Comparative proteomics unravelled the hexachlorocyclohexane (HCH) isomers specific responses in an archetypical HCH degrading bacterium Sphingobium indicum B90A

Hexachlorocyclohexane (HCH) is a persistent organochlorine pesticide that poses threat to different life forms. Sphingobium indicum B90A that belong to sphingomonad is well-known for its ability to degrade HCH isomers (alpha-, beta-, gamma-, delta-), but effects of HCH isomers and adaptive mechanisms of strain B90A under HCH load remain obscure. To investigate the responses of strain B90A to HCH isomers, we followed the proteomics approach as this technique is considered as the powerful tool to study the microbial response to environmental stress. Strain B90A culture was exposed to alpha-, beta-, gamma-, delta-HCH (5 mgL(-1)) and control (without HCH) taken for comparison and changes in whole cell proteome were analyzed. In beta- and delta-HCH-treated cultures growth decreased significantly when compared to control, alpha-, and gamma-HCH-treated cultures. HCH residue analysis corroborated previous observations depicting the complete depletion of alpha- and gamma-HCH, while only 66% beta-HCH and 34% delta-HCH were depleted from culture broth. Comparative proteome analyses showed that beta- and delta-HCH induced utmost systemic changes in strain B90A proteome, wherein stress-alleviating proteins such as histidine kinases, molecular chaperons, DNA binding proteins, ABC transporters, TonB proteins, antioxidant enzymes, and transcriptional regulators were significantly affected. Besides study confirmed constitutive expression of linA, linB, and linC genes that are crucial for the initiation of HCH isomers degradation, while increased abundance of LinM and LinN in presence of beta- and delta-HCH suggested the important role of ABC transporter in depletion of these isomers. These results will help to understand the HCH-induced damages and adaptive strategies of strain B90A under HCH load which remained unravelled to date.

Automated summary

This study investigates the response of Sphingobium indicum B90A strain to HCH isomers using proteomics approach. The results show that beta- and delta-HCH induced significant systemic changes in the proteome of strain B90A, affecting stress-alleviating proteins.