02314nas 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<p>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 (O<sub>2</sub>). The microbial mats growing on the bottom of Lake Fryxell, Antarctica, have well-defined environmental gradients in PAR and (O<sub>2</sub>). 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 (O<sub>2</sub>) and PAR conditions: high (O<sub>2</sub>) and maximum PAR, variable (O<sub>2</sub>) with lower maximum PAR, and low (O<sub>2</sub>) 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 (O<sub>2</sub>) was saturated, PAR structured the community. In contrast, (O<sub>2</sub>) 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 (O<sub>2</sub>). The comprehensive metagenomic analysis suggests that the benthic microbial communities in Lake Fryxell are structured by energy flow across both meter- and millimeter-scales.</p>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/fiz207/569719602611nas 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<p>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.</p>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.1235302341nas a2200157   4500008004100000245017500041210006900216260001200285300001200297490000700309520168800316100001502004700001402019700002102033856012902054       2014                        eng d00aEstimating photosynthetic activity in microbial mats in an ice-covered Antarctic lake using automated oxygen microelectode profiling and variable chlorophyll fluorescence0 aEstimating photosynthetic activity in microbial mats in an iceco  c08/2014  a674-6880 v593 a An automated oxygen microprofiler measured a positive flux of oxygen from microbial mats in ice-covered Lake Hoare, Antarctica, from noon, at a photon flux of 20 µmol m−2 s−1, through to midnight (< 2 µmol photons m−2 s−1). Daily average oxygen flux was 200 µmol m−2 h−1; and, whereas it was maximal at noon, when a 10 mm broad concentration peak was observed 5 mm below the mat surface, flux correlated only weakly with irradiance. In contrast, relative electron transfer rate, estimated from variable chlorophyll fluorescence, suggested a linear relationship between photosystem activity and irradiance. This contradiction arose because of the conjunction of photosynthetic production of oxygen deep into these transparent, gelatinous mats (diel oxygen change was observed to 17 mm depth) and oxygen diffusion rates too slow to allow equilibration of oxygen concentration profiles with instantaneous production and consumption of oxygen. To confirm this, we developed a mathematical simulation of oxygen dynamics that included diffusion, photosynthesis, and respiration. The simulation further indicated that (1) net oxygen evolution is light limited is and confined to the upper few millimeters of the mat, (2) below 5–7 mm, respiration balanced photosynthesis, (3) below 17 mm, respiration and photosynthesis approached zero, even though organic carbon and dissolved oxygen were present, and (4) photosynthesis deep into the mat was dependent on high light transmission through the gelatinous matrix. These conclusions are consistent with current understanding of mat growth dynamics and point to approaches for long-term analysis of microbial mat productivity.1 aHawes, Ian1 aGiles, H.1 aDoran, Peter, T.  uhttps://mcm.lternet.edu/content/estimating-photosynthetic-activity-microbial-mats-ice-covered-antarctic-lake-using-automated00600nas a2200145   4500008004100000245011900041210006900160300001200229490000700241100001500248700002400263700001500287700002700302856012500329       2006                        eng d00aEnvironmental factors associated with deep chlorophyll maxima in dry valley lakes, South Victoria Land, Antarctica0 aEnvironmental factors associated with deep chlorophyll maxima in  a179-1890 v381 aBurnett, L1 aMoorhead, Daryl, L.1 aHawes, Ian1 aHoward-Williams, Clive  uhttps://mcm.lternet.edu/content/environmental-factors-associated-deep-chlorophyll-maxima-dry-valley-lakes-south-victoria