Viruses in Subglacial Antarctic Lake Environments

Abstract:

Active hydrological systems beneath the Antarctic ice sheet include lakes, rivers, streams and water saturated sediments that form the basis for subglacial ecosystems. Of the ~400 subglacial lakes identified in Antarctica, Whillans Subglacial Lake (SLW) and Mercer Subglacial Lake (SLM) have been sampled directly using clean access technology over the last decade. SLW and SLM are lie beneath 800 m and 1100 m of ice, respectively, near the Siple Coast of West Antarctica and have been isolated from direct exchange with surface environments for more than 10,000 years. The lakes have water temperatures between -0.75 and 0. 2 ˚C. These lakes support diverse microbial ecosystems that derive their carbon and energy through chemolithoautotrophy and consumption of relict organic matter from past marine deposition. We assessed the viral assemblages in these environments using metagenomic sequencing of genomic DNA and microscopic analysis. In SLM, free living virus-like particles (VLPs) (1.0 × 10⁴ VLPs ml^-1) were within the same order of magnitude of prokaryotic cell concentration in the water column of SLM (2.1 × 10⁴ cells mL^-1). Over 120 DNA bacteriophage populations were identified in viromes derived from SLW and SLM. Potential virus hosts correlated with the most abundant bacterial taxa in the lake water columns and sediments, suggesting the possibility for phage-host relationship. Beta-diversity indicates that the viral communities in SLW and SLM were distinct when compared to other Antarctic surface lake environments and those found in the global ocean viral database. Our data are the first to describe viral communities beneath the West Antarctic Ice Sheet and support the possibility for top-down control by bacteriophages in Antarctic subglacial aquatic ecosystems.