Proficient Biodegradation Studies of Chlorpyrifos and its Metabolite 3,5,6-Trichloro-2-pyridinol by Bacillus subtilis NJ11 Strain

Abstract

Background and Objective: Chlorpyrifos (CP) is one the most widely used broad spectrum organophosphorus (OP) pesticide in agricultural fields worldwide particularly in Punjab, India. Scarcity of the knowledge in farmers regarding the usage, handling and safety concerns of pesticides leads to massive and uninhibited use of CP. Upon hydrolysis, CP usually generates diethyl thiophosphoric acid (DETP) and 3,5,6-Trichloro-2-pyridinol (TCP), later one possess antimicrobial attributes. Residues of both CP and TCP have been detected in ecosystems and imparts numerous toxicological effects on the various life forms particularly in humans. Hence, their elimination from the contaminated environmental sites is highly needful and bioremediation is the most convenient option at present as it is cost-effective and ecofriendly. Thus objective of the present study was to isolate a bacterial strain having the capability to degrade CP and TCP both completely in to less toxic forms. Materials and Methods: Bacterial strain was isolated from CP and TCP contaminated soils of Malwa region of Punjab where CP has been used continuously in agricultural fields. The CP utilization capabilities of bacterial strain were analyzed by HPLC, HPTLC and other chemical based colorimetric methods. Minimum inhibitory concentration of CP and TCP on the strain was analyzed and also influence of pH and temperature on the growth of isolate was assessed. Results: Strain was found to be Gram positive and was able to use CP as well as TCP as sole carbon source. Molecular characterization based on 16S rRNA gene sequence homology confirmed its identity as Bacillus subtilis. The HPLC studies revealed almost complete degradation of 150 ppm of CP within 5 days without accumulation of TCP in the system. Isolate was competent to tolerate initial CP concentration as high as 800 ppm and present study report firstly of tolerating such higher concentration by Bacillus subtilis strain. Isolate was well adapted to grow within the wide temperature (25-40EC) and pH (6.0-9.0) range. Conclusion: The isolate Bacillus subtilis NJ11 was found to be efficient in the remediation of CP and TCP in liquid medium by converting them into lesser toxic intermediates. Present study suggested that strain has potential to clean up the CP and TCP contaminated sites.