Abstract
Summary Commercial formulations of hexachlorocyclohexane (HCH) consist of a mixture of four isomers, α, β, γ and δ. All these four isomers are toxic and recalcitrant pollutants. Sphingobium (formerly Sphingomonas ) sp. strain BHC‐A is able to degrade all four HCH isomers. Eight lin genes responsible for the degradation of γ‐HCH in BHC‐A were cloned and analysed for their role in the degradation of δ‐HCH, and the initial conversion steps in δ‐HCH catabolism by LinA and LinB in BHC‐A were found. LinA dehydrochlorinated δ‐HCH to produce 1,3,4,6‐tetrachloro‐1,4‐cyclohexadiene (1,4‐TCDN) via δ‐pentachlorocyclohexene (δ‐PCCH). Subsequently, both 1,4‐TCDN and δ‐PCCH are catalysed by LinB via two successive rounds of hydrolytic dechlorinations to form 2,5‐dichloro‐2,5‐cyclohexadiene‐1,4‐diol (2,5‐DDOL) and 2,3,5‐trichloro‐5‐cyclohexene‐1,4‐diol (2,3,5‐TCDL) respectively. LinB could also catalyse the hydrolytic dechlorination of δ‐HCH to 2,3,5,6‐tetrachloro‐1,4‐cyclohexanediol (TDOL) via 2,3,4,5,6‐pentachlorocyclohexanol (PCHL).