Project description:Dimethylsulfide is a volatile organic sulfur compound that provides the largest input of biogenic sulfur from the oceans to the atmosphere, and thence back to land, constituting an important link in the global sulfur cycle. Microorganisms degrading DMS affect fluxes of DMS in the environment, but the underlying metabolic pathways are still poorly understood. Methylophaga thiooxydans is a marine methylotrophic bacterium capable of growth on DMS as sole source of carbon and energy. Using proteomics and transcriptomics we identified genes expressed during growth on dimethylsulfide and methanol to refine our knowledge of the metabolic pathways that are involved in DMS and methanol degradation in this strain. Amongst the most highly expressed genes on DMS were the two methanethiol oxidases driving the oxidation of this reactive and toxic intermediate of DMS metabolism. Growth on DMS also increased expression of the enzymes of the tetrahydrofolate linked pathway of formaldehyde oxidation, in addition to the tetrahydromethanopterin linked pathway. Key enzymes of the inorganic sulfur oxidation pathway included flavocytochrome c sulfide dehydrogenase, sulfide quinone oxidoreductase, and persulfide dioxygenases. A sulP permease was also expressed during growth on DMS. Other enzymes of organic and inorganic sulfur metabolism previously detected in cell extracts of Methylophaga have not been characterised at the genetic level yet; their expression level and regulation could not be analysed. A pan-genome analysis of six available Methylophaga genomes suggests that only two of the six investigated bacteria have the metabolic potential to utilize methanethiol, the degradation product of DMS. These results mirror phenotypic analyses and demonstrate that DMS-utilization and subsequent C1 and sulfur oxidation are not conserved across the entire genus.
