02426nas a2200241 4500008004100000022001400041245010000055210006900155260001200224490000800236520166500244653001501909653001701924653002901941653002401970653002201994653001902016100002202035700002202057700001502079700002102094856006902115 2025 eng d a2169-895300aMorphology and distribution of bubble-supported microbial mats from ice-covered Antarctic lakes0 aMorphology and distribution of bubblesupported microbial mats fr c03/20250 v1303 a

Gas bubbles directly influence the macromorphology of benthic microbial mats resulting in preservable biosedimentary structures. This study characterizes the morphology and distribution of microbial mats growing in gas-supersaturated, perennially ice-covered lakes Fryxell, Joyce, and Hoare of the McMurdo Dry Valleys of Antarctica. Photosynthetic benthic mats within the gas-supersaturated zone trap oxygen-rich bubbles and become buoyant, tearing off the bottom as “liftoff mats.” These liftoff mats form a succession of morphologies starting with bubble-induced deformation of flat mats into tent, ridge, and finger liftoff mat. With progressive deformation, mats tear, forming sheet liftoff, while multiple cycles of deformation and tearing transform sheet into strip liftoff. Some mats detach from the substrate and float to the underside of the ice. The depth range of the liftoff zone has varied over time at each lake. Downslope expansion of bubble formation brings previously bubble-free, deep-water pinnacle mats into the liftoff zone. When the liftoff zone shallows, liftoff mats at the deeper end deflate and can become scaffolding for additional mat growth. The superposition and relative orientation of liftoff and pinnacle mats can be used to track the maximum depth of the liftoff zone and changes in gas saturation state in these lakes through time. Our results demonstrate that gas bubbles, even when they are transitory, can exert a significant impact on the morphology of microbial mats at larger scales. This provides a way to identify similar structures and gas supersaturated environments in the biosedimentary record.

10aAntarctica10abiosediments10abubble-driven morphology10agas-supersaturation10aice-covered lakes10amicrobial mats1 aJuarez-Rivera, M.1 aMackey, Tyler, J.1 aHawes, Ian1 aSumner, Dawn, Y. uhttps://agupubs.onlinelibrary.wiley.com/doi/10.1029/2024JG00851602224nas a2200229 4500008004100000245016400041210006900205260001200274300000800286490000700294520144700301100002401748700002301772700002201795700001501817700002101832700002201853700002201875700003201897700002101929856004401950 2021 eng d00aMetabolic capacity of the Antarctic cyanobacterium Phormidium pseudopriestleyi that sustains oxygenic photosynthesis in the presence of hydrogen sulfide0 aMetabolic capacity of the Antarctic cyanobacterium IPhormidium p c03/2021 a4260 v123 a

Sulfide inhibits oxygenic photosynthesis by blocking electron transfer between H2O and the oxygen-evolving complex in the D1 protein of Photosystem II. The ability of cyanobacteria to counter this effect has implications for understanding the productivity of benthic microbial mats in sulfidic environments throughout Earth history. In Lake Fryxell, Antarctica, the benthic, filamentous cyanobacterium Phormidium pseudopriestleyi creates a 1–2 mm thick layer of 50 µmol L−1 O2 in otherwise sulfidic water, demonstrating that it sustains oxygenic photosynthesis in the presence of sulfide. A metagenome-assembled genome of P. pseudopriestleyi indicates a genetic capacity for oxygenic photosynthesis, including multiple copies of psbA (encoding the D1 protein of Photosystem II), and anoxygenic photosynthesis with a copy of sqr (encoding the sulfide quinone reductase protein that oxidizes sulfide). The genomic content of P. pseudopriestleyi is consistent with sulfide tolerance mechanisms including increasing psbA expression or directly oxidizing sulfide with sulfide quinone reductase. However, the ability of the organism to reduce Photosystem I via sulfide quinone reductase while Photosystem II is sulfide-inhibited, thereby performing anoxygenic photosynthesis in the presence of sulfide, has yet to be demonstrated. 

1 aLumian, Jessica, E.1 aJungblut, Anne, D.1 aDillon, Megan, L.1 aHawes, Ian1 aDoran, Peter, T.1 aMackey, Tyler, J.1 aDick, Gregory, J.1 aGrettenberger, Christen, L.1 aSumner, Dawn, Y. uhttps://www.mdpi.com/2073-4425/12/3/42602314nas a2200265 4500008004100000245012500041210006900166260001200235490000700247520147000254653001501724653001101739653001701750653001801767653001101785653004001796100002201836700001501858700002301873700002201896700002401918700002101942700002101963856006401984 2020 eng d00aEnergetic and environmental constraints on the community structure of benthic microbial mats in Lake Fryxell, Antarctica0 aEnergetic and environmental constraints on the community structu c02/20200 v963 a

Ecological communities are regulated by the flow of energy through environments. Energy flow is typically limited by access to photosynthetically active radiation (PAR) and oxygen concentration (O2). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O2). We analyzed the metagenomes of layers from these microbial mats to test the extent to which access to oxygen and light controls community structure. We found variation in the diversity and relative abundances of Archaea, Bacteria and Eukaryotes across three (O2) and PAR conditions: high (O2) and maximum PAR, variable (O2) with lower maximum PAR, and low (O2) and maximum PAR. We found distinct communities structured by the optimization of energy use on a millimeter-scale across these conditions. In mat layers where (O2) was saturated, PAR structured the community. In contrast, (O2) positively correlated with diversity and affected the distribution of dominant populations across the three habitats, suggesting that meter-scale diversity is structured by energy availability. Microbial communities changed across covarying gradients of PAR and (O2). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.

10aAntarctica10aenergy10aLake Fryxell10amicrobial mat10aOxygen10aPhotosynthetically Active Radiation1 aDillon, Megan, L.1 aHawes, Ian1 aJungblut, Anne, D.1 aMackey, Tyler, J.1 aEisen, Jonathan, A.1 aDoran, Peter, T.1 aSumner, Dawn, Y. uhttps://academic.oup.com/femsec/article/96/2/fiz207/569719602205nas a2200205 4500008004100000245012400041210006900165260001200234300001300246490000700259520150700266100002201773700001501795700002301810700002201833700002401855700002101879700002101900856007801921 2020 eng d00aEnvironmental control on the distribution of metabolic strategies of benthic microbial mats in Lake Fryxell, Antarctica0 aEnvironmental control on the distribution of metabolic strategie c04/2020 ae02310530 v153 a

Ecological theories posit that heterogeneity in environmental conditions greatly affects community structure and function. However, the degree to which ecological theory developed using plant- and animal-dominated systems applies to microbiomes is unclear. Investigating the metabolic strategies found in microbiomes are particularly informative for testing the universality of ecological theories because microorganisms have far wider metabolic capacity than plants and animals. We used metagenomic analyses to explore the relationships between the energy and physicochemical gradients in Lake Fryxell and the metabolic capacity of its benthic microbiome. Statistical analysis of the relative abundance of metabolic marker genes and gene family diversity shows that oxygenic photosynthesis, carbon fixation, and flavin-based electron bifurcation differentiate mats growing in different environmental conditions. The pattern of gene family diversity points to the likely importance of temporal environmental heterogeneity in addition to resource gradients. Overall, we found that the environmental heterogeneity of photosynthetically active radiation (PAR) and oxygen concentration ([O2]) in Lake Fryxell provide the framework by which metabolic diversity and composition of the community is structured, in accordance with its phylogenetic structure. The organization of the resulting microbial ecosystems are consistent with the maximum power principle and the species sorting model.

1 aDillon, Megan, L.1 aHawes, Ian1 aJungblut, Anne, D.1 aMackey, Tyler, J.1 aEisen, Jonathan, A.1 aDoran, Peter, T.1 aSumner, Dawn, Y. uhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.023105302475nas a2200229 4500008004100000020002200041245008100063210006900144260004400213300001300257520171900270653001201989653002202001653002502023653003102048653001702079100001502096700002102111700002302132700002402155856006602179 2019 eng d a978-3-030-16775-200aComplex Structure but Simple Function in Microbial Mats from Antarctic Lakes0 aComplex Structure but Simple Function in Microbial Mats from Ant aChambSpringer International Publishing a91 - 1203 a

Microbial mats growing under the permanent ice cover of Antarctic lakes occupy an exceptionally low-disturbance regime. Constant temperature, the absence of bioturbation or physical disturbance from wind action or ice formation allow mats to accumulate, as annual growth layers, over many decades or even centuries. In so doing they often assume decimetre scale, three-dimensional morphologies such as elaborate pinnacle structures and conical mounds. Here we combine existing and new information to describe microbial structures in three Antarctic lakes—simple prostrate mats in Lake Hoare, emergent cones in Lake Untersee and elaborate pinnacles in Lake Vanda. We attempt to determine whether structures emerge simply from uncoordinated organism-environment interactions or whether they represent an example of “emergent complexity”, within which some degree of self-organisation occurs to confer a holistic functional advantage to component organisms. While some holistic advantages were evident from the structures—the increase in surface area allows greater biomass and overall productivity and nutrient exchange with overlying water—the structures could also be understood in terms of potential interactions between individuals, their orientation and their environment. The data lack strong evidence of coordinated behaviour directed towards holistic advantages to the structure, though hints of coordinated behaviour are present as non-random distributions of structural elements. The great size of microbial structures in Antarctic lakes, and their relatively simple community composition, makes them excellent models for more focused research on microbial cooperation.

10abiofilm10amicrobial ecology10amicrobial structures10aself-organising structures10astromatolite1 aHawes, Ian1 aSumner, Dawn, Y.1 aJungblut, Anne, D.1 aHurst, Christon, J. uhttps://link.springer.com/chapter/10.1007/978-3-030-16775-2_402611nas a2200253 4500008004100000245011600041210006900157260001200226520177500238653001202013653002502025653003202050653001402082653002402096100002102120700002202141700002802163700002102191700002302212700002102235700001502256700002302271856006302294 2019 eng d00aEnvironmental controls on bacteriohopanepolyol profiles of benthic microbial mats from Lake Fryxell, Antarctica0 aEnvironmental controls on bacteriohopanepolyol profiles of benth c07/20193 a

Bacteriohopanepolyols (BHPs) are pentacyclic triterpenoid lipids that contribute to the structural integrity and physiology of some bacteria. Because some BHPs originate from specific classes of bacteria, BHPs have potential as taxonomically and environmentally diagnostic biomarkers. For example, a stereoisomer of bacteriohopanetetrol (informally BHT II) has been associated with anaerobic ammonium oxidation (anammox) bacteria and suboxic to anoxic marine environments where anammox is active. As a result, the detection of BHT II in the sedimentary record and fluctuations in the relative abundance of BHT II may inform reconstructions of nitrogen cycling and ocean redox changes through the geological record. However, there are uncertainties concerning the sources of BHT II and whether or not BHT II is produced in abundance in non‐marine environments, both of which are pertinent to interpretations of BHT II signatures in sediments. To address these questions, we investigate the BHP composition of benthic microbial mats from Lake Fryxell, Antarctica. Lake Fryxell is a perennially ice‐covered lake with a sharp oxycline in a density‐stabilized water column. We describe the diversity and abundance of BHPs in benthic microbial mats across a transect from oxic to anoxic conditions. Generally, BHP abundances and diversity vary with the morphologies of microbial mats, which were previously shown to reflect local environmental conditions, such as irradiance and oxygen and sulfide concentrations. BHT II was identified in mats that exist within oxic to anoxic portions of the lake. However, anammox bacteria have yet to be identified in Lake Fryxell. We examine our results in the context of BHPs as biomarkers in modern and ancient environments.

10aanammox10abacteriohopanepolyol10abacteriohopanetetrol isomer10abiomarker10aMcMurdo Dry Valleys1 aMatys, Emily, D.1 aMackey, Tyler, J.1 aGrettenberger, Christen1 aMueller, Elliott1 aJungblut, Anne, D.1 aSumner, Dawn, Y.1 aHawes, Ian1 aSummons, Roger, E. uhttps://onlinelibrary.wiley.com/doi/full/10.1111/gbi.1235302449nas a2200169 4500008004100000245008400041210006900125260001200194490000700206520189300213100003002106700002102136700002202157700001502179700002302194856006202217 2019 eng d00aIn a PICL: The sedimentary deposits and facies of perennially ice-covered lakes0 aIn a PICL The sedimentary deposits and facies of perennially ice c04/20190 v663 a

Perennially ice‐covered lakes can have significantly different facies than open‐water lakes because sediment is transported onto the ice, where it accumulates, and sand grains preferentially melt through to be deposited on the lake floor. To characterize the facies in these lakes, sedimentary deposits from five Antarctic perennially ice‐covered lakes were described using lake‐bottom observations, underwater video and images, and sediment cores. One lake was dominated by laminated microbial mats and mud (derived from an abutting glacier), with disseminated sand and rare gravel. The other four lakes were dominated by laminated microbial mats and moderately well to moderately sorted medium to very coarse sand with sparse granules and pebbles; they contained minor interstitial or laminated mud (derived from streams and abutting glaciers). The sand was disseminated or localized in mounds and 1 m to more than 10 m long elongate ridges. Mounds were centimetres to metres in diameter; conical, elongate or round in shape; and isolated or deposited near or on top of one another. Sand layers in the mounds had normal, inverse, or no grading. Nine mixed mud and sand facies were defined for perennially ice‐covered lakes based on the relative proportion of mud to sand and the style of sand deposition. While perennially ice‐covered lake facies overlap with other ice‐influenced lakes and glaciomarine facies, they are characterized by a paucity of grains coarser than granules, a narrow range in sand grain sizes, and inverse grading in the sand mounds. These facies can be used to infer changes in ice cover through time and to identify perennially ice‐covered lakes in the rock record. Ancient perennially ice‐covered lakes are expected on Earth and Mars, and their characterization will provide new insights into past climatic conditions and habitability.

1 aRivera-Hernandez, Frances1 aSumner, Dawn, Y.1 aMackey, Tyler, J.1 aHawes, Ian1 aAndersen, Dale, T. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/sed.1252200761nas a2200241 4500008004100000022001400041245009900055210006900154260001200223300001400235490000700249100002300256700001500279700002200294700001800316700002100334700002100355700002400376700001900400700002700419700001800446856005500464 2016 eng d a0099-224000aMicrobial Mat Communities along an Oxygen Gradient in a Perennially Ice-Covered Antarctic Lake0 aMicrobial Mat Communities along an Oxygen Gradient in a Perennia c01/2016 a620 - 6300 v821 aJungblut, Anne, D.1 aHawes, Ian1 aMackey, Tyler, J.1 aKrusor, Megan1 aDoran, Peter, T.1 aSumner, Dawn, Y.1 aEisen, Jonathan, A.1 aHillman, Colin1 aGoroncy, Alexander, K.1 aStams, A., J. uhttp://aem.asm.org/lookup/doi/10.1128/AEM.02699-1504921nas a2200181 4500008004100000022001400041245008200055210006900137260001200206300001300218520434700231100002104578700001504599700002204614700002304636700002104659856005904680 2015 eng d a0091-761300aAntarctic microbial mats: A modern analog for Archean lacustrine oxygen oases0 aAntarctic microbial mats A modern analog for Archean lacustrine  c10/2015 aG36966.13 a

The evolution of oxygenic photosynthesis was the most important geochemical event in

Earth history, causing the Great Oxidation Event (GOE) ~2.4 b.y. ago. However, evidence is mixed as to whether O2 production occurred locally as much as 2.8 b.y. ago, creating O2 oases, or initiated just prior to the GOE. The biogeochemical dynamics of possible O2 oases have been poorly constrained due to the absence of modern analogs. However, cyanobacteria in microbial mats in a perennially anoxic region of Lake Fryxell, Antarctica, create a 1–2 mm O2-containing layer in the upper mat during summer, providing the first known modern analog for formation of benthic O2 oases. In Lake Fryxell, benthic cyanobacteria are present below the oxycline in the lake. Mat photosynthesis rates were slow due to low photon flux rate (1–2 μmol m-2 s-1) under thick ice cover, but photosynthetic O2 production was sufficient to sustain up to 50 μmol O2 L-1, sandwiched between anoxic overlying water and anoxic sedi- ments. We hypothesize that Archean cyanobacteria could have similarly created O2 oases in benthic mats prior to the GOE. Analogous mats may have been at least partly responsible for geological evidence of oxidative weathering prior to the GOE, and habitats such as Lake Fryxell provide natural laboratories where the impact of benthic O2 oases on biogeochemical signatures can be investigated. 

 

1 aSumner, Dawn, Y.1 aHawes, Ian1 aMackey, Tyler, J.1 aJungblut, Anne, D.1 aDoran, Peter, T. uhttp://geology.gsapubs.org/lookup/doi/10.1130/G36966.103959nas a2200205 4500008004100000022001400041245008900055210006900144260001200213300001600225490000700241520327000248100001403518700002303532700001503555700002303570700002103593700002203614856011703636 2015 eng d a0722-406000aCyanobacterial diversity in benthic mats of the McMurdo Dry Valley lakes, Antarctica0 aCyanobacterial diversity in benthic mats of the McMurdo Dry Vall c01/2015 a1097 - 11100 v383 a
Perennially ice-covered, meromictic lakes in the McMurdo Dry Valleys, Antarctica, are useful models to study the relationship between cyanobacterial and environmental variables. They have rich benthic cyanobacterial mat accumulations and stable stratification of physical and chemical conditions. Here, we evaluated cyanobacteria from benthic mats from multiple depths in three geographically separated ice-covered lakes, Lakes Vanda, Hoare and Joyce, using 16S rRNA gene clone libraries. We identified 19 ribotypes, mostly Oscillatoriales and several
Chroococcales, as well as potentially novel cyanobacterial ribotypes. The majority of ribotype diversity was shared between lakes, and only a weak relationship between ribotype community structure and environmental variables was evident. Multivariate analysis of all lake–depth combinations implied that photosynthetically active radiation, dissolved reactive phosphorus and conductivity were potentially important for shaping benthic communities in McMurdo Dry Valley lakes. Cyanobacterial-specific pigment signature analysis by high-performance liquid chromatography
showed that the cyanobacterial communities responded to light conditions similarly, irrespective of community composition. The results imply a capability within a suite of cyanobacteria to colonise, adapt and grow across broad environmental ranges and geographic space, and such adaptability may provide a high degree of community resistance and resilience to future climate-driven environmental change in Antarctic terrestrial aquatic
ecosystems.
1 aZhang, L.1 aJungblut, Anne, D.1 aHawes, Ian1 aAndersen, Dale, T.1 aSumner, Dawn, Y.1 aMackey, Tyler, J. uhttp://link.springer.com/10.1007/s00300-015-1669-0http://link.springer.com/content/pdf/10.1007/s00300-015-1669-0