Isolation, Degradation Properties And Pathway Of Degrading Bacteria Dinitroaniline Herbicides Pendimethalin

Pendimethalin(N-(1-ethylpropyl)-2,6-dinitro-3,4-dimethyl aniline; CAS no.40487-42-1) is a dinitroaniline herbicides. Its mechanism of action is inhibiting plant cell division and elongation by entering plant tissues to bind with tubulin. It has been widely used in weeding corn、 potato、rice、 soybean、tobacco、 vegetables and other crops of late years. The excessive use endangers ecosystems and human health on account of pervasive detection in soil、 groundwater、surface water and air. Our laboratory screened two pendimethalin degrading bacteria from inshore sediment of South China Sea and named them WL-4 and WL-6. Based on analysis of morphology、 physio-biochemical characteristics 、 and 16 S r DNA sequence analysis, WL-4 was identified as Pseudomonas sp.WL-4 and WL-6 was identified as Bacillus sp.WL-6. The optimum p H and temperature of Pseudomonas sp.WL-4 and Bacillus sp.WL-6 are 6,7 and 30℃, 35℃ respectively. Andrews equation is used to describe the degradation rate at different initial concentrations. Degradation rate parameters qmax, Ks and Ki were fitted to be 0.02873h-1, 5.629 mg/L, 240.2 mg/L, respectively.During the degradation process of Pendimethalin by Bacillus sp.WL-6, the following 9 metabolites were captured and identified by gas chromatography/mass spectrometry(GC-MS) analysis. The strain was able to degrade Pendimethalin by hydroxylation to form 2-((3,4-dimethyl-2,6-dinitrophenyl) amino)-1-butanol and by dealkylation forming 1-(5-methyl-7-nitro-1H- benzo [d] imidazol-1-yl) propan-1-one. The side chain of Pendimethalin formed hydroxyl by monooxygenase, and then generated 7-amino-5-methyl-1-(pent-3-yl) l H-benzo [d] imidazole-6-carbaldehyde with the action of dehydrogenase. Based on these metabolites, a novel microbial biodegradation pathway of Pendimethalin by Bacillus sp.WL-6 is proposed. Two products of Pseudomonas sp.WL-4 were captured and identified as 1-(5-methyl-7-nitroso-1H-benzo[d]imidazol-1-yl)propan-1-one and 7-amino-5-methyl-1-(pentan-3-yl)-1H-benzo[d]imidazole-6-carbaldehyde. Therefore, this research provides potentially useful information for the application of the Bacillus sp.WL-6 and Pseudomonas sp.WL-4 in bioremediation of Pendimethalin-contaminated water and soil.