Evidence for the presence of a CmuA methyltransferase pathway in novel marine methyl halide‐oxidizing bacteria

Summary Marine bacteria that oxidized methyl bromideand methylchloride were enriched and isolated from seawater samples. Six methyl halide-oxidizing enrichments were established from which 13 isolates that grew on methyl bromideand methylchloride as sole sources of carbon and energy were isolated and maintained. All isolates belonged to three different clades in the Roseobactergroup of the alpha subdivision of the Proteobacteriaand were distinct from Leisingeramethylohalidivorans, the only other identified marine bacterium that grows on methyl bromide  as sole source of carbon and energy. Genes  encoding the methyltransferase/ corrinoid-binding protein CmuA, which is responsible for the initial step of methylchloride oxidation in terrestrial methyl halide-oxidizing bacteria, were detected in enrichments and some of the novel marine strains. Gene clusters containing cmuA and other genes implicated in the metabolism of methyl halideswere cloned from two of the isolates. Expression of CmuA during growth on methyl halideswas demonstrated by analysis of polypeptides expressed during growth on methyl halidesby SDS-PAGE and mass spectrometry in two isolates representing two of the three clades. These findings indicate that certain marine methyl halidedegrading bacteria from the Roseobactergroup contain a methyltransferasepathway for oxidation of methyl bromidethat may be similar to that responsible for methylchloride oxidation in Methylobacteriumchloromethanicum. This pathway therefore potentially contributes to cycling of methyl halidesin both terrestrial and marine environments.