Cloning and Characterization of lin Genes Responsible for the Degradation of Hexachlorocyclohexane Isomers by Sphingomonas paucimobilis Strain B90

Abstract

Hexachlorocyclohexane (HCH) has been used extensively against agricultural pests and in public health programs for the control of mosquitoes. Commercial formulations of HCH consist of a mixture of four isomers, ␣, ␤, ␥, and ␦. While all these isomers pose serious environmental problems, ␤-HCH is more problematic due to its longer persistence in the environment. We have studied the degradation of HCH isomers by Sphingomonas paucimobilis strain B90 and characterized the lin genes encoding enzymes from strain B90 responsible for the degradation of HCH isomers. Two nonidentical copies of the linA gene encoding HCH dehydrochlorinase, which were designated linA1 and linA2, were found in S. paucimobilis B90. The linA1 and linA2 genes could be expressed in Escherichia coli, leading to dehydrochlorination of ␣-, ␥-, and ␦-HCH but not of ␤-HCH, suggesting that S. paucimobilis B90 contains another pathway for the initial steps of ␤-HCH degradation. The cloning and characterization of the halidohydrolase (linB), dehydrogenase (linC and linX), and reductive dechlorinase (linD) genes from S. paucimobilis B90 revealed that they share ϳ96 to 99% identical nucleotides with the corresponding genes of S. paucimobilis UT26. No evidence was found for the presence of a linE-like gene, coding for a ring cleavage dioxygenase, in strain B90. The gene structures around the linA1 and linA2 genes of strain B90, compared to those in strain UT26, are suggestive of a recombination between linA1 and linA2, which formed linA of strain UT26.

Biodegradation and bioremediation of pesticide in soil: concept, method and recent developments

“…In another example i.e. lindane [18], endosulfan [19,20], DDT [21] and monocrotophos [22,23], the microbes and/or enzymes were isolated and identifi ed. Genetic studies of microbial degradation indicates that the plasmids are the main place for the gene of interest usually spread throughout the microbial community.…”

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

“…All these sphingomonads have similar lin genes for HCH degradation. S. indicum B90A, S. francense Sp+ and S. japonicum UT26 have similar linA, linB, linC, linD, linE, linR and linF genes for γ-HCH degradation [8,46]. The rate of HCH degradation in S. francense Sp+ is similar to S. japonicum UT26 but all HCH isomers are degraded much more effi ciently by S. indicum B90A.…”

“…Sphingomonas paucimobilis B90A was found to contain two copies of linA gene [46]. A thorough analysis of two copies of linA revealed 88% amino acids similarity between them.…”

“…The C-terminal region of one of the linA gene in B90A was found to be replaced by 22 nucleotides of adjoining IS6100 element [8]. The two copies were named as linA1 and linA2 and while linA1 was found only in S. paucimobilis B90A, linA2 was 100% identical to that of S. paucimobilis UT26 and S. paucimobilis Sp+ [46]. Cloning and expression of these two gene revealed that linA1 re- tained the dehydrochlorinase activity even with the 22-nucleotide variation.…”

“…Although purifi ed preparation of LinB of strain UT26 transformed β-HCH to PCCH, crude cell incubation with strain UT26 had no affect on β-HCH transformation [60]. However, this was in contrast to B90A that was repeatedly found to degrade β-HCH [7,8,46,61]. This prompted us to look into the degradation of β-HCH by using purifi ed LinB of B90A as well as whole cell preparation of Sphingobium indicum B90A [62].…”