Haloalkane dehalogenases other than LinB can contribute to the γ-hexachlorocyclohexane utilization

Haloalkane dehalogenases (HLDs) convert halogenated compounds to corresponding alcohols by a simple hydrolytic mechanism. Although many bacterial strains possess HLDs or HLD homologues, LinB is the only HLD known to be involved in the utilization of γ-hexachlorocyclohexane (γ-HCH), a man-made chlorinated pesticide. In this study, to gain insight into the functional evolution of HLDs toward γ-HCH utilization, the linB gene in γ-HCH-degrading Sphingobium japonicum strain UT26 was replaced by 7 other HLD or HLD homologous genes, including 3 putative ancestral enzymes. Interestingly, strains carrying genes for DmmA from a marine metagenome or Rluc_anc, an ancestor of Renilla-luciferin 2-monooxygenase and LinB, produced 2,5-dichlorophenol and 2,5-dichlorohydroquinone from γ-HCH, which are indicators of LinB activity, and grew in minimal medium supplied with γ-HCH as a sole carbon source. These results indicated that other HLDs, in addition to LinB, can play roles in the γ-HCH utilization.