Isolation, Identification & Characterization Of High-performance Acetochlor Degrading Bacteria

In recent years, the chloroacetanilide herbicide acetochlor was detected frequently due to its extensive use in various environmental media. Recent studies show that it is highly toxic to some non-target organisms, such as human, animals, plants and microorganisms in the soil. This study intends to isolate and identify a highly effective acetochlor-degrading bacteria, and then research on mechanisms of acetochlor degradation, at last study its application in soil or water remediation, which are of great theretical significance and application value.Three strains of bacteria were isolated and purified from the activated sludge of a pesticide manufacturer in Hangzhou, which was capable of degrading acetochlor. The bacteria were named by MZ-1, MZ-2 and MZ-3. Only one strain, MZ-3, was used for further investigation, because it had the best performance. Physiological characteristics and analysis of 16 S r DNA gene sequence revealed that MZ-3 belonged to Rhodococcus sp.In this study, the isolate could degrade and utilize acetochlor as the sole source of carbon, nitrogen and energy for growth. The optimal conditions for the degradation and growth of MZ-3 were p H 7.0 and 30 °C. Under these conditions, this strain could completely degrade 200 mg/L of acetochlor within 12 h of incubation. When the p H was between 6.0 and 8.0, more than 90% of the 200 mg/L of acetochlor could be degraded by MZ-3 within 12 h, which shows that strain MZ-3 prefers a weak alkaline environment. However, when the p H was at 5.0 or more than 9.0, acetochlor biodegradation was distinctly inhibited. The optimum temperature for the biodegradation of acetochlor was 20~40 °C, which indicated a wide tolerance range for temperature. Furthermore, this particular strain was also found highly effective in degrading alachlor and butachlor, which indicated that the alkyl chain length had no significant influence the N-dealkylation of the chloroacetamide herbicides. During the biodegradation process, the enantioselectivity of the strain was investigated using a chiral high-performance liquid chromatography(HPLC) system. However, no obvious enantioselectivities were found.During the process, 2-chloro-N-(2-methyl-6-ethylphenyl) acetamide(CMEPA) was detected as one of the intermediates of acetochlor using HPLC and liquid chromatography-mass spectrometry(LC-MS) analyses. We speculated that the acetochlor degradation pathway in strain MZ-3 was a C-dealkylation pathway.