Abstract
Heterotrophic bacteria are well known to be key players in the turnover of dissolved organic material (DOM) in the oceans, but the relationship between DOM uptake and bacterial clades is still not well understood. Here we explore the turnover and single-cell use of glucose, an amino acid mixture, N-acetylglucosamine (NAG), and protein by gammaproteobacterial clades in coastal waters of the West Antarctic Peninsula in summer and fall. More than 60% of the cells within two closely related gammaproteobacterial clades, Ant4D3 and Arctic96B-16, were active in using the amino acid mixture, protein, and NAG. In contrast, an average of only 7% of all SAR86 cells used amino acids and protein even in summer when DOM use was high. In addition to DOM uptake within a group, we explored the contribution of the three gammaproteobacterial groups to total community uptake of a compound. SAR86 contributed 5- to 10-fold less than the other gammaproteobacterial subgroups to the uptake of all compounds. We found that the overall contribution of the Ant4D3 clade to DOM uptake was highest, whereas the SAR86 clade contributed the least to DOM turnover in West Antarctic Peninsula waters. Our results suggest that the low growth activity of a bacterial clade leads to low abundance, fewer active cells and a low contribution to the turnover of DOM components.