02367nas a2200205 4500008004100000245011400041210006900155260001200224300001400236490000800250520166200258100002501920700002701945700002801972700002602000700002002026700002002046700002102066856007402087 2019 eng d00aDifferential incorporation of bacteria, organic matter, and inorganic ions into lake ice during ice formation0 aDifferential incorporation of bacteria organic matter and inorga c02/2019 a585 - 6000 v1243 a

The segregation of bacteria, inorganic solutes, and total organic carbon between liquid water and ice during winter ice formation on lakes can significantly influence the concentration and survival of microorganisms in icy systems, and their roles in biogeochemical processes. Our study quantifies the distributions of bacteria and solutes between liquid and solid water phases during progressive freezing. We simulated lake ice formation in mesocosm experiments using water from perennially (Antarctica) and seasonally (Alaska and Montana, USA) ice covered lakes. We then computed concentration factors and effective segregation coefficients, which are parameters describing the incorporation of bacteria and solutes into ice. Experimental results revealed that, contrary to major ions, bacteria were readily incorporated into ice and did not concentrate in the liquid phase. The organic matter incorporated into the ice was labile, amino acid-like material, differing from the humic-like compounds that remained in the liquid phase. Results from a control mesocosm experiment (dead bacterial cells) indicated that viability of bacterial cells did not influence the incorporation of free bacterial cells into ice, but did have a role in the formation and incorporation of bacterial aggregates. Together, these findings demonstrate that bacteria, unlike other solutes, were preferentially incorporated into lake-ice during our freezing experiments, a process controlled mainly by the initial solute concentration of the liquid water source, regardless of cell viability.

1 aSantibáñez, Pamela1 aMichaud, Alexander, B.1 aVick-Majors, Trista, J.1 aD’Andrilli, Juliana1 aChiuchiolo, Amy1 aHand, Kevin, P.1 aPriscu, John, C. uhttps://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JG00482502147nas a2200193 4500008004100000022001400041245007800055210006900133260001200202490000700214520142200221653002201643653001801665653002001683653002501703100002801728700002101756856017601777 2019 eng d a0954-102000aInorganic carbon fixation in ice-covered lakes of the McMurdo Dry Valleys0 aInorganic carbon fixation in icecovered lakes of the McMurdo Dry c04/20190 v723 a

Inorganic carbon fixation, usually mediated by photosynthetic microorganisms, is considered to form the base of the food chain in aquatic ecosystems. In high-latitude lakes, lack of sunlight owing to seasonal solar radiation limits the activity of photosynthetic plankton during the polar winter, causing respiration-driven demand for carbon to exceed supply. Here, we show that inorganic carbon fixation in the dark, driven by organisms that gain energy from chemical reactions rather than sunlight (chemolithoautotrophs), provides a significant influx of fixed carbon to two permanently ice-covered lakes (Fryxell and East Bonney). Fryxell, which has higher biomass per unit volume of water, had higher rates of inorganic dark carbon fixation by chemolithoautotrophs than East Bonney (trophogenic zone average 1.0 µg C l−1 d−1 vs 0.08 µg C l−1 d−1, respectively). This contribution from dark carbon fixation was partly due to the activity of ammonia oxidizers, which are present in both lakes. Despite the potential importance of new carbon input by chemolithoautotrophic activity, both lakes remain net heterotrophic, with respiratory demand for carbon exceeding supply. Dark carbon fixation increased the ratio of new carbon supply to respiratory demand from 0.16 to 0.47 in Fryxell, and from 0.14 to 0.22 in East Bonney.

10aammonia oxidation10acarbon budget10achemoautotrophy10achemolithoautotrophy1 aVick-Majors, Trista, J.1 aPriscu, John, C. uhttps://www.cambridge.org/core/journals/antarctic-science/article/inorganic-carbon-fixation-in-icecovered-lakes-of-the-mcmurdo-dry-valleys/4B5CA9E91C85B307EFDA69F8D7B5BFD902857nas a2200133 4500008004100000245008900041210006900130260002900199300000800228490001000236520233500246100002802581856011402609 2016 eng d00aBiogeochemical processes in Antarctic aquatic environments: Linkages and limitations0 aBiogeochemical processes in Antarctic aquatic environments Linka bMontana State University a2280 vPh.D.3 a

The research presented in this dissertation focused on microbially-mediated biogeochemical processes and microbial ecology in Antarctic lakes and seawater. The major objective of my research was to examine the impact of environmentally imposed energetic constraints on nutrient cycling in mirobially-dominated systems. I used three ice-covered aquatic environments as natural laboratories for my investigations. The permanently ice-covered lakes of the McMurdo Dry Valleys (MCM) are located in Victoria Land, East Antarctica. The MCM have been studied intensively as part of the McMurdo Long Term Ecological Research Project since 1993. My work built on the extensive MCM dataset via high-throughput DNA sequencing to examine microbial communities from all three domains of life during the transition to winter, and by quantifying rates of dark inorganic carbon-fixation. This worked showed the importance of flexible metabolisms in the microbial ecosystems of the MCM lakes. The ocean beneath the McMurdo Ice Shelf (MIS) is the gateway between the Ross Sea and the dark ocean of the Ross Ice Shelf cavity. The area supports a biological carbon pump that is important in ocean biogeochemistry. Ice shelves around Antarctica are under threat of collapse, but little is known about the ecosystems beneath them. My work used a combination of biogeochemical measurements and assessment of microbial community structure to characterize the ecosystem beneath the MIS and its connections to the open ocean. The data showed the importance of nutrients advected from open water to the MIS cavity and projected an organic carbon deficit farther from the ice shelf edge. Subglacial Lake Whillans lies 800 m beneath the surface of the West Antarctic Ice Sheet near the end of a hydrological continuum that terminates in the ocean beneath the Ross Ice Shelf. Primarily through the use of biogeochemical rate measurements and determinations of organic matter quantity and quality, this work established the presence of an active microbial ecosystem in the subglacial lake, and estimated the annual subglacial flux of carbon and nutrients to the ocean under the ice shelf. Together, these projects show the importance of microbial activity in regional biogeochemical processes and of metabolic flexibility under energy-limited conditions.

1 aVick-Majors, Trista, J. uhttps://search.proquest.com/openview/9118336399cac113f488d77fb07bce26/1?pq-origsite=gscholar&cbl=18750&diss=y01022nas a2200289 4500008004100000245010700041210006900148260001200217300001400229490000700243100002800250700002200278700002500300700001900325700002000344700002700364700002500391700002600416700002300442700001700465700001900482700002000501700002100521700001800542700002100560856015100581 2016 eng d00aBiogeochemistry and microbial diversity in the marine cavity beneath the McMurdo Ice Shelf, Antarctica0 aBiogeochemistry and microbial diversity in the marine cavity ben c11/2015 a572 - 5860 v611 aVick-Majors, Trista, J.1 aAchberger, Amanda1 aSantibáñez, Pamela1 aDore, John, E.1 aHodson, Timothy1 aMichaud, Alexander, B.1 aChristner, Brent, C.1 aAi, Jill., Mikucki Ji1 aSkidmore, Mark, L.1 aPowell, Ross1 aAdkins, Peyton1 aBarbante, Carlo1 aMitchell, Andrew1 aScherer, Reed1 aPriscu, John, C. uhttp://doi.wiley.com/10.1002/lno.v61.2http://doi.wiley.com/10.1002/lno.10234http://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Flno.1023400845nas 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-Extremes00604nas a2200169 4500008004100000245007900041210006900120260001600189490000600205100002200211700002500233700002700258700002100285700002300306700002800329856007700357 2016 eng d00aMicrobial Community Structure of Subglacial Lake Whillans, West Antarctica0 aMicrobial Community Structure of Subglacial Lake Whillans West A cOct-09-20170 v71 aAchberger, Amanda1 aChristner, Brent, C.1 aMichaud, Alexander, B.1 aPriscu, John, C.1 aSkidmore, Mark, L.1 aVick-Majors, Trista, J. uhttp://journal.frontiersin.org/Article/10.3389/fmicb.2016.01457/abstract00836nas a2200229 4500008004100000245007200041210006900113260001600182490000600198100002800204700002100232700002200253700002500275700001900300700002700319700002200346700002400368700002300392700002100415710002900436856014100465 2016 eng d00aPhysiological Ecology of Microorganisms in Subglacial Lake Whillans0 aPhysiological Ecology of Microorganisms in Subglacial Lake Whill cMar-10-20180 v71 aVick-Majors, Trista, J.1 aMitchell, Andrew1 aAchberger, Amanda1 aChristner, Brent, C.1 aDore, John, E.1 aMichaud, Alexander, B.1 aMikucki, Jill, A.1 aPurcell, Alicia, M.1 aSkidmore, Mark, L.1 aPriscu, John, C.1 aThe WISSARD Science Team uhttp://journal.frontiersin.org/article/10.3389/fmicb.2016.01705/fullhttp://journal.frontiersin.org/article/10.3389/fmicb.2016.01705/full02282nas 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-antarctica00531nas a2200121 4500008004100000245013000041210006900171260001200240100002800252700002100280700003000301856007800331 2014 eng d00aModular community structure suggests metabolic plasticity during the transition to polar night in ice-covered Antarctic lakes0 aModular community structure suggests metabolic plasticity during c10/20131 aVick-Majors, Trista, J.1 aPriscu, John, C.1 aAmaral-Zettler, Linda, A. uhttp://www.nature.com/ismej/journal/vaop/ncurrent/full/ismej2013190a.html03100nas a2200157 4500008004100000022001400041245011100055210006900166260001200235300001200247490000700259520257200266100002802838700002102866856005502887 2012 eng d a0948-305500aBacterioplankton productivity in lakes of the Taylor Valley, Antarctica, during the polar night transition0 aBacterioplankton productivity in lakes of the Taylor Valley Anta c12/2013 a77 - 900 v683 a

Research on the lakes of the McMurdo Dry Valleys, Antarctica, is typically conducted during the period of 24 h sunlight (October to January) when logistical support is readily available. As part of the International Polar Year initiative, we obtained logistical support to study microbial dynamics in the permanently ice-covered lakes of the Taylor Valley during the transition from 24 h of sunlight to the complete darkness of the polar night (mid-April). Our study focused on the perennially ice-covered lakes Fryxell (FRX), East Lobe Bonney (ELB), and West Lobe Bonney (WLB), all of which are chemically stratified and have food webs dominated by microorganisms. Depth-integrated bacterioplankton productivity (BP; leucine incorporation [Leu] and thymidine incorporation [TdR]) in the lakes ranged from 1.2 to 3.4 mg C m−2 d−1. Overall, summer was characterized by relatively high rates of BP and photoautotrophic primary productivity. Rapid decreases in photosynthetically active radiation marked a subsequent transition period, which was characterized by variable cell counts and decreasing Leu:TdR ratios (ratios >1 signify a physiological shift from growth to maintenance mode). Finally, cell counts decreased and Leu:TdR increased by as much as 280% during the fall, revealing a distinct change in the physiological state of the bacterioplankton as light-mediated primary productivity ceased. Our data reveal that the shift in physiological state may result from a switch from contemporary phytoplankton-excreted carbon to other sources of dissolved organic carbon, which can support the bacterioplankton populations through the winter.

1 aVick-Majors, Trista, J.1 aPriscu, John, C. uhttp://www.int-res.com/abstracts/ame/v68/n1/p77-9000684nas a2200193 4500008004100000245011200041210006900153260001200222300001400234490000700248100001800255700002200273700002100295700002100316700002800337700002000365700002800385856007700413 2012 eng d00aMicrobial dynamics and flagellate grazing during transition to winter in Lakes Hoare and Bonney, Antarctica0 aMicrobial dynamics and flagellate grazing during transition to w c11/2012 a449 - 4580 v821 aThurman, Jill1 aParry, Jacqueline1 aHill, Philip, J.1 aPriscu, John, C.1 aVick-Majors, Trista, J.1 aChiuchiolo, Amy1 aLaybourn-Parry, Johanna uhttp://onlinelibrary.wiley.com/doi/10.1111/j.1574-6941.2012.01423.x/full02548nas a2200145 4500008004100000245011900041210006900160260004800229300000700277490000900284520200300293100002802296700002102324856005702345 2010 eng d00aBacterioplakton dynamics in stratified lakes of the Taylor Valley, Antarctica during the transition to polar night0 aBacterioplakton dynamics in stratified lakes of the Taylor Valle aBozeman, MTbMontana State Universityc2010 a830 vM.S.3 a

Limnological research on the lakes of the McMurdo Dry Valleys (MCM), Antarctica, is typically carried out during the austral spring-summer (October January) when logistical support is readily available; the current study marks the first sampling effort during the summer-fall transition (January-April). Sampling during the darkness of winter is logistically difficult and expensive, and my study is an important step towards understanding the year-round ecology of the dry valley lakes. Bacterial productivity, measured as protein synthesis and DNA replication, and bacterial cell numbers were measured 10-12 times between October 2007 and April 2008 in Lakes Fryxell (FRX) and the east and west lobes of Lake Bonney (ELB and WLB). Lake Fryxell was the most productive (bacterial) lake on average by an order of magnitude (average = 1.24 mg C m -²d -¹; range = 0.00 to 3.29 mg C m -²d -¹), and also contained the greatest bacterial biomass (~10 ⁶ cells ml -¹) by 1 to 3 orders of magnitude. If bacterial production were directly linked to organic carbon supplied by photosynthetic primary production, a decrease in bacterial production would be expected during the sunset; however, no statistically significant change in bacterial production (a=0.05) was observed during the summer-fall transition. A distinct decoupling of bacterial protein production and DNA replication was detected in FRX and ELB of the lakes as the season progressed, and was present in WLB throughout the season, indicating either a shift towards a lower growth-rate in response to decreasing light or nutrient supply, or a mechanism for dealing with the perennially low temperatures, low light, and nutrient poor conditions in the lakes. Overall, it appears that bacterial communities remain active during the darkness of winter, when the lakes enter a period of "net heterotrophy", which cannot be sustained unless the carbon balance of the TV lakes is reset by climatic events.

1 aVick-Majors, Trista, J.1 aPriscu, John, C. uhttps://scholarworks.montana.edu/xmlui/handle/1/2477