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-alpha -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.

Automated summary

In this study, a Pb-resistant acetochlor-degrading bacterial strain belonging to the Serratia genus was isolated. The strain QSxin4 can efficiently degrade acetochlor and reduce its toxic effects on seed germination in the presence of high concentrations of Pb, showing potential for bioremediation of acetochlor-contaminated soil.