Isolation and characterization of a novel gamma-hexachlorocyclohexane-degrading bacterium

The natural biotic capacity of soils to degrade gamma-hexachlorocyclohexane (gamma-HCH, lindane) was estimated using an enrichment technique based on the ability of soil bacteria to develop on synthetic media and degrade the xenobiotic compound, used as the sole source of carbon and energy. Bacterial inocula from relatively highly contaminated soils (from wood treatment factories) were found to promote efficiently the degradation of gamma-HCH, which subsequently permitted isolation of a competent gamma-HCH-degrading microorganism. The decrease of gamma-HCH concurrently with the release-of chloride ions and the production of CO2 demonstrated the complete mineralization of gamma-HCH mediated by the isolate. This was confirmed by gas chromatography-mass spectrometry analyses showing that degradation subproducts of gamma-HCH included an unidentified tetrachlorinated compound and subsequently 1,2,4-trichlorobenzene and 2,5-dichlorophenol. The two linA- and linB-like genes coding, respectively, for a gamma-HCH dehydrochlorinase and a dehalogenase were characterized by using a PCR strategy based on sequence homologies with previously published sequences from Sphingomonas paucimobilis UT26. Nucleotide sequence analysis of the linA-like region revealed the presence of a 472-bp open reading frame exhibiting high homology with the linA gene from S. paucimobilis, while a preliminary study also indicated strong homology among the two linB genes. All enzymes involved in the gamma-HCH degradative pathway appear to be extracellular and encoded by genes located on the chromosome, although numerous cryptic plasmids have been detected.