Niche specialization of bacteria in permanently ice-covered lakes of the McMurdo Dry Valleys, Antarctica

Abstract

Perennially ice-covered lakes in the McMurdo Dry Valleys are chemically stratified with depth and have distinct biological gradients. Despite the long-term studies on these unique environments there remains a paucity of data on microbial community structure in the water columns of these lakes. We investigated bacterial diversity in five different ice-covered Antarctic lakes using 16S rRNA gene-based pyrosequencing. Distinct communities were present in each lake, paralleling the unique biogeochemical characteristics of each environment. Certain bacterial lineages were confined exclusively to a specific depth of each lake. For example, Candidate division WM88 occurred at 15 m depth of Lake Fryxell solely, while unknown lineages of Chlorobi are found only at the depth of 18 m in Lake Miers. The 30 m depth of East and West Lobe Bonney was occupied by two distinct Firmicutes classes. Redundancy analysis revealed that community variation of bacterioplankton was explained by the different chemistries unique to each lake and depth. In particular, assemblages from deeper layers beneath the chemocline had distinct biogeochemical associations differing from those of the upper layers. These patterns of community composition may represent bacterial adaptations to the extreme and unique biogeochemical gradients of ice-covered lakes in the McMurdo Dry Valleys.