Sulfate-Dependent Anaerobic Degradation of Herbicide Acetochlor by a Sulfate-Reducing Bacterium Cupidesulfovibrio sp. SRB-5

Acetochlor, an important chloroacetamide herbicide (CAAH) widely used in agriculture, has resulted in environmental contamination, especially of anoxic habitats. In this study, a sulfate-reducing bacterium, designated as SRB-5, was isolated from anaerobic activated sludge and was identified as Cupidesulfovibrio sp. This bacterium possesses a novel anaerobic pathway capable of degrading acetochlor. In this pathway, sulfate is first reduced to sulfide, which attacks the C-Cl bond of acetochlor and abiotically forms acetochlor-thioalcohol and dis-S-acetochlor. These further undergo microbial degradation, producing the intermediates acetochlor ethanesulfonic acid, 2-methyl-6-ethylaniline, and 2-ethylaniline. The degradation half-times of acetochlor (100 μM) by strain SRB-5 were 2.4 and 4.2 days in industrial wastewater and paddy sludge, respectively. Strain SRB-5 could also degrade alachlor, propisochlor, butachlor, pretilachlor, and metolachlor, and the degradation kinetics fit the pseudo-first-order kinetics equation. This work highlights the potential application of strain SRB-5 for the remediation of CAAHs-contaminated sites.