Isolation of hexachlorocyclohexane-degrading Sphingomonas sp. by dehalogenase assay and characterization of genes involved in gamma-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 α‐, β‐, γ‐ and δ‐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. γ‐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.