Mineralization of .alpha.-, .gamma.-, and .beta.-Isomers of Hexachlorocyclohexane by a Soil Bacterium under Aerobic Conditions

Abstract

The degradation of uniformly 14C-labeled isomers (a, y , and P) of hexachlorocyclohexane (HCH), added separately to a mineral salts medium as a sole source of carbon, by a soil bacterium, Pseudomonas sp., under aerobic conditions was studied. During aerobic degradation, about 10-12% of the 14C in a-and y-HCH was accounted for as 14C02 as compared to 5% from P-HCH. Most of the 14C in a-and y-HCH accumulated as water-soluble products, while formation of water-soluble products from P-HCH was negligible. Almost all of the 14C in the three isomers of HCH was accounted for in different fractions (Con, chloroform-diethyl ether, water phase) following bacterial degradation under aerobic conditions. GC-MS analysis of P-HCH residues in the chloroformdiethyl ether extract suggested the formation of pentachlorocyclohexanol and tetrachlorocyclohexanediol as products of aerobic metabolism of P-HCH.

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

“…was isolated from sugarcane fi elds in India [7] and this was the fi rst report of aerobic degradation of even β-HCH by a bacterium. Later, both these strains were named as Sphingobium francense UT26 and Sphingobium indicum B90A [38].…”

“…As mentioned earlier, Sahu et al (1990) [7] were the fi rst to isolate Pseudomonas sp., a HCH-degrader from an Indian sugarcane fi eld which was later classifi ed as Sphingobium indicum B90A by polyphasic approach [38]. …”

“…By 2000, studies on Sphingomonas paucimobilis B90A isolated by Sethunathan and coworkers made it apparent that it has a better potential for HCH degradation [45] as compared to the then known HCH degrading strains. Sethunathan and his colleagues had indicated this in their pioneering study [45] at a time when molecular genetics involved in the degradation of even γ-HCH was not understood very clearly.…”

“…Sethunathan and his colleagues had indicated this in their pioneering study [45] at a time when molecular genetics involved in the degradation of even γ-HCH was not understood very clearly. Until 2004 reports that appeared on HCH degradation by Nagata and coworkers [44] suggested that UT26 degrades only α-, δ-, and γ-HCH (till then it was not known that UT26 also degrades β-HCH) and contains linA, linB, linC and linDER genes that encode HCH dehydrochlorinase, haloalkane dehalogenase, dehalogenase and ring cleavage dioxygenase leading to the conversion of γ-HCH to pentachlorocyclohexene, dichlorocyclohexadiene, dichlorohydroquinone, chlorohydroquinone, hydroquinone, acyclchloride, γ-hydroxymuconic acid and maleylacetate.…”

“…The fi rst bacterial strain found to degrade four isomers of HCH (α, β, γ, and δ) was Pseudomonas sp. (now Sphingobium indicum B90A), which was isolated by Sethunathan and coworkers in 1990 from sugarcane fi elds in India [7]. This was the fi rst report on microbial degradation of the most recalcitrant β isomer of HCH.…”