Cloning and sequencing of a 2,5-dichloro-2,5-cyclohexadiene-1,4-diol dehydrogenase gene involved in the degradation of γ-hexachlorocyclohexane in Pseudomonas paucimobilis

In Pseudomonas paucimobilis UT26, γ-hexachlorocyclohexane (γ-HCH) is converted to 2,5-dichloro-2,5-cyclohexadiene-1,4-diol (2,5-DDOL), which is then metabolized to 2,5-dichlorohydroquinone. Here, we isolated from the genomic library of UT26 two genes which expressed 2,5-DDOL dehydrogenase activity when they were transformed into P. putida and Escherichia coli. Both gene products had an apparent molecular size of 28 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The first gene, named linC, located separately from the two genes (linA and linB) which we had already cloned as genes involved in the γ-HCH degradation. The other, named linX, located about 1 kb upstream of the linA gene encoding γ-HCH dehydrochlorinase. A γ-HCH degradation-negative mutant, named UT72, which lacked the whole linC gene but had the intact linX gene was isolated. The linC gene given in a plasmid could complement UT72. These results strongly suggest that the linC gene but not the linX gene is essential for the assimilation of γ-HCH in UT26. Deduced amino acid sequences of LinC and LinX show homology to those of members of the short-chain alcohol dehydrogenase family.