Bacteriophages in Antarctic subglacial lakes reveal novel biodiversity and biogeochemical potential.

Of the more than 600 subglacial lakes identified in Antarctica thus far, Whillans Subglacial Lake and Mercer Subglacial Lake are the only lakes to have been directly and cleanly sampled. Although hydrologically isolated from direct marine contact for approximately 6.3 ± 1.0 ka, both lakes periodically discharge into the Ross Ice Shelf marine cavity. We present the first direct characterization of bacteriophages in Antarctic subglacial lakes, combining microscopy, metagenomics, and gene-sharing network analyses with bacteriophages found in the Ross Ice shelf marine cavity. The data reveal that bacteriophages are less abundant than their microbial hosts, with virus to prokaryote ratios below those of typical oligotrophic environments. Eight hundred sixty-one double-stranded DNA viral contigs were recovered forming 66 distinct viral clusters; only 18.4% could be identified at ≥85% sequence similarity in the IMG/VR database, showing high genetic novelty. The data showed 114 putative auxiliary metabolic genes involved in nutrient cycling and DNA methylation, and we predicted hosts spanning 13 prokaryotic classes. Several genetic clusters were shared with Antarctic subglacial lakes and Ross Ice Shelf cavity, indicating ecological connectivity that may extend the influence of subglacial phages to carbon and nutrient cycling in downstream Antarctic coastal ecosystems.