BACTERIAL OXIDATION OF METHYL-BROMIDE IN MONO LAKE, CALIFORNIA

The oxidation of methyl bromide (MeBr) in the water column of Mono Lak e, CA, was studied by measuring the formation of (HCO3)-C-14 from [C-1 4]MeBr. Potential oxidation was detected throughout the water column, with highest rates occurring in the epilimnion (5-12 m depth). The oxi dation of MeBr was eliminated by filter-sterilization, thereby demonst rating the involvement of bacteria. Vertical profiles of MeBr activity differed from those obtained for nitrification and methane oxidation, indicating that MeBr oxidation is not simply a co-oxidation process b y either nitrifiers or methanotrophs. Furthermore, specific inhibitors of methane oxidation and/or nitrification (e.g., methyl fluoride, ace tylene, allyl sulfide) had no effect upon the rate of MeBr oxidation i n live samples. Of a variety of potential electron donors added to Mon o Lake water, only trimethylamine resulted in the stimulation of MeBr oxidation. Cumulatively, these results suggest that the oxidation of M eBr in Mono Lake waters is attributable to trimethylamine-degrading me thylotrophs. Neither methyl chloride nor methanol inhibited the oxidat ion of [C-14]MeBr in live samples, indicating that these bacteria dire ctly oxidized MeBr rather than the products of MeBr nucleophilic subst itution reactions.