Chlorpyrifos bioremediation in Pennisetum rhizosphere by a novel potential degrader Stenotrophomonas maltophilia MHF ENV20

Rhizoremediation is a specific type of phytoremediation involving both plants and their rhizosphere associated microbes. In the present study Pennisetum pedicellatum and rhizosphere associated degrading strains were evaluated for chlorpyrifos remediation. Time-course pot experiments were conducted in greenhouse with P. pedicellatum grown in soil amended with chlorpyrifos at the concentrations of 10, 25, 50, 75 and 100 mg/kg for 60 days. The half life of chlorpyrifos varied from 19.25 to 13.02 days in planted treatments. Residual concentrations of chlorpyrifos were negatively correlated with abundance of degrading microorganisms in rhizosphere. The isolated species of Bacillus, Rhodococcus and Stenotrophomonas were evaluated for their degrading potential in mineral medium. A novel isolated strain of potential degrader Stenotrophomonas maltophilia named as MHF ENV20 showed better survival and degradation at high concentration of chlorpyrifos. Degradation of chlorpyrifos by strain MHF ENV20, 100, 50 and 33.3% degradation within the time period of 48 h (h), 72 and 120 h at 50,100 and 150 mg/kg concentrations, further the gene encoding the organophosphorous hydrolase (mpd) was amplified using PCR amplification strategy and predesigned primers. Our findings indicate that rhizosphere remediation is effective bioremediation technique to remove chlorpyrifos residues from soil. P. pedicellatum itself, in addition to the rhizosphere bacterial consortium, seemed to play an important role in reducing chlorpyrifos level in soil. High chlorpyrifos tolerance and rhizospheric degradation capability of P. pedicellatum, makes this plant suitable for decontamination and remediation of contaminated sites. The ability to survive at higher concentration of chlorpyrifos and enhanced degrading potential due to presence of mpd gene make S. maltophilia MHF ENV20 an ideal candidate for its application in chlorpyrifos remediation.