Abstract
Lake Vostok, the 7th largest (by volume) and 4th deepest lake on Earth, is covered by more than 3,700 m of ice, making it the largest subglacial lake known. The combination of cold, heat (from possible hydrothermal activity), pressure (from the overriding glacier), limited nutrients and complete darkness presents extreme challenges to life. Here, we report metagenomic/metatranscriptomic sequence analyses from four accretion ice sections from the Vostok 5G ice core. Two sections accreted in the vicinity of an embayment on the southwestern end of the lake, and the other two represented part of the southern main basin. We obtained 3,507 unique gene sequences from concentrates of 500 ml of 0.22 µm-filtered accretion ice meltwater. Taxonomic classifications (to genus and/or species) were possible for 1,623 of the sequences. Species determinations in combination with mRNA gene sequence results allowed deduction of the metabolic pathways represented in the accretion ice and, by extension, in the lake. Approximately 94% of the sequences were from Bacteria and 6% were from Eukarya. Only two sequences were from Archaea. In general, the taxa were similar to organisms previously described from lakes, brackish water, marine environments, soil, glaciers, ice, lake sediments, deep-sea sediments, deep-sea thermal vents, animals and plants. Sequences from aerobic, anaerobic, psychrophilic, thermophilic, halophilic, alkaliphilic, acidophilic, desiccation-resistant, autotrophic and heterotrophic organisms were present, including a number from multicellular eukaryotes.
Highlights
Lake Vostok is the largest of nearly 400 subglacial lakes that have been found in Antarctica [1,2,3,4,5], at least some of which are connected by subglacial rivers and streams [6]
For the present metagenomic/metatranscriptomic study, we examined two ice core sections that accreted in the vicinity of the embayment, and two ice core sections that accreted over the southern main lake basin
A total of 3,369 unique sequences were derived from V5, of which 1,543 could be taxonomically classified (Figure 1; Tables S1, S2, S3, S4, S5, S6), and 138 unique assembled sequences were derived from V6, of which 80 could be taxonomically classified (Figure 1; Tables S7, S8, S9, S10)
Summary
Lake Vostok is the largest of nearly 400 subglacial lakes that have been found in Antarctica [1,2,3,4,5], at least some of which are connected by subglacial rivers and streams [6]. Ice that accreted in the vicinity of the embayment has relatively high concentrations of ions, organic carbon, biomass and mineral inclusions (termed ‘‘type I’’ – or type 1 - accretion ice) [8], [10], [11]. Over the majority of the lake, the accretion ice contains far fewer mineral inclusions, as well as lower concentrations of ions, organic carbon, and biomass [8], [10], [11]. This relatively clear ice is known as ‘‘type II’’ (or type 2) accretion ice
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