Cloning and sequencing of a 2,5-dichlorohydroquinone reductive dehalogenase gene whose product is involved in degradation of γ- hexachlorocyclohexane by Sphingomonas paucimobilis

Sphingomonas (formerly Pseudomonas) paucimobilis UT26 utilizes Υ- hexachlorocyclohexane (γ-HCH), a halogenated organic insecticide, as a sole carbon and energy source. In a previous study, we showed that Υ-HCH is degraded to 2,5-dichlorohydroquinone (2,5-DCHQ) (Y. Nagata, R. Ohtomo, K. Miyauchi, M. Fukuda, K. Yano, and M. Takagi, J. Bacteriol. 176:3117-3125, 1994). In the present study, we cloned and characterized a gene, designated linD, directly involved in the degradation of 2,5-DCHQ. The linD gene encodes a peptide of 343 amino acids and has a low level of similarity to proteins which belong to the glutathione S-transferase family. When Lind was overproduced in Escherichia coli, a 40-kDa protein was found after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Northern blot analysis revealed that expression of the linD gene was induced by 2,5-DCHQ in 8. paucimobilis UT26. Thin-layer chromatography and gas chromatography-mass spectrometry analyses with the LinD-overexpressing E. coli cells revealed that Lind converts 2,5-DCHQ rapidly to chlorohydroquinone (CHQ) and also converts CHQ slowly to hydroquinone. Lind activity in crude Cell extracts was increased 3.7-fold by the addition of glutathione. All three of the Tn5- induced mutants of UT26, which lack 2,5-DCHQ dehalogenase activity, had rearrangements or a deletion in the lind region. These results indicate that LinD is a glutathione-dependent reductive dehalogenase involved in the degradation of Υ-HCH by S. paucimobilis UT26.