Identification of a Pb-Resistant Acetochlor-Degrading Bacterium for Bioremediation of Soils Contaminated with Herbicides

Acetochlor, a commonly used herbicide, and Pb are two important soil contaminants often found to co-occur. The cytotoxic effects of heavy metals like Pb considerably reduce the efficacy of microbial bioremediation steps undertaken to remove chemical contaminants from soil. This necessitates the identification of heavy metal-tolerant microbial strains that can degrade chemical pollutants. In the present study, a Pb-resistant acetochlor-degrading bacterial strain belonging to the Serratia genus was isolated. We found that Serratia sp. QSxin4 could use acetochlor as the sole carbon source and grow well when incubated in a minimal medium containing 500 mg/L acetochlor and 200 mg/L Pb. QSxin4 could degrade acetochlor from 500 to about 4.5 mg/L within 48 h, with the maximum degradation rate of 12 ± 0.1 mg mL −1 h −1 . GC-MS analysis showed that the bacterial strain could deoxyalkylate acetochlor to produce 2-ethyl-6-methyl-N-methyl-α-chloroacetanilide. Germination studies carried out with Eragrostis pilosa seeds, using soil containing 25 mg/kg acetochlor and 400 mg/kg Pb, revealed that QSxin4 could markedly reduce the toxic effects of acetochlor on seed germination by degrading acetochlor to a less toxic compound. Our findings indicate that QSxin4 can be used for bioremediation of acetochlor-contaminated soil contaminated with high concentrations of Pb.