Linking the composition of bacterioplankton to rapid turnover of dissolveddimethylsulphoniopropionate in an algal bloom in the North Sea

The algal osmolyte, dimethylsulphoniopropionate (DMSP), is abundant in the surface oceans and is the major precursor of dimethyl sulphide (DMS), a gas involved in global climate regulation. Here, we report results from an in situ Lagrangian study that suggests a link between the microbially driven f luxes of dissolved DMSP (DMSPd) and specific members of the bacterioplankto n community in a North Sea coccolithophore bloom. The bacterial population in the bloom was dominated by a single species related to the genus Roseoba cter, which accounted for 24% of the bacterioplankton numbers and up to 50% of the biomass. The abundance of the Roseobacter cells showed significant paired correlation with DMSPd consumption end bacterioplankton production, whereas abundances of other bacteria did not. Consumed DMSPd (28 nM day(-1) ) contributed 95% of the sulphur end up to 15% of the carbon demand of the total bacterial populations, suggesting the importance of DMSP as a substra te for the Roseobacter-dominated bacterioplankton. In dominating DMSPd flux , the Roseobacter species may exert a major control on DMS production. DMSP d turnover rate was 10 times that of DMS (2.7 nM day(-1)), indicating that DMSPd was probably the major source of DMS, but that most of the DMSPd was metabolized without DMS production. Our study suggests that single species of bacterioplankton may at times be Important in metabolizing DMSP and regu lating the generation of DMS in the sea.