An annual cycle of dimethylsulfoniopropionate-sulfur and leucine assimilating bacterioplankton in the coastal NW Mediterranean

13 pages, 6 figuresThe contribution of major phylogenetic groups to heterotrophic bacteria assimilating sulfur from dissolved dimethylsulfoniopropionate (DMSP) and assimilating leucine was analysed in surface seawaters from Blanes Bay (NW Mediterranean) over an annual study between March 2003 and April 2004. The percentage of bacteria assimilating DMSP-S showed a strong seasonal pattern, with a steady increase from winter (8 ± 5%) to summer (23 ± 3%). The same seasonal pattern was observed for the rate of DMSP-S assimilation. The annual average percentage of DMSP-S-assimilating bacteria (16 ± 8%) was lower than the corresponding percentage of leucine-assimilating cells (35 ± 16%), suggesting that not all bacteria synthesizing protein incorporated DMSP-S. Smaller differences between both percentages were recorded in summer. Members of the Alphaproteobacteria (Roseobacter and SAR11) and Gammaproteobacteria groups accounted for most of bacterial DMSP-S-assimilating cells over the year. All major bacterial groups showed an increase of the percentage of cells assimilating DMSP-S during summer, and contributed to the increase of the DMSP-S assimilation rate in this period. In these primarily P-limited waters, enrichment with P + DMSP resulted in a stimulation of bacterial heterotrophic production comparable to, or higher than, that with P + glucose in summer, while during the rest of the year P + glucose induced a stronger response. This suggested that DMSP was more important a S and C source for bacteria in the warm stratified season. Overall, our results suggest that DMSP-S assimilation is controlled by the contribution of DMSP to S (and C) sources rather than by the phylogenetic composition of the bacterioplanktonThis work was supported by the Spanish Ministry of Education and Science through a PhD studentship to M.V.-C, and through the projects MicroDIFF and MODIVUS (contracts REN2001-2120/MAR anc DTM2005-04795/MAR to J.M.G), by the Catalan government through Grant 2005SGR00021 (to R.S.) and by th EU's 5th Framework Program through project BASICs (contract EVK3-CT-2002-00078 to J.M.G.)Peer reviewe