Identification and Characterization of Genes Encoding a Putative ABC-Type Transporter Essential for Utilization of γ-Hexachlorocyclohexane in Sphingobium japonicum UT26

Sphingobium japonicum UT26 utilizes γ-hexachlorocyclohexane (γ-HCH) as its sole source of carbon and energy. In our previous studies, we cloned and characterized genes encoding enzymes for the conversion of γ-HCH to β-ketoadipate in UT26. In this study, we analyzed a mutant obtained by transposon mutagenesis and identified and characterized new genes encoding a putative ABC-type transporter essential for the utilization of γ-HCH in strain UT26. This putative ABC transporter consists of four components, permease, ATPase, periplasmic protein, and lipoprotein, encoded bylinK ,linL ,linM , andlinN , respectively. Mutation and complementation analyses indicated that all thelinKLMN genes are required, probably as a set, for γ-HCH utilization in UT26. Furthermore, the mutant cells deficient in this putative ABC transporter showed (i) higher γ-HCH degradation activity and greater accumulation of the toxic dead-end product 2,5-dichlorophenol (2,5-DCP), (ii) higher sensitivity to 2,5-DCP itself, and (iii) higher permeability of hydrophobic compounds than the wild-type cells. These results strongly suggested that LinKLMN are involved in γ-HCH utilization by controlling membrane hydrophobicity. This study clearly demonstrated that a cellular factor besides catabolic enzymes and transcriptional regulators is essential for utilization of xenobiotic compounds in bacterial cells.