Characterization and analysis of three newly isolated hexachlorocyclohexane (HCH)-degrading strains

Three bacterial strains (designated as BHC-B, BHC-C, and BHC-D) that degrade γ-hexachlorocyclohexane (γ-HCH) were isolated and characterized. They were all identified as Sphingobium sp. according to the phylogenetic analysis of the 16S rRNA gene sequence and the physiologic and biochemical characteristics. Analysis with ERIC-PCR was first used to determine the similarities of the different Sphingobium strains. Strains BHC-B, BHC-C, and BHC-D could also degrade three other HCH isomers (α-, β-, and δ-isomer), and the degradation rates were in the following order: γ-HCH > α-HCH > δ-HCH > β-HCH. For the same isomer, the degradation rates of the three HCH-degrading strains were in the order: BHC-C > BHC-B > BHC-D. These three strains had six key lin genes (linA, linB, linC, linD, linE, linR). The sequence similarities of linA, linC, linD, linE, and linR were 99%-100% and highly conserved at the amino acid level. By contrast, the LinB sequence diverged by 2%-3%, which might be responsible for the difference of the degradation rate in different strains against the same HCH isomer. However, further studies are needed to prove this hypothesis.