Dissolved organic matter assimilation by heterotrophic bacterial groups in the western Arctic Ocean

Abundance of the major bacterial groups and dissolved organic matter (DOM) assimilation in the western Arctic Ocean were determined using fluorescence in situ hybridization (FISH) and microautoradiography combined with FISH (Micro-FISH). Cytophaga-like bacteria (25 to 65 %) and Alphaproteobacteria (17 to 40%) were the dominant bacterial groups, followed by Gammaproteobacteria (10 to 30 %). In contrast, Betaproteobacteria and Actinobacteria were never abundant. While the distribution of Alphaproteobacteria was relatively uniform along a transect from the shelf to the basin, Cytophaga-like bacteria were more abundant on the shelf and shelf-break. Similarly, the contribution to DOM assimilation by Cytophaga-like bacteria was highest on the shelf and lowest in the basin. In contrast, Alphaproteobacteria contributed the most to DOM assimilation at the slope. About 80 to 99 % of the variation in DOM assimilation was explained by bacterial group abundance. As a whole, the prokaryotic community was most active in assimilating free amino acids (50 to 60 %), followed by diatom-derived extracellular polymers (30 to 40 %) and protein (20 to 30 %). In contrast, relatively few cells assimilated glucose (10 to 20 %). This study revealed substantial variation in the abundance of major bacterial groups among the Arctic regions and in the assimilation of DOM components by these bacteria.