The perennially ice-covered Lake Enigma, Antarctica supports unique microbial communities

Northern Foothills of Victoria Land, Antarctica contains numerous hydrological formations, ranging from small surface streams and ponds fed by glacial or snow meltwater to permafrost lakes containing briny pockets. Here we describe the discovery of a massive body of unfrozen stratified oligotrophic water in Lake Enigma, a permanently ice-covered lake previously thought to be frozen from top to bottom. A remarkable feature of the Lake Enigma microbial ecosystem is the presence, and sometimes even dominance, of ultrasmall bacteria belonging to the superphylum Patescibacteria, a group apparently absent from Antarctic lakes in the well-studied McMurdo Dry Valleys. Cyanobacteria are virtually absent from Lake Enigma ice and water column although they are well represented in its extensive and diverse benthic microbial mats. Collectively, these features reveal a new complexity in Antarctic lake food webs and demonstrate that in addition to phototrophic and simple chemotrophic metabolisms, both symbiotic and predatory lifestyles may exist. Unfrozen water in the perennially ice-covered Lake Enigma, Antarctica supports microbial communities distinct from those in other Antarctic lakes according to analyses of the lake’s physical structure, geochemistry, hydrological history, and microbiota.