Ethene (ETH)-grown inocula ofNocardioidesJS614 grow on vinyl chloride (VC), vinyl fluoride (VF), or vinyl bromide (VB) asthe sole carbon and energy source, with faster growth rates and higher cell yields on VC and VF than on VB. However, whereasacetate-grown inocula of JS614 grow on VC and VF after a lag period, growth on VB did not occur unless supplemental etheneoxide (EtO) was present in the medium. Despite inferior growth on VB, the maximum rate of VB consumption by ETH-growncells was ~ 50% greater than the rates of VC and VF consumption, but Br−release during VB consumption was non-stoichiometric with VB consumption (~ 66%) compared to 100% release of Cl−and F−during VC and VF consumption.Evidence was obtained for VB turnover-dependent toxicity of cell metabolism in JS614 with both acetate-dependent respirationand growth being significantly reduced by VB turnover, but no VC or VF turnover-dependent toxicity of growth was detected.Reduced growth rate and cell yield of JS614 on VB probably resulted from a combination of inefficient metabolic processing ofthe highly unstable VB epoxide (t0.5= 45 s), accompanied by growth inhibitory effects of VB metabolites on acetate-dependentmetabolism. The exact role(s) of EtO in promoting growth of alkene repressed JS614 on VB remains unresolved, with evidenceof EtO inducing epoxide consuming activity prior to an increase in alkene oxidizing activity and supplementing reductant supplywhen VB is the growth substrate.

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