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

Abstract

ABSTRACT Polaromonas sp. strain JS666 grows on cis -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 for c 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 of c DCE degradation. Both the transient accumulation of dichloroacetaldehyde in c DCE-degrading cultures and dichloroacetaldehyde dehydrogenase activities in cell extracts of JS666 support a pathway for degradation of c DCE through dichloroacetaldehyde. The mechanism minimizes the formation of c DCE epoxide. The molecular phylogeny of the cytochrome P450 gene and the organization of neighboring genes suggest that the c 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.