ISOLATION AND CHARACTERIZATION OF A NOVEL GAMMA-HEXACHLOROCYCLOHEXANE-DEGRADING BACTERIUM

The natural biotic capacity of soils to degrade gamma-hexachlorocycloh exane (gamma-HCH, lindane) was estimated using an enrichment technique based on the ability of soil bacteria to develop on synthetic media a nd degrade the xenobiotic compound, used as the sole source of carbon and energy. Bacterial inocula from relatively highly contaminated soil s (from wood treatment factories) were found to promote efficiently th e degradation of gamma-HCH, which subsequently permitted isolation of a competent gamma-HCH-degrading microorganism. The decrease of gamma-H CH concurrently with the release-of chloride ions and the production o f CO2 demonstrated the complete mineralization of gamma-HCH mediated b y the isolate. This was confirmed by gas chromatography-mass spectrome try analyses showing that degradation subproducts of gamma-HCH include d an unidentified tetrachlorinated compound and subsequently 1,2,4-tri chlorobenzene and 2,5-dichlorophenol. The two linA- and linB-like gene s coding, respectively, for a gamma-HCH dehydrochlorinase and a dehalo genase were characterized by using a PCR strategy based on sequence ho mologies with previously published sequences from Sphingomonas paucimo bilis UT26. Nucleotide sequence analysis of the linA-like region revea led the presence of a 472-bp open reading frame exhibiting high homolo gy with the linA gene from S. paucimobilis, while a preliminary study also indicated strong homology among the two linB genes. All enzymes i nvolved in the gamma-HCH degradative pathway appear to be extracellula r and encoded by genes located on the chromosome, although numerous cr yptic plasmids have been detected.