Constitutive expression of pMMO by Methylocystis strain SB2 when grown on multi-carbon substrates: implications for biodegradation of chlorinated ethenes.

The particulate methane monooxygenase (pMMO) in Methylocystis strain SB2 was found to be constitutively expressed in the absence of methane when the strain was grown on either acetate or ethanol. Real-time quantitative polymerase chain reaction (PCR) and reverse transcription-PCR showed that the expression of pmoA decreased by one to two orders of magnitude when grown on acetate as compared with growth of strain SB2 on methane. The capability of strain SB2 to degrade a mixture of chlorinated ethenes in the absence of methane was examined to verify the presence and activity of pMMO under acetate-growth conditions as well determine the effectiveness of such conditions for bioremediation. It was found that when strain SB2 was grown on acetate and exposed to 40 µM each of trichloroethylene (TCE), trans-dichloroethylene (t-DCE) and vinyl chloride (VC), approximately 30% of VC and t-DCE was degraded but no appreciable TCE removal was measured after 216 h of incubation. The ability to degrade VC and t-DCE was lost when acetylene was added, confirming that pMMO was responsible for the degradation of these chlorinated ethenes by Methylocystis strain SB2 when the strain was grown on acetate.