Phylogenetic identification and metabolism of marine dimethylsulfide-consuming bacteria

Microbial consumption is one of the main processes, along with photolysis and ventilation, that remove the biogenic trace gas dimethylsulfide (DMS) from the surface ocean. Although a few isolates of marine bacteria have been studied for their ability to utilize DMS, little is known about the characteristics or phylogenetic affiliation of DMS consumers in seawater. We enriched coastal and open-ocean waters with different carbon sources to stimulate different bacterial communities (glucose-consuming bacteria, methyl group-consuming bacteria and DMS consumers) in order to test how this affected DMS consumption and to examine which organisms might be involved. Dimethylsulfide consumption was greatly stimulated in the DMS addition treatments whereas there was no stimulation in the other treatments. Analysis of microbial DNA by two different techniques (sequenced bands from DGGE gels and clone libraries) showed that bacteria grown specifically with the presence of DMS were closely related to the genus Methylophaga. We also followed the fate of consumed DMS in some of the enrichments. Dimethylsulfide was converted mostly to DMSO in glucose or methanol enrichments, whereas it was converted mostly to sulfate in DMS enrichments, the latter suggesting use of DMS as a carbon and energy source. Our results indicate that unlike the biochemical precursor of DMS, dimethylsulfoniopropionate (DMSP), which is consumed by a broad spectrum of marine microorganisms, DMS seems to be utilized as a carbon and electron source by specialists. This is consistent with the usual observation that DMSP turns over at much higher rates than DMS.