Factors Affecting Biodegradation of the Organophosphorus Insecticide Diazinon by Bacterial Mono-Culture of Bacillus Sefensis 7, Isolated From the Rhizosphere of Date Palm Tree

Abstract

Due to widespread use pesticides for crop protection, they are considered as contaminants in the, environmental matrices such soil which are exposed to large quantities. Three isolates from soil samples using enrichment culture technique have been isolated and grown in the minimal growth medium where Diazinon served as a sole carbon source (60 mg/l). Total three bacterial strains were screened for Diazinon degradation. The most active one was isolate BMNF7 (33% degradation. Lower degradation percentages were recorded for the two other isolates, BMRF3 and BMTF 8 (21-30%). The isolate BMNF7 was identified by morphological and biochemical studies as Bacillus sp. and identification was confirmed using 16srRNA. It was identified as Bacillus sefensis 7 and this isolate was able to degrade up to 63% of Diazinon (60 mg/l) in mineral salt medium (MSM) as a sole carbon source within 10 days of incubation. The bacterial growth and Diazinon degradation were accelerated when MSM supplemented with 0.75 (g/l) yeast extract and 0.5 g/l glucose as an additional carbon and nitrogen sources. The maximum degradation was obtained at pH 7 and 45oC after 10 days of incubation and using 4x10 6 CFU/ml as inoculum size. It was noticed that the best growth temperature was 37oC while the maximum degradation was at 45oC, meaning that high temperature increased degradation process. In conclusion the bacterial strains isolated from the agricultural soil, especially Bacillus species showed the ability to degrade Diazinon insecticide and optimization of growth conditions enhanced the percentage of degradation.