Metabolism of methyl bromide and dimethyl sulfide by marine bacteria isolated from coastal and open waters

Marine methylotrophic bacteria that consumed methyl bromide (MeBr) and/or dimethyl sulfide (DMS) were isolated: 4 strains from Long Island Sound, USA (LIS) and 1 from the tropical North Atlantic (TNA). Substrates used for enrichment were DMS, trimethylamine (TMA) or TMA plus MeBr. Attempts to obtain isolates on MeBr as the sole source of carbon and energy were unsuccessful. Three of the isolates used MeBr at rates that were higher than chemical loss, and one of these, isolated from coastal LIS, could use this C sub(1)-substrate for biomass production but only when other carbon sources were available simultaneously. Microbial consumption stopped when the MeBr concentration was higher than 0.5 mM and, similarly, when the DMS concentration was higher than 5 mM. The presence of DMS greatly enhanced MeBr consumption in cell suspensions. Inhibitor studies showed that DMS and MeBr were used by the same metabolic pathway in 2 LIS isolates, one of which displayed hydroxy-pyruvate reductase activity, indicative of the serine pathway of carbon assimilation. A third isolate obtained from the TNA that used MeBr did not use DMS, whereas 2 additional LIS strains isolated on DMS did not use MeBr. Therefore, MeBr utilization is not a common trait of DMS-degrading bacteria. MeBr concentrations in the marine environment are in the pM range and are the highest in coastal waters. This study indicates that growth on MeBr alone is unlikely to support bacterial growth and that removal of MeBr may be a cometabolic phenomenon. However, regardless of growth, consumption by marine bacteria may limit the flux of MeBr to the atmosphere.