الفهرس | Only 14 pages are availabe for public view |
Abstract A field survey was conducted in El Sharkia and Port Said to collect soil samples from previously herbicides sprayed soils. Soil samples were investigated on herbicides containing media to isolate bacterial strains capable of degrading herbicides and utilized them as carbon and nitrogen source. About 65 bacterial strains were isolated on clodinafop-propargyl (CF) and tribenuron-methyl (TBM) containing media. Only, two bacterial strains named HT31 and HT44 and identified as Bacillus sp. and Bacillus cereus, respectively, utilize clodinafoppropargyl as a carbon source and nitrogen source and degraded 88.7% and 87.5%, respectively, of 80 mg/L CF within 12 h. With the degradation process the bacterial biomass and the chloride ion were increased with the time. The bacterial strain HT31 was higher than the strain HT44 in growth biomass and also in release of chloride ion as a result to clodinafop-propargyl biodegradation. In the same time four bacterial strains were named HT9, HT12, HT16 and HT25 identified, respectively, as Acinetobacter lwoffii, Bacillus thuringiensis, Lysinibacillus sp. and Bacillus sp. Those bacterial isolates utilize tribenuron-methyl when grown on glucose mineral salt medium and degraded 87.8, 85.4, 81.4 and 79.2%, respectively, of initial 50 mg/L TBM within 12 h. The degradation of clodinafop-propargyl and tribenuron-methyl was investigated by HPLC. Whereas, the clodinafop propargyl did not appear in HPLC chromatogram of inoculated media as compared to control (uninoculated media), while the metabolite of clodinafop propargyl appear. The growth of bacterial strain increased with time and the concentrations of herbicides clodinafop-propargyl and tribenuron-methyl decreased. In the same time, the derivatives of herbicides increased with the time. The growth conditions for bacterial isolates indicated that the degradation of herbicides depend on initial herbicide concentration and increasing the herbicide concentration decreased the degradation process. The results indicated that glucose, glycerol and sucrose were the best carbon source for TBM degradation and also NH4Cl was the best nitrogen source for the degradation of TBM. from the results the optimum temperature for the growth of selected isolates to degrade CF and TBM, were between 30 and 35ºC for all strains. Also, the optimum pH for all strains to degrade CF or TBM were between 7 and 8. The selected strains in this study exhibited esterase activities after 12 and 24 hours of incubation in media supplemented with 80 mg/L CF or 50 mg/L TBM. However the esterase activities at 24 hr were less than at 12 hr and this decrease was insignificant with all bacterial strains. The results of this study indicated that those isolated bacterial strains will be subjected to further studies to be used in bioremediation of herbicides residues in contaminated soils to overcome the pollution problem. |