Dynamics of Multiple lin Gene Expression in Sphingomonas paucimobilis B90A in Response to Different Hexachlorocyclohexane Isomers

ABSTRACT

Sphingomonas paucimobilis B90A is able to degrade the α-, β-, γ-, and δ-isomers of hexachlorocyclohexane (HCH). It contains the genes linA, linB, linC, linD, linE, and linR, which have been implicated in HCH degradation. In this study, dynamic expression of the lin genes was measured in chemostat-grown S. paucimobilis B90A by RNA dot blot hybridization and real-time reverse transcriptase PCR upon exposure to a pulse of different HCH isomers. Irrespective of the addition of HCH, linA, linB, and linC were all expressed constitutively. In contrast, linD and linE were induced with α-HCH (2 mg/liter) and γ-HCH (7 mg/liter). A sharp increase in mRNA levels for linD and linE was observed from 10 to 45 min after the addition of α- or γ-HCH. Induction of linD and linE was not detectable upon the addition of 0.7 mg of γ-HCH per liter, although the compound was degraded by the cells. The addition of β-HCH (5 mg/liter) or δ-HCH (20 mg/liter) did not lead to linE and linD induction, despite the fact that 50% of the compounds were degraded. This suggests that degradation of β- and δ-HCH proceeds by a different pathway than that of α- and γ-HCH.