Rapid degradation of lindane (γ-hexachlorocyclohexane) at low temperature by Sphingobium strains

Bioremediation of anthropogenic organic pollutants in cold climates is often limited by lower microbial or enzyme activity induced by low temperature. The present study addressed this issue through the degradation of γ-hexachlorocyclohexane (γ-HCH) by three Sphingobium strains (S. indicum B90A, S. japonicum UT26 and S. francense Sp+) under low temperature (4 °C). After 5 days incubation at 4 °C, 79.7% and 43.8% of 5 and 25 mg L^-1 of γ-HCH added were degraded, respectively by the inoculation of 1.75 × 10⁷ cells mL^-1 of S. indicum B90A. An increase in inoculum concentration to 1.72 × 10⁸ cells mL^-1 significantly increased the degradation to 98.1 ± 1.7% of 5 mg L^-1 within 24 h. Further, S. indicum B90A and S. japonicum UT26 can rapidly degrade γ-HCH at 4 °C, while the degradation capability of S. francense Sp+ is relatively low. At 4 °C, γ-HCH is transformed to extremely low amounts of 1,2,4-trichlorobenzene (1,2,4-TCB) and 2,5-dichlorophenol (2,5-DCP) by S. indicum B90A, but most of γ-HCH were transformed to 2,5-Dichloro-2,5-cyclohexadiene-1,4-diol (2,5-DDOL) by S. japonicum UT26. These results revealed that haloalkane dehalogenases in some Sphingobium species are very active at temperature as low as 4 °C and S. indicum B90A might be a good candidate for developing novel bioremediation techniques for cold regions to decontaminate γ-HCH from soils/waters.