Comparative metagenomics of two shallow marine microbial communities in western Greenland

Metagenomic profiles of marine microbial communities from Greenlandic coastal waters remain scarce, despite the central role played by this region in discussions of global climate change. This study characterizes the taxonomic and functional structure of two near-shore shallow marine fjord mouth microbial communities from sites in western Greenland that differ in sea-surface temperatures, mean annual ice-coverage levels and annual glacial meltwater flux rates. Results indicate limited taxonomic and functional overlap between these two locations, with significant differences in the normalized abundance of 3372 species (25% of observed taxa) and 620 functional genes (49% of functional genes observed). At Sisimiut, a typical open-water “Baffin Bay” site characterized by moderate sea-surface temperatures, minimal annual sea-ice cover and limited glacial input, the metagenome is dominated by diverse chemolithotrophic taxa, including sulphate-reducing, nitrogen-fixing and methanogenic lineages. At the Ilulissat Icefjord, where low sea-surface temperatures, high turbidity, low salinity and strong glacial influences prevail, the community is less diverse and is dominated by psychrophilic (cold-adapted) bacteria such as Colwellia hornerae PAMC 20917. Functional profiles further distinguish these sites: the Ilulissat metagenome is enriched in genes common to ice-associated and cold-adapted metabolisms (e.g., exopolysaccharide biosynthesis, dimethyl-sulphide and dimethylsulfoniopropionate cycling), whereas these genes are comparatively rare at Sisimiut. Together, these data sets provide a descriptive baseline for these two sites and a framework for future comparative studies in the region.