Linking a bacterial taxon to sulfur cycling in the sea:: Studies of the marine Roseobacter group

Evidence from culture-independent molecular studies indicate that members of the Roseobacter group are ubiquitous in marine environments, and bacteria in this taxon have now been isolated from and identified in systems as diverse as sea ice and coastal lagoons and as widespread as Antarctica and the Sargasso Sea. Because some members of this successful bacterial lineage are amenable to culturing, Roseobacter group isolates can be studied in the laboratory to reveal hints about potential ecological and biogeochemical roles. Initial studies of isolates suggested a widespread ability to degrade dimethylsulfoniopropionate (DMSP), an organic sulfur compound produced in abundance by marine algae. Further investigations revealed that some Roseobacter group isolates are able to carry out the major DMSP transformations that have been observed in natural bacterial communities from seawater. These include two competing pathways for DMSP degradation that may ultimately regulate the flux of organic sulfur (in the form of dimethylsulfide) from the surface ocean to the atmosphere, and a pathway for incorporation of the sulfur moiety of DMSP into bacterial protein. Recent field studies reinforce laboratory results, and demonstrate that members of the Roseobacter group may be one of the bacterial taxa linked to DMSP dynamics in the surface ocean.