Bacterial Biodiversity in Permanently Ice-covered Lakes of the McMurdo Dry Valleys, Antarctica

Abstract

The ice-covered lakes of the McMurdo Dry Valleys (MDVs) are widely acknowledged as one of the extreme habitats on Earth. Permanently cold temperatures, saline waters and extended periods of darkness in these aquatic ecosystems are considered limiting factors for life. Despite these environmental constraints, certain microorganisms thrive in these harsh-icy environments. To better understand the distribution and diversity of prokaryotes (Bacteria), we conducted 454-sequencing of the 16S rRNA gene on 69 samples collected from distinct depths in four lakes of the MDVs in November and December in 2012: Lake Fryxell (FRX), Lake Miers (MIE), West (WLB) and East (ELB) lobes of Lake Bonney. A total of 1,903 operational taxonomic units (OTUs) were generated from approximately 162,931 sequence reads with 97% similarity cutoff. Sequence reads were clustered into 49 phyla with FRX being the most diverse habitat and WLB the least diverse. Bacteroidetes (30.8%) and Actinobacteria (23%) were the most dominant phylum across all samples followed by Proteobacteria (17.5%), especially the Beta- and Deltaproteobacteria in FRX and Gammaproteobacteria in Bonney. These data show that highly heterogeneous bacterial communities exist among lakes at the phylum level. Statistical analyses demonstrate that community composition was most closely related to water column geochemistry with particular taxonomic groups inhabiting specific layers in the water columns.