Complete analysis of genes and enzymes for gamma- hexachlorocyclohexane degradation in Sphingomonas paucimobilis UT26

gamma-Hexachlorocyclohexane (gamma-HCH; also called BHC or lindane) is one of the highly chlorinated pesticides which can cause serious environmental problems. Sphingomonas paucimobilis UT26 degrades gamma-HCH under aerobic c onditions. The unique degradation pathway of gamma-HCH in UT26 is revealed. In the upstream pathway, gamma-HCH is transformed to 2,5-dichlorohydroquin one (2,5-DCHQ) by two different dehalogenases (LinA and LinB) and one dehyd rogenase (LinC) which are expressed constitutively. In the downstream pathw ay, 2,5-DCHQ is reductively dehalogenated, and then ring-cleaved by enzymes (LinD and LinE, respectively) whose expressions are regulated. We have clo ned and sequenced five structural genes (linA, linS, linC, linD, and linE) directly involved in this degradation pathway. The linD and linE genes form an operon, and its expression is positively regulated by the LysR-type tra nscriptional regulator (LinR). The genes linA, linB, and linC are constitut ively expressed, and are present separately from each other in the UT26 gen ome. Cell fractionation analysis, Western blotting, and immune electron mic roscopy revealed that LinA and LinB are localized in the periplasmic space of UT26.