Cytochrome P450 Initiates Degradation ofcis-Dichloroethene by Polaromonas sp. Strain JS666

Polaromonas sp. strain JS666 grows oncis -1,2-dichoroethene (c DCE) as the sole carbon and energy source under aerobic conditions, but the degradation mechanism and the enzymes involved are unknown. In this study, we established the complete pathway forc DCE degradation through heterologous gene expression, inhibition studies, enzyme assays, and analysis of intermediates. Several lines of evidence indicate that a cytochrome P450 monooxygenase catalyzes the initial step ofc DCE degradation. Both the transient accumulation of dichloroacetaldehyde inc DCE-degrading cultures and dichloroacetaldehyde dehydrogenase activities in cell extracts of JS666 support a pathway for degradation ofc DCE through dichloroacetaldehyde. The mechanism minimizes the formation ofc DCE epoxide. The molecular phylogeny of the cytochrome P450 gene and the organization of neighboring genes suggest that thec DCE degradation pathway recently evolved in a progenitor capable of degrading 1,2-dichloroethane either by the recruitment of the cytochrome P450 monooxygenase gene from an alkane catabolic pathway or by selection for variants of the P450 in a preexisting 1,2-dichloroethane catabolic pathway. The results presented here add yet another role to the broad array of productive reactions catalyzed by cytochrome P450 enzymes.