[Isolation of quizalofop-p-ethyl-degrading bacteria from soil by DGGE-colony in situ hybridization].

Naturally occurring bacteria isolates capable of metabolizing pesticides have received considerable attention because they offer the possibility of both environmentally friendly and in situ remediation. The effect of herbicide quizalofop-p-ethyl on bacterial community in soil was analyzed using the technique of PCR-DGGE for isolating strains biodegrading quizalofop-p-ethyl. Results indicated that the soil bacterial community structures significantly changed after adding quizalofop-p-ethyl. The bacterial diversity of soil showed an increasing-decreasing-increasing trend. The largest changes occurred in the 9th day and then became stabilized. According to the sequencing results of bands in DGGE profiles, it inferred that members of bacterial genera Pseudomonas, Massilia and Burkholderia had tolerance to quizalofop-p-ethyl, and the potential for degradation. These microbial groups could be used to isolate and screen as the indigenous microbial resources to reduce pesticide residues. Digoxigenin-labeled probes had been synthesized based on the sequencing results of bands in the DGGE profiles, and three bacterial strains capable of biodegrading quizalofop-p-ethyl were isolated from soil by colony in situ hybridization technique. The strain named L1 was able to utilize quizalofop-p-ethyl as the sole source of carbon. The strain was identified as Pseudomonas sp., based on the phylogenetic analysis of 16S rRNA. The degrading ability of strain L1 in minimal medium with quizalofop-p-ethyl was investigated by HPLC. The quizalofop-p-ethyl content decreased by almost 50% after 7 days, and the biomass of strain L1 increased while the content of quizalofop-p-ethyl was decreased. This confirmed that the strain L1 had the capacity of degradation. This result provided a basis for future research on degradation mechanism and functional genes.