Aerobic Vinyl Chloride Metabolism in Groundwater Microcosms by Methanotrophic and Etheneotrophic Bacteria

Vinyl chloride (VC) is a carcinogen generated in groundwater by reductive dechlorination of chloroethenes. Under aerobic conditions, etheneotrophs oxidize ethene and VC, while VC-assimilators can use VC as their sole source of carbon and energy. Methanotrophs utilize only methane but can oxidize ethene to epoxyethane and VC to chlorooxirane. Microcosms were constructed with groundwater from the Carver site in MA containing these three native microbial types. Methane, ethene, and VC were added to the microcosms singly or as mixtures. In the absence of VC, ethene degraded faster when methane was also present. We hypothesized that methanotroph oxidation of ethene to epoxyethane competed with their use of methane, and that epoxyethane stimulated the activity of starved etheneotrophs by inducing the enzyme alkene monooxygenase. We then developed separate enrichment cultures of Carver methanotrophs and etheneotrophs, and demonstrated that Carver methanotrophs can oxidize ethene to epoxyethane, and that starved Carver etheneotrophs exhibit significantly reduced lag time for ethene utilization when epoxyethane is added. In our groundwater microcosm tests, when all three substrates were present, the rate of VC removal was faster than with either methane or ethene alone, consistent with the idea that methanotrophs stimulate etheneotroph destruction of VC.