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

Abstract

The natural biotic capacity of soils to degrade ␥-hexachlorocyclohexane (␥-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 ␥-HCH, which subsequently permitted isolation of a competent ␥-HCH-degrading microorganism. The decrease of ␥-HCH concurrently with the release of chloride ions and the production of CO 2 demonstrated the complete mineralization of ␥-HCH mediated by the isolate. This was confirmed by gas chromatography-mass spectrometry analyses showing that degradation subproducts of ␥-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 ␥-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 ␥-HCH degradative pathway appear to be extracellular and encoded by genes located on the chromosome, although numerous cryptic plasmids have been detected.

Presence of linA-Homologous DNA Sequences in Different Types of Soil and Their Sequence Diversity

“…The distribution of linA-harboring and γ-HCH-degrading Sphingobium in various types of soil in the world 1,7,12,27) supports this supposition.…”

“…linA is speculated to be a gene of foreign origin due to its low GC content compared with that of other lin genes in UT26 5,15) . Several other strains of γ-HCH-degrading Sphingobium isolated from soils in India 6,8,23) , France 2,27) , Spain 1,12) and Germany…”

Bioremediation of Hexachlorocyclohexane Contaminated Soil: Field Trials

“…Earlier studies suggested that degradation of HCH was faster under anoxic conditions and that microbial degradation was primary route of HCH disappearance from soil (MacRae et al, 1967). Microbial degradation of all the HCH-isomers has since been observed under oxic conditions both in soil (Bachmann et al, 1988 b); Doelman et al, 1985;Sahu et al, 1993) and in pure cultures of microorganisms Thomas et al, 1996). We have isolated in our laboratory a microbial consortium consisting of ten bacterial isolates which have got the capacity to degrade HCH (Manonmani et al, 2000;Murthy and Manonmani, 2007) under oxic conditions.…”

“…Degradation of HCH was faster under anoxic conditions and that microbial degradation was primary route of HCH disappearance from soil (MacRae et al, 1967). Microbial degradation of all the HCH-isomers has since been observed under oxic conditions both in soil (Bachmann et al, 1988 (a,b); Doelman et al, 1985;Sahu et al, 1993) and in pure cultures of microorganisms Thomas et al, 1996). Soil slurry has been adopted for the microbial degradation of pesticides, explosives, polynuclear aromatic hydrocarbons, and chlorinated organic pollutants (Gonzalez et al 2003).…”

Pseudomonas sp. to Sphingobium indicum: a journey of microbial degradation and bioremediation of Hexachlorocyclohexane

“…Later, both these strains were named as Sphingobium francense UT26 and Sphingobium indicum B90A [38]. Additionally bacterial strains, Rhodanobacter lindaniclasticus [39,40] and Sphingomonas paucimobilis Sp+ [41] were isolated from HCH contaminated soil in France. The three Sphingomonas strains were later reclassifi ed as distinct species of genus Sphingobium namely Sphingobium indicum B90A, Sphingobium japonicum UT26 and Sphingobium francense Sp + by using polyphasic taxonomical approach [38].…”