novel pathway for the biodegradation of γ-hexachlorocyclohexane by a Xanthomonas sp. strain ICH12

• Published in: Journal of applied microbiology Vol. 102; no. 6; pp. 1468 - 1478
• Main Authors: Manickam, N, Misra, R, Mayilraj, S
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-06-2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Base Sequence; Benzoquinones - metabolism; biodegradation; Biodegradation, Environmental; Biological and medical sciences; Cyclohexanes - metabolism; Fundamental and applied biological sciences. Psychology; Genes, Bacterial; Insecticides - metabolism; Lindane - metabolism; Metabolic Networks and Pathways; metabolites; Microbiology; Oxidoreductases - genetics; pathway; Polymerase Chain Reaction - methods; RNA, Bacterial - genetics; RNA, Ribosomal, 16S - genetics; Soil Microbiology; Sphingomonas paucimobilis; Xanthomonas; Xanthomonas - genetics; Xanthomonas - isolation & purification; Xanthomonas - metabolism; γ-hexachlorocylohexane; Pseudomonadales; Biodegradation; Applied microbiology; Metabolite; y-hexachlorocylohexane; Bacteria; Pseudomonadaceae; pathway; HCH; metabolites; Xanthomonas
• ISSN: 1364-5072; 1365-2672
• DOI: 10.1111/j.1365-2672.2006.03209.x

To isolate γ-hexachlorocyclohexane (HCH)-degrading bacteria from contaminated soil and characterize the metabolites formed and the genes involved in the degradation pathway. A bacterial strain Xanthomonas sp. ICH12, capable of biodegrading γ- HCH was isolated from HCH-contaminated soil. DNA-colony hybridization method was employed to detect bacterial populations containing specific gene sequences of the γ-HCH degradation pathway. linA (dehydrodehalogenase), linB (hydrolytic dehalogenase) and linC (dehydrogenase) from a Sphingomonas paucimobilis UT26, reportedly possessing γ-HCH degradation activity, were used as gene probes against isolated colonies. The isolate was found to grow and utilize γ-HCH as the sole carbon and energy source. The 16S ribosomal RNA gene sequence of the isolate resulted in its identification as a Xanthomonas species, and we designated it as strain ICH12. During the degradation of γ-HCH by ICH12, formation of two intermediates, γ-2,3,4,5,6-pentachlorocyclohexene (γ-PCCH), and 2,5-dichlorobenzoquinone (2,5-DCBQ), were identified by gas chromatography-mass spectrometric (GC-MS) analysis. While γ-PCCH was reported previously, 2,5-dichlorohydroquinone was a novel metabolite from HCH degradation. A Xanthomonas sp. for γ-HCH degradation from a contaminated soil was isolated. γ-HCH was utilized as sole source of carbon and energy, and the degradation proceeds by successive dechlorination. Two degradation products γ-PCCH and 2,5-DCBQ were characterized, and the latter metabolite was not known in contrasts with the previous studies. The present work, for the first time, demonstrates the potential of a Xanthomonas species to degrade a recalcitrant and widespread pollutant like γ-HCH. This study demonstrates the isolation and characterization of a novel HCH-degrading bacterium. Further results provide an insight into the novel degradation pathway which may exist in diverse HCH-degrading bacteria in contaminated soils leading to bioremediation of γ-HCH.