Benthic microbial community structure and ecological functions along the salinity gradient in the East Siberian Sea

The rising temperature in the Arctic changes marine environments such as sea ice fluctuation, primary production, and riverine input and these changes, in turn, impact on benthic ecosystems. East Siberian Sea (ESS) represents shallow shelf seas with three to seven times higher river discharge than other seas of Russian Arctic. However, studies on the microbial composition and functions according to the environmental parameters have not been performed in the ESS. In this study, the benthic microbial community structure with the environmental parameters and their ecological functions were investigated. Bacterial community was dominated by the phyla Proteobacteia (51.1±6.6%) followed by Bacteroidetes (16.4±9.5%), Planctomycetes (8.9±3.8%), Acidobacteria (6.5±4.2%), Actinobacteria (2.6±2.0%). In the archaeal community, Thaumarchaeota (70.9±11.1%) and Euryarchaeota (27.7±11.4%) were predominant. There are some microbial taxa showing significant changing pattern along the latitude. The proportion of Alphaproteobacteria and Acidobacteria increased while that of Bacteroidetes and Deltaproteobacteria and Thaumarchaeota decreased along the latitude. Microbial community composition and function of major taxa were clearly differentiated according to the latitude and concurrent environmental parameters such as salinity and concentration of ammonium and sulfate. In addition, the function of major microbial taxa including ammonium oxidation and sulfate reduction inferred from 16S rRNA identity also changed across the salinity gradient. These results imply that environmental changes in the benthic ecosystems accelerated from the climate change may impact a significant change on benthic microbial community composition and their functions.