Abstract:
Object Bacteria capable of degrading phoxim were isolated from field soils and identified by 16S rDNA sequencing prior to characterization and evaluation for pollution abatement of the organophosphate insecticide on farmland. Possibility of utilizing the bacterium for disease prevention was also explored.
Method Phoxim-degrading bacteria were isolated on the enrichment culture and identified by 16S rDNA sequences analysis combined with morphological, physiological, and biochemical characteristics. Specific agent in the bacterium responsible for the degradation was located by a plate activity test, and its degrading effect on phoxim-containing wheat bran determined by HPLC. For possible application in disease preventions, the efficacy of the isolated bacteria on fungal phytopathogens was tested with a dual-culture agar plating technique.
Result A phoxim-degrading bacterium designated as D39 was isolated from the soil polluted by the pesticide and primarily identified as Delftia sp. The endoenzyme in D39 was determined to be the key agent responsible of the insecticide degradation. The enzyme was, thus, extracted to spray at a concentration of 0.10 g·kg−1 onto wheat bran spiked with 300 mg·kg−1 of phoxim. As measured by HPLC, the treatment produced a 100% phoxim reduction on the bran after 11 h at 25 ℃. Separately, the antagonism study by the dual-culture plating showed that D39 affected 5 tested phytopathogens in varying degrees. The highest average inhibition rate exerted by D39 was 50.00% on Rhizotonia cerealis, and the lowest 21.05% on Curvularia lunata.
Conclusion D39 could not only efficiently degrade phoxim residues on wheat bran but also inhibit the growth of a certain phytopathogens. It appeared that the extracted endoenzyme from D39 could be applied on grains to decompose the residual insecticide for food safety improvement and served as a disease prevention bioagent as well.
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