upon return to light incubation. These differing responses to mimicked polar night conditions could represent two different strategies for surviving the long period of darkness in the phytoplankton’s natural environment.

10aalgae10aAntarctic phytoplankton10achlorophyll fluorescence analysis10aMcMurdo Dry Valleys10aPhotosynthesis10aphytoplankton10apolar microbiology10apolar night1 aCariani, ZE1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami154720459996908102372nas a2200193 4500008004100000245016100041210006900202260001200271490000700283520165600290653002101946653002601967653002701993653001702020653002902037100001202066700002902078856007102107 2019 eng d00aInfluence of environmental drivers and potential interactions on the distribution of microbial communities from three permanently stratified Antarctic lakes0 aInfluence of environmental drivers and potential interactions on c05/20190 v103 a

The McMurdo Dry Valley (MDV) lakes represent unique habitats in the microbial world. Perennial ice covers protect liquid water columns from either significant allochthonous inputs or seasonal mixing, resulting in centuries of stable biogeochemistry. Extreme environmental conditions including low seasonal photosynthetically active radiation (PAR), near freezing temperatures, and oligotrophy have precluded higher trophic levels from the food webs. Despite these limitations, diverse microbial life flourishes in the stratified water columns, including Archaea, bacteria, fungi, protists, and viruses. While a few recent studies have applied next generation sequencing, a thorough understanding of the MDV lake microbial diversity and community structure is currently lacking. Here we used Illumina MiSeq sequencing of the 16S and 18S rRNA genes combined with a microscopic survey of key eukaryotes to compare the community structure and potential interactions among the bacterial and eukaryal communities within the water columns of Lakes Bonney (east and west lobes, ELB, and WLB, respectively) and Fryxell (FRX). Communities were distinct between the upper, oxic layers and the dark, anoxic waters, particularly among the bacterial communities residing in WLB and FRX. Both eukaryal and bacterial community structure was influenced by different biogeochemical parameters in the oxic and anoxic zones. Bacteria formed complex interaction networks which were lake-specific. Several eukaryotes exhibit potential interactions with bacteria in ELB and WLB, while interactions between these groups in the more productive FRX were relatively rare.

10aAquatic protists10aenvironmental drivers10aheterotrophic bacteria10ainteractions10aMcMurdo Dry Valley lakes1 aLi, Wei1 aMorgan-Kiss, Rachael, M. uhttps://www.frontiersin.org/articles/10.3389/fmicb.2019.01067/full02006nas a2200133 4500008004100000245016300041210006900204260003900273490000900312520143800321100001501759700002901774856006901803 2018 eng d00aAntarctic Chlamydomonas strains C. sp. UWO241 and ICE-MDV exhibit differential restructuring of the photosynthetic apparatus in response to iron0 aAntarctic iChlamydomonasi strains iCi sp UWO241 and ICEMDV exhib aOxford, OHbMiami Universityc20180 vM.S.3 a

As an integral cofactor for many redox-associated processes, iron (Fe) homeostasis is crucial in order to produce sufficient energy for the organism. Fe limitation, or excess, can cause major alterations in the function and structure of the photosynthetic apparatus. Photosynthetic psychrophiles grown under permanent low temperatures exhibit novel adaptations in their photosynthetic apparatus to deal with this permanent stress. The ice-covered lakes of the McMurdo Dry Valleys harbor many species of cold-adapted algae, including Chlamydomonas sp. UWO241 (UWO241). As a consequence of adaptation to multiple permanent extreme conditions, UWO241 exhibits a remodeled photosynthetic apparatus for maintaining redox poise. One unusual characteristic of UWO241 is the absence of a PSI-associated 77K fluorescence emission under a wide range of growth conditions. This phenotype resembles Fe deficiency in other model organisms such as C. reinhardtii. We hypothesized that adaptation to permanent iron deficiency in its native environment may contribute to this unusual phenotype. We compared the effect of Fe availability on the physiology and photobiology of UWO241 with the model C. reinhardtii as well as a second psychrophilic alga, Chlamydomonas sp. ICE-MDV (ICE). The impacts of a restructured photosynthetic apparatus on the unique Fe-associated phenotype in UWO241 will be discussed.

1 aCook, Greg1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami152545562177883602179nas a2200121 4500008004100000245006300041210006300104260002600167520172200193100002201915700002901937856009101966 2018 eng d00aPhysiological and Biochemical Adaptations of Psychrophiles0 aPhysiological and Biochemical Adaptations of Psychrophiles aBoca RatonbCRC Press3 a

The cold biosphere encompasses many microorganism-dominated habitats that rely on light-dependent primary production. Within these environments, there are numerous physical and chemical factors limiting metabolism and growth that the microorganisms must overcome. The psychrophilic microorganisms discussed herein integrate a complex spectrum of adaptive strategies to survive these physiological challenges, including genome evolution, enzyme structure and catalysis rate changes, cryoprotectant formation, and a multitude of photosynthetic adaptations. Psychrophilic organisms also hold the key to biotechnical advances and the future, such that psychrophilic enzymes are used for everything from laboratory reagents and industrial work to medical research and environmental sustainability. Researchers have learned to exploit psychrophiles’ efficiency at low temperatures (i.e., cooler washing machines and energy-saving, cost-effective enzyme production), their higher energy activity (thus allowing lower concentrations of needed catalysts, reducing costs and procedure time), and their ability to contribute to hydrocarbon bioremediation. Although psychrophilic microbes exist in numerous habitats and undergo various adaptive strategies, an understanding of what makes an organism psychrophilic is still unknown in a large majority of cold-adapted organisms, and thus future investigations are needed regarding cold adaptation and their biotechnological potential. Even as research has increased over the last decade, new technological advances and high-throughput DNA sequencing will continue to provide information about cold adaptation or the mechanisms needed for survival in a changing world.

1 aTeufel, Amber, G.1 aMorgan-Kiss, Rachael, M. uhttps://www.taylorfrancis.com/books/e/9781498774932/chapters/10.1201%2F9781315154695-902691nas a2200229 4500008004100000022001400041245015500055210006900210260001200279490000700291520189400298653003402192653001902226653002402245653002202269653002302291100002202314700001202336700002002348700002902368856006402397 2017 eng d a0722-406000aImpact of nitrogen and phosphorus on phytoplankton production and bacterial community structure in two stratified Antarctic lakes: a bioassay approach0 aImpact of nitrogen and phosphorus on phytoplankton production an c05/20170 v403 a

Arctic, Antarctic, and alpine ecosystems are recognized as sensors and sentinels of global change. As a consequence of their high sensitivity to minor climatic perturbations, permanently ice-covered lakes located in the McMurdo Dry Valleys (MDV), Antarctica, represent end members in the global network of inland bodies of water. Episodic climatic events in the form of increased summer glacial melt result in inputs of organic sediment and nutrients from glacial streams to these closed basins. Phytoplankton communities residing in the oligotrophic water columns are highly responsive to pulses in nutrient availability; however, there is a lack of understanding on whether specific phytoplankton groups are more competitive during a summer flood event and how shifts in the phytoplankton community may influence heterotrophic bacteria. A bioassay approach in 3-l bottles was used to investigate the influence of inorganic nitrogen and phosphorus availability on planktonic communities from the oligotrophic upper waters of two chemically distinct MDV lakes (Lakes Bonney and Fryxell) which differ in their external inputs and water column N/P stoichiometry. While microbial community responses varied between lakes and were nutrient-dependent, stimulation of phytoplankton biomass and productivity across all treatments was strongly linked with increased abundance of a single phytoplankton phylum (Chlorophyta). Despite stimulation of phytoplankton growth, primary and bacterial productivity was generally uncoupled; however, shifts in bacterial community diversity were observed in bioassays amended with either P or NP. We suggest that climate-associated increases in phytoplankton production and concomitant shifts in diversity will influence MDV bacterial community structure by altering the availability and composition of autochthonous carbon for heterotrophic production.

10aAlgal–bacteria interactions10aclimate change10aMcMurdo Dry Valleys10aNutrient bioassay10aPrimary production1 aTeufel, Amber, G.1 aLi, Wei1 aKiss, Andor, J.1 aMorgan-Kiss, Rachael, M. uhttps://link.springer.com/article/10.1007/s00300-016-2025-802036nas a2200145 4500008004100000245014100041210006900182260001200251490000700263520148900270100002301759700002901782700001701811856006201828 2017 eng d00aMultiple ice-binding proteins of probable prokaryotic origin in an Antarctic lake alga, Chlamydomonas sp. ICE-MDV (Chlorophyceae)0 aMultiple icebinding proteins of probable prokaryotic origin in a c08/20170 v533 a

Ice‐associated algae produce ice‐binding proteins (IBPs) to prevent freezing damage. The IBPs of the three chlorophytes that have been examined so far share little similarity across species, making it likely that they were acquired by horizontal gene transfer (HGT). To clarify the importance and source of IBPs in chlorophytes, we sequenced the IBP genes of another Antarctic chlorophyte, Chlamydomonas sp. ICE‐MDV (Chlamy‐ICE). Genomic DNA and total RNA were sequenced and screened for known ice‐associated genes. Chlamy‐ICE has as many as 50 IBP isoforms, indicating that they have an important role in survival. The IBPs are of the DUF3494 type and have similar exon structures. The DUF3494 sequences are much more closely related to prokaryotic sequences than they are to sequences in other chlorophytes, and the chlorophyte IBP and ribosomal 18S phylogenies are dissimilar. The multiple IBP isoforms found in Chlamy‐ICE and other algae may allow the algae to adapt to a greater variety of ice conditions than prokaryotes, which typically have a single IBP gene. The predicted structure of the DUF3494 domain has an ice‐binding face with an orderly array of hydrophilic side chains. The results indicate that Chlamy‐ICE acquired its IBP genes by HGT in a single event. The acquisitions of IBP genes by this and other species of Antarctic algae by HGT appear to be key evolutionary events that allowed algae to extend their ranges into polar environments.

1 aRaymond, James, A.1 aMorgan-Kiss, Rachael, M.1 aValentin, K. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jpy.1255004197nas a2200253 4500008004100000245012900041210006900170260003900239490001000278520331600288653001503604653002503619653002903644653002903673653002103702653001903723653002403742653002303766653001703789653002303806100002203829700002903851856006303880 2016 eng d00aInfluence of abiotic drivers (light and nutrients) on photobiology and diversity of Antarctic lake phytoplankton communities0 aInfluence of abiotic drivers light and nutrients on photobiology aOxford, OHbMiami Universityc20160 vPh.D.3 a

Arctic, Antarctic, and alpine ecosystems are recognized as sensors and sentinels of global climate change. As a consequence of their high sensitivity to minor climatic perturbations, permanently ice-covered lakes located in the McMurdo Dry Valleys (MCM), Antarctica, represent end members in the global network of inland bodies of water. Episodic climatic events in the form of increased summer glacial melt result in inputs of organic sediment and nutrients from glacial streams to these closed basins. By better understanding how Antarctic lake communities respond to mimicked climate change, we can more accurately predict how they will react to further temperature changes in the future. We began by investigating the influence of inorganic nitrogen and phosphorus availability on planktonic communities residing in the oligotrophic upper waters of two chemically distinct MCM lakes (Lakes Bonney and Fryxell) which differ in their external inputs as well as water column N:P stoichiometry. Although microbial community responses varied between the lakes and were nutrient-dependent, stimulation of phytoplankton biomass and productivity across all treatments was strongly linked with increased abundance of a single phytoplankton phylum (Chlorophyta). Despite stimulation of phytoplankton growth, primary and bacterial productivity were largely uncoupled across all enrichments. We suggest that climate-associated shifts in phytoplankton diversity influence the bacterial community structure by altering the availability and composition of autochthonous carbon for heterotrophic production. To monitor the physiological adaptations that occur over time and depth, we then transplanted two dominant phytoplankton, Chlamydomonas sp. ICE- MDV and Isochrysis sp. MDV back into the Lake Bonney water column. Our results demonstrated that both organisms are specialists for surviving specific depths of the water column and are capable of acclimating to their native environment within a short period of time, and that the chlorophyte Chlamydomonas sp. ICE-MDV most likely makes this adjustment via photoacclimation and accumulating chlorophyll-a per cell. The final study presented here investigated whether or not the dominant chlorophyte, Chlamydomonas sp. ICE-MDV has retained the ability to respond to a diel 12-hour day/night cycle. Although light levels in MCM lakes remain low during the austral summers, daily irradiation varies by as much as tenfold during the course of the day, resulting in a circadian-like light cycle for organisms residing there. With decreased ice coverage on the lakes due to climate change and increased melt, it is likely that these light variations will become amplified over time. This study tested for the presence of a circadian rhythm under various light quality, light quantity, and temperature conditions and demonstrated that although a diel rhythm was maintained in terms of growth and several photochemical parameters, a true circadian rhythm was not identified. Although it is predicted that photosynthetic communities in polar regions will be more responsive to climate warming and episodic events, the complexity of these systems provides numerous challenges to understanding how these organism will adapt in the future.

10aAntarctica10abacterial production10aChlamydomonas sp ICE MDV10aChlorophyll fluorescence10acircadian rhythm10aclimate change10aMcMurdo Dry Valleys10anutrient amendment10aphotobiology10aPrimary production1 aTeufel, Amber, G.1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami146841156403056nas a2200133 4500008004100000245014700041210006900188260003900257490001000296520251200306100001202818700002902830856006302859 2016 eng d00aInfluence of environmental drivers and interactions on the microbial community structures in permanently stratified meromictic Antarctic lakes0 aInfluence of environmental drivers and interactions on the micro aOxford, OHbMiami Universityc20160 vPh.D.3 a

The microbial loop plays important roles in the cycling of energy, carbon and elements in aquatic ecosystems. Viruses, bacteria, Archaea and microbial eukaryotes are key players in global carbon cycle and biogeochemical cycles. Investigating microbial diversity and community structure is crucial first step for understanding the ecological functioning in aquatic environment. Meromictic lakes are bodies of water and exhibit permanent stratification of major physical and chemical environmental factors. Microbial consortia residing in permanently stratified lakes exhibit relatively constant spatial stratification throughout the water column and are adapted to vastly different habitats within the same water. Pristine perennially-ice-covered lakes (Lake Bonney, Lake Fryxell and Lake Vanda) are meromictic lakes located in the McMurdo Dry Valleys (MDV) of Southern Victoria Land, Antarctica. The lakes have isolated water bodies and extremely stable strata that vary physically, chemically, and biologically within and between the water columns. The unique characteristics support microbially dominated food webs in these lakes.

In the research presented here, we gathered new understanding of how environmental drivers influence microbial community structure in these aquatic ecosystems. We explored the lake microbial ecology from three major approaches: 1). Assess trophic activities in the natural environment and identify potential environmental drivers impacting heterotrophic (β Glucosaminidase) and autotrophic (Ribulose 1,5 bisphosphate carboxylase) enzyme activities; 2). Resolve the protist community composition (i.e. autotrophic, heterotrophic and mixotrophic groups) based on high throughput sequencing and bioinformatics. Identify how the community structures correlate with specific environmental and biological factors; 3). Reveal the diversity of potential microbial interactions between the microorganisms in the MDV lakes at individual cell level, and investigate how the interactions vary between organisms with different nutritional strategies.

Studies of polar microbial communities on the cusp of environmental change will be important for predicting how microbial communities in low latitude aquatic systems will respond. This study expands the understanding of how environmental drivers interact with microbial communities in the Antarctica lakes, and provide new information to predict how the community structure will alter as response to climate changes.

1 aLi, Wei1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami146975731600845nas a2200193 4500008004100000022001400041245014300055210006900198260001600267300001400283490000700297100002100304700002800325700002900353700003300382700002200415700002100437856019300458 2016 eng d a0006-356800aMicrobial Community Dynamics in Two Polar Extremes: The Lakes of the McMurdo Dry Valleys and the West Antarctic Peninsula Marine Ecosystem0 aMicrobial Community Dynamics in Two Polar Extremes The Lakes of  cJan-10-2016 a829 - 8470 v661 aBowman, Jeff, S.1 aVick-Majors, Trista, J.1 aMorgan-Kiss, Rachael, M.1 aTakacs-Vesbach, Cristina, D.1 aDucklow, Hugh, W.1 aPriscu, John, C. uhttps://academic.oup.com/bioscience/article-lookup/doi/10.1093/biosci/biw103https://academic.oup.com/bioscience/article/66/10/829/2236137/Microbial-Community-Dynamics-in-Two-Polar-Extremes04082nas a2200157 4500008004100000245010000041210006900141260001200210490000700222520353000229100002903759700002503788700001803813700002103831856007203852 2016 eng d00aPhotoadaptation to the polar night by phytoplankton in a permanently ice-covered Antarctic lake0 aPhotoadaptation to the polar night by phytoplankton in a permane c05/20150 v613 a

Photosynthetic microorganisms are a primary source of new organic carbon production in polar ecosystems. Despite their importance, relatively little is known about how they adapt to the bimodal solar cycles that exist at high latitudes. To understand how phytoplankton adapt to the extreme seasonal change in photoperiod, we transplanted cultures of a well-studied laboratory model for photosynthetic cold adaptation, Chlamydomonas raudensis UWO241, back to the water column of Lake Bonney (McMurdo Dry Valleys, Antarctica) at the depth from which it was originally cultured. The organism was suspended at this depth in dialysis tubing to allow the microalga to respond to the in situ light, temperature and dissolved ions. We then integrated in situ biological and chemical measurements with environmental molecular analyses and compared the responses of transplanted C. raudensis cultures with the natural phytoplankton community over the 6-week transition from Antarctic summer (24-h daylight) to polar night (24-h darkness). As solar radiation declined, natural communities exhibited a cessation of inorganic carbon fixation which was accompanied by a downregulation of expression of genes encoding for essential carbon fixation and photochemistry proteins. Transplanted C. raudensis cultures matched natural community trends in the regulation of photochemistry and carbon fixation gene expression, and shifted photochemical function to a shade adapted state in response to the polar night transition. We present a conceptual model for seasonal shifts in microbial community energy and carbon acquisition which integrates past cultivation-based studies in this model photopsychrophile with a body of recent work on adaptation of natural populations to polar night.

1 aMorgan-Kiss, Rachael, M.1 aLizotte, Michael, P.1 aKong, Weidong1 aPriscu, John, C. uhttps://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.1010700943nas a2200253 4500008004100000022001400041245008700055210006900142260001600211300001400227490000700241100002200248700002100270700002600291700002500317700001200342700002900354700002100383700002100404700002800425700002700453700002200480856018700502 2016 eng d a0006-356800aResponses of Antarctic Marine and Freshwater Ecosystems to Changing Ice Conditions0 aResponses of Antarctic Marine and Freshwater Ecosystems to Chang cJan-10-2016 a864 - 8790 v661 aObryk, Maciek, K.1 aDoran, Peter, T.1 aFriedlaender, Ari, S.1 aGooseff, Michael, N.1 aLi, Wei1 aMorgan-Kiss, Rachael, M.1 aPriscu, John, C.1 aSchofield, Oscar1 aStammerjohn, Sharon, E.1 aSteinberg, Deborah, K.1 aDucklow, Hugh, W. uhttps://academic.oup.com/bioscience/article-lookup/doi/10.1093/biosci/biw109https://academic.oup.com/bioscience/article/66/10/864/2415532/Responses-of-Antarctic-Marine-and-Freshwater04687nas a2200181 4500008004100000022001400041245015900055210006900214260001200283300001600295490000700311520405500318100001204373700001804385700002904403700001804432856005504450 2016 eng d a0099-224000aUltrastructural and Single-Cell-Level Characterization Reveals Metabolic Versatility in a Microbial Eukaryote Community from an Ice-Covered Antarctic Lake0 aUltrastructural and SingleCellLevel Characterization Reveals Met c06/2016 a3659 - 36700 v823 a

The McMurdo Dry Valleys (MCM) of southern Victoria Land, Antarctica, harbor numerous ice-covered bodies of water that provide year-round liquid water oases for isolated food webs dominated by the microbial loop. Single-cell microbial eukaryotes (protists) occupy major trophic positions within this truncated food web, ranging from primary producers (e.g., chlorophytes, haptophytes, and cryptophytes) to tertiary predators (e.g., ciliates, dinoflagellates, and choanoflagellates). To advance the understanding of MCM protist ecology and the roles of MCM protists in nutrient and energy cycling, we investigated potential metabolic strategies and microbial interactions of key MCM protists isolated from a well-described lake (Lake Bonney). Fluorescence-activated cell sorting (FACS) of enrichment cultures, combined with single amplified genome/amplicon sequencing and fluorescence microscopy, revealed that MCM protists possess diverse potential metabolic capabilities and interactions. Two metabolically distinct bacterial clades (Flavobacteria and Methylobacteriaceae) were independently associated with two key MCM lake microalgae (Isochrysis and Chlamydomonas, respectively). We also report on the discovery of two heterotrophic nanoflagellates belonging to the Stramenopila supergroup, one of which lives as a parasite ofChlamydomonas, a dominate primary producer in the shallow, nutrient-poor layers of the lake.

IMPORTANCE Single-cell eukaryotes called protists play critical roles in the cycling of organic matter in aquatic environments. In the ice-covered lakes of Antarctica, protists play key roles in the aquatic food web, providing the majority of organic carbon to the rest of the food web (photosynthetic protists) and acting as the major consumers at the top of the food web (predatory protists). In this study, we utilized a combination of techniques (microscopy, cell sorting, and genomic analysis) to describe the trophic abilities of Antarctic lake protists and their potential interactions with other microbes. Our work reveals that Antarctic lake protists rely on metabolic versatility for their energy and nutrient requirements in this unique and isolated environment.

1 aLi, Wei1 aPodar, Mircea1 aMorgan-Kiss, Rachael, M.1 aKelly, R., M. uhttp://aem.asm.org/lookup/doi/10.1128/AEM.00478-1602282nas a2200181 4500008004100000245010600041210006900147260001200216300001200228490000800240520160500248100001301853700002801866700002901894700002101923700003001944856012601974 2014 eng d00aCiliate diversity, community structure and novel taxa in lakes of the McMurdo Dry Valleys, Antarctica0 aCiliate diversity community structure and novel taxa in lakes of c10/2014 a175-1900 v2273 aWe report an in-depth survey of next-generation DNA sequencing of ciliate diversity and community structure in two permanently ice-covered McMurdo Dry Valley lakes during the austral summer and autumn (November 2007 and March 2008). We tested hypotheses on the relationship between species richness and environmental conditions including environmental extremes, nutrient status, and day length. On the basis of the unique environment that exists in these high-latitude lakes, we expected that novel taxa would be present. Alpha diversity analyses showed that extreme conditions-that is, high salinity, low oxygen, and extreme changes in day length-did not impact ciliate richness; however, ciliate richness was 30% higher in samples with higher dissolved organic matter. Beta diversity analyses revealed that ciliate communities clustered by dissolved oxygen, depth, and salinity, but not by season (i.e., day length). The permutational analysis of variance test indicated that depth, dissolved oxygen, and salinity had significant influences on the ciliate community for the abundance matrices of resampled data, while lake and season were not significant. This result suggests that the vertical trends in dissolved oxygen concentration and salinity may play a critical role in structuring ciliate communities. A PCR-based strategy capitalizing on divergent eukaryotic V9 hypervariable region ribosomal RNA gene targets unveiled two new genera in these lakes. A novel taxon belonging to an unknown class most closely related to Cryptocaryon irritans was also inferred from separate gene phylogenies.1 aYuan, Xu1 aVick-Majors, Trista, J.1 aMorgan-Kiss, Rachael, M.1 aPriscu, John, C.1 aAmaral-Zettler, Linda, A. uhttps://mcm.lternet.edu/content/ciliate-diversity-community-structure-and-novel-taxa-lakes-mcmurdo-dry-valleys-antarctica03186nas a2200181 4500008004100000245010400041210006900145260003900214490001000253520255800263653002002821653001602841653002202857653001202879100002102891700002902912856006302941 2014 eng d00aEnvironmental impacts on RubisCO from green algal laboratory isolates to Antarctic lake communities0 aEnvironmental impacts on RubisCO from green algal laboratory iso aOxford, OHbMiami Universityc20140 vPh.D.3 a

Ribulose-1,5-bisphosphate carboxylase oxygenase (RubisCO) is found in a variety of autotrophic microorganisms ranging from green algae, cyanobacteria, and chemoautotrophic bacteria. As this enzyme has the potential to catalyze carboxylation (carbon fixation) or oxygenation (photorespiration) reactions, it is regulated in response to environmental variables at the levels of transcription, translation, and post-translation by the enzyme, RubisCO activase. A combination of laboratory experiments on green algal isolates and field experiments were utilized to gain insight on carbon fixation in permanently ice-covered Antarctic lakes. RubisCO was investigated as a potential target for cold adaptation of carbon fixation in the psychrophilic green alga, Chlamydomonas raudensis UWO241 (UWO241), isolated from Lake Bonney, Antarctica. RubisCO activity, stability, and whole cell carbon fixation were measured for the psychrophile and compared to a closely related mesophilic alga, C. raudensis SAG49.72 (SAG49.72). The effect of environmental factors including light and temperature on UWO241 and SAG49.72 RubisCO activation state, an indirect measurement of RubisCO activase activity, and abundance was investigated using a modified RubisCO carboxylase assay and immunoblotting, respectively. Lastly, maximum potential RubisCO carboxylase activity was determined using a modified activity assay in multiple ice covered Antarctic lakes including Lake Bonney. This data was complemented with lake depth profiles of enzyme abundance determined by quantitative real-time PCR and RubisCO-harboring organism diversity. While purified RubisCO of the psychrophilic green alga did not function optimally at low temperature, whole cell carbon fixation was greater under such conditions, suggesting that the overall process of carbon fixation is modified to function in UWO241. Increased RubisCO abundance at low temperature may contribute to this phenomenon. Low light levels may be important in regulation of RubisCO via RubisCO activase and should be further investigated. Based on community level RubsiCO activity and enzyme abundance, light and RubisCO harboring organisms including eukaryotic algae and cyanobacteria were positively correlated, but this was variable between lakes. Dark carbon fixation was potentially important in lakes west lobe Bonney and Fryxell and this community was negatively correlated with light. Results of targeted physiology and community level experiments led to development of a carbon fixation model for Lake Bonney.

10acarbon fixation10agreen algae10aice-covered lakes10aRubisCO1 aDolhi, Jenna, M.1 aMorgan-Kiss, Rachael, M. uhttp://rave.ohiolink.edu/etdc/view?acc_num=miami140705678300561nas a2200157 4500008004100000245012400041210006900165260001200234300001400246490000700260100001800267700002000285700002100305700002900326856004800355 2012 eng d00aDiversity and Expression of RubisCO Genes in a Perennially Ice-Covered Antarctic Lake during the Polar Night Transition0 aDiversity and Expression of RubisCO Genes in a Perennially IceCo c04/2012 a4358-43660 v781 aKong, Weidong1 aReam, David, C.1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttp://aem.asm.org/content/78/12/4358.short00583nas a2200169 4500008004100000245008400041210006900125260001200194300001400206490000700220100001800227700002100245700002000266700002100286700002900307856007700336 2012 eng d00aEvidence of form II RubisCO ( cbbM) in a perennially ice-covered Antarctic lake0 aEvidence of form II RubisCO cbbM in a perennially icecovered Ant c11/2012 a491 - 5000 v821 aKong, Weidong1 aDolhi, Jenna, M.1 aChiuchiolo, Amy1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttp://onlinelibrary.wiley.com/doi/10.1111/j.1574-6941.2012.01431.x/full00623nas a2200181 4500008004100000245010000041210006900141260001100210300001600221490000600237100002100243700002100264700001800285700002000303700002100323700002900344856006800373 2011 eng d00aProtist diversity in a permanently ice-covered Antarctic Lake during the polar night transition0 aProtist diversity in a permanently icecovered Antarctic Lake dur c9/2011 a1559 - 15640 v51 aBielewicz, Scott1 aBell, Elanor, R.1 aKong, Weidong1 aFriedberg, Iddo1 aPriscu, John, C.1 aMorgan-Kiss, Rachael, M. uhttp://www.nature.com/ismej/journal/v5/n9/abs/ismej201123a.html00684nas a2200169 4500008004100000245012300041210006900164260001100233300001400244490000700258100002800265700002400293700002900317700002100346700001800367856012900385 2010 eng d00aOrigin and tentative identification of tri to pentaunsaturated ketones in sediments from Lake Fryxell, East Antarctica0 aOrigin and tentative identification of tri to pentaunsaturated k c4/2010 a386 - 3970 v411 aJaraula, Caroline, M.B.1 aBrassell, Simon, C.1 aMorgan-Kiss, Rachael, M.1 aDoran, Peter, T.1 aKenig, Fabien uhttps://mcm.lternet.edu/content/origin-and-tentative-identification-tri-pentaunsaturated-ketones-sediments-lake-fryxell-east02534nas a2200193 4500008004100000245009700041210006900138260001200207300001200219490000700231520185500238653001102093100002902104700002102133700001402154700002502168700002402193856012302217 2006 eng d00aAdaptation and acclimation of photosynthetic microorganisms to permanently cold environments0 aAdaptation and acclimation of photosynthetic microorganisms to p c03/2006 a222-2520 v703 a

Persistently cold environments constitute one of our world's largest ecosystems, and microorganisms dominate the biomass and metabolic activity in these extreme environments. The stress of low temperatures on life is exacerbated in organisms that rely on photoautrophic production of organic carbon and energy sources. Phototrophic organisms must coordinate temperature-independent reactions of light absorption and photochemistry with temperature-dependent processes of electron transport and utilization of energy sources through growth and metabolism. Despite this conundrum, phototrophic microorganisms thrive in all cold ecosystems described and (together with chemoautrophs) provide the base of autotrophic production in low-temperature food webs. Psychrophilic (organisms with a requirement for low growth temperatures) and psychrotolerant (organisms tolerant of low growth temperatures) photoautotrophs rely on low-temperature acclimative and adaptive strategies that have been described for other low-temperature-adapted heterotrophic organisms, such as cold-active proteins and maintenance of membrane fluidity. In addition, photoautrophic organisms possess other strategies to balance the absorption of light and the transduction of light energy to stored chemical energy products (NADPH and ATP) with downstream consumption of photosynthetically derived energy products at low temperatures. Lastly, differential adaptive and acclimative mechanisms exist in phototrophic microorganisms residing in low-temperature environments that are exposed to constant low-light environments versus high-light- and high-UV-exposed phototrophic assemblages.

10aBiggie1 aMorgan-Kiss, Rachael, M.1 aPriscu, John, C.1 aPocock, T1 aGudynaite-Savitch, L1 aHuner, Norman, P.A. uhttps://mcm.lternet.edu/content/adaptation-and-acclimation-photosynthetic-microorganisms-permanently-cold-environments00640nas a2200157 4500008004100000245011400041210006900155300001200224490000700236100002400243700002600267700002100293700002300314700002400337856012100361 1998 eng d00aStructure and composition of the photochemical apparatus of the Antarctic green alga Chlamydomonas subcaudata0 aStructure and composition of the photochemical apparatus of the  a303-3140 v561 aMorgan, Rachael, M.1 aIvanov, Alexander, G.1 aPriscu, John, C.1 aMaxwell, Denis, P.1 aHuner, Norman, P.A. uhttps://mcm.lternet.edu/content/structure-and-composition-photochemical-apparatus-antarctic-green-alga-chlamydomonas