Isolation & Characterization Of A Cetochlor Degrading Strain Y3B-1 And Its Degrading Characteristics

Acetochlor (2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)-acetamide) is a selective preemergent chloroacetamid herbicide used to control broadleaf weeds and graminaceous annual grasses in several crops such as soya, corn, potato, cotton earthnut in north. It is one of three kinds of herbicides that are the most widely used in China. Although it provides help for agriculture, negative effect should not be ignored. Besides direct toxicity, it is with the characteristict of residue and is difficult for ivolatilization and photolysis. So it is also defined as environment pollute and the potential ecological safety problems would arise after large amount application for a long time.In general, chloroacetamide herbicide's residues and metabolites are relatively common in watershed and groundwater aquifers in agricultural areas that have a history of herbicide application. The prevalence of these compounds in the environment has stimulated investigations into the degradation of hazardous substances in water and contaminated soil. The biological decontamination of pesticide wastes or spills has become an increasingly important area of research. Various studies such as photochemical, microbial and degradative dissipation of acetochlor and its analogous compounds like alachlor. butachlor, pretilachlor and metolachlor were previously reported. However, to date, few pure bacterial cultures that could degrade acetochlor have been described.A acetochlor-degrading bacterium strain, designated as Y3B-1, was isolated from activated sludge of a wastewater treatment facility. This bacterium was preliminarily identified as Paracoccus sp. according to its physiological & biochemical characteristic and the similarity analysis of its 16S rRNA sequence.The investigation of the biological characteristics of strain Y3B-1 showed that the optimal temperature was 30℃. The optimal pH value for the growth of strain Y3B-1 was 7.0. The aeration was related positively to strain growth. The strain Y3B-1 can grew in the condition of 0～20 g·L-1NaCl concentration and grew better in the LB medium with 10 g·L-1 NaCl concentration. The optimal medium for the growth of strain Y3B-1 was glucose as carbon source and organic nitrogen as nitrogen source.Y3B-1 has resistance to ampicilin, cephalosporin and streptomycin.Strain Y3B-1 could utilize acetochlor as sole carbon resource for growth. Strain Y3B-1 was able to degrade 85% of 100 mg·L-1 acetochlor within 3 d. The optimal temperature and pH for the degradation were 30℃and 7.0, respectively. The degradation efficiency was related positively to initial inoculum size while a negative correlation with the initial concentration of acetochlor. When the initial inoculum size was 5%, the degradation efficiency was best. The strain could degrade acetochlor rapidly when initial concentration was 50 mg·L-1, while the degradation rate was significantly reduced when initial concentration was more than 150 mg·L-1. Additional nutrients significantly promoted the degradation efficiencies. Acetochlor was degraded faster than butachlor and pretilachlor, more than 85% of acetochlor and about 65-69% of butachlor and pretilachlor were degraded within 3 days by strain Y3B-1.