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Examines bacterioplankton-driven turnover of the algal osmolyte, dimethylsulphoniopropionate, and its degradation product, dimethylsulphide, in the North Sea. Fluorescence in situ hybridization; Findings of the stratification within the euphotic zone; Taxonomic identification of bacterioplankton and community structure; Relationship between bacterioplankton composition and production.

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 fluxes of dissolved DMSP (DMSPd) and specific members of the bacterioplankton community in a North Sea coccolithophore bloom. The bacterial population in the bloom was dominated by a single species related to the genus Roseobacter, 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 and bacterioplankton production, whereas abundances of other bacteria did not. Consumed DMSPd (28 nM day-1) contributed 95% of the sulphur and up to 15% of the carbon demand of the total bacterial populations, suggesting the importance of DMSP as a substrate for the Roseobacter-dominated bacterioplankton. In dominating DMSPd flux, the Roseobacter species may exert a major control on DMS production. DMSPd 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 regulating the generation of DMS in the sea. [ABSTRACT FROM AUTHOR]

Presents a study that examined virus concentrations through vertical profiles in a coccolithophore-dominated bloom in the North Sea using analytical flow cytometry (AFC). Methodology; AFC discrimination of viruses and bacteria; Results and discussion.

Describes the routes and rates of transformation of dimethylsulphoniopropionate to dimethyl sulphide (DMS) in a phytoplankton bloom in the North Sea. Sea to air flux of DMS; Key processes and sensitivity analysis; Information on grazer-mediated and bacteria-mediated DMS production.