Remarkably diverse and contrasting archaeal communities in a large arctic river and the coastal Arctic Ocean

Although the microbial biodiversity of arctic seas has received an increasing amount of attention, little is known about the microbial communities of its inflowing rivers. In this study we examined the molecular diversity of Archaea in the largest arctic river in North America, the Mackenzie River, and in the adjacent coastal Beaufort Sea (Canadian Arctic) during maximum open water conditions (October 2002). The Mackenzie River 16S rRNA clone libraries revealed a remarkably diverse assemblage of archaeal sequences, with an estimated 286 phylotypes defined as sequences with 97% similarity. These grouped mainly within 2 phylogenetic clusters, and were related to sequences earlier retrieved from flooded soils and sediments previously named RC-V and LDS. The marine coastal libraries were of very different composition to those of river libraries and were dominated by Group II Euryarchaeota followed by Group I Crenarchaeota. These coastal assemblages had greater archaeal diversity (18 to 23 phylotypes) than previously reported for marine communities elsewhere, and differed from previously described central Arctic Ocean assemblages. This may reflect the heterogeneous mixture of organic substrates and particles available for microbial heterotrophy in arctic coastal waters and the use of an alternative primer pair (109f-915r) in this study. The coastal sequences grouped within typical marine clusters, and we therefore conclude that they were an active autochthonous community rather than one derived from the large inflowing river. These results underscore the rich microbial diversity in arctic rivers and their adjacent coastal marine ecosystems.