Diversity, abundance, and biomass production of bacterial groups in the western Arctic Ocean

To better understand links between the diversity and activity of bacterial communities in the Arctic Ocean, the surface waters of the Chukchi Sea were examined by clone library analysis and by a combination of fluorescence in situ hybridization (FISH) and microautoradiography. About 60% of the 16S rRNA sequences from the library had closest BLAST hits to bacteria found previously in the Arctic, and some of these sequences appear to be restricted to polar waters. The number of operational taxonomic units in the library dropped by more than half when sequences were grouped at 99% sequence similarity, indicating that the library was composed of several bacterial clusters with high sequence similarity. Oligonucleotide probes were designed to enumerate some bacterial groups found in the clone library such as the Arctic96B-16 cluster, Roseobacter RCA cluster, AGG58 cluster, and Polaribacter clade. FISH analyses revealed that each of these groups typically accounted for 3 to 10% of prokaryotes, while well known cosmopolitan groups like the SAR86 and SAR11 clades made up 8 and 25% of the prokaryotic communities, respectively. Overall, > 60% of total prokaryotes belonged to 8 specific bacterial groups, of which the SAR11 clade was the most diverse (< 13% 16S rRNA sequence difference). Together the Arctic96B-16, Roseobacter RCA, Polaribacter, and SARI 1 clades also accounted for 25 to 82% of biomass production at 4 locations, as determined by a combination of FISH and microautoradiography of H-3-leucine assimilation. These results indicate that community composition and biomass production in the western Arctic Ocean are dominated by a few bacterial groups.