Microbial diversity of perennially ice-covered Antarctic Lakes Enigma

The Northern Foothills area (Victoria Land, Antarctica) belongs to a rare group of ice-free desertic regions lying along the coast of an otherwise ice-burdened terrain. This area contains numerous hydrological formations, ranging from small surface streams and ponds fed by glacial or snow meltwater in the summer to permafrost lakes containing briny pockets. Here we described the discovery of a massive body of unfrozen stratified oligo-mineral water in Lake Enigma, which was previously thought to be completely frozen to the bottom. In addition to being most inaccessible of all known Antarctic subglacial freshwater lakes, due to ice cover that is more than three times thicker than the average of their ice sheets, Lake Enigma is among the deepest lakes in Victoria Land. This study examined physical structure, geochemistry, hydrological history and microbiota of Lake Enigma. We found distinct microbial assemblages occupying sub-habitats of the lake: surface ice, different lake depths and benthic microbial mats. The ice microbiota reflects modern transport and colonization of biota from terrestrial and marine landscapes, whereas planktonic and benthic assemblages more likely represent persistent remnant biota that emerged from an ancient ecosystem of the lake that froze. Another remarkable feature of the Lake Enigma ecosystem is the presence, and sometimes even dominance, of ultrasmall organisms belonging to the superphylum Patescibacteria, highlighting the previously overlooked complexity of food webs in Antarctic subglacial lakes with the symbiotic and predatory strategies existing there.