Isolation of hexachlorocyclohexane-degrading Sphingomonas sp by dehalogenase assay and characterization of genes involved in γ-HCH degradation

Aim: To screen and identify bacteria from contaminated soil samples which can degrade hexachlorocyclohexane (HCH)-isomers based on dechlorinase enzyme activity and characterize genes and metabolites. Methods and Results: Dechlorinase activity assays were used to screen bacteria from contaminated soil samples for HCH-degrading activity. A bacterium able to grow on alpha-, beta-, gamma- and delta-HCH as the sole carbon and energy source was identified. This bacterium was a novel species belonging to the Sphingomonas and harbour linABCDE genes similar to those found in other HCH degraders. gamma-Pentachlorocyclohexene 1,2,4-trichlorobenzene and chlorohydroquinone were identified as metabolites. Conclusions: The study demonstrates that HCH-degrading bacteria can be identified from large environmental sample-based dehalogenase enzyme assay. This kind of screening is more advantageous compared to selective enrichment as it is specific and rapid and can be performed in a high-throughput manner to screen bacteria for chlorinated compounds. Significance and Impact of the Study: The chlorinated pesticide HCH is a persistent and toxic environmental pollutant which needs to be remediated. Isolation of diverse bacterial species capable of degrading all the isomers of HCH will help in large-scale bioremediation in various parts of the world.