| Total 27 predominant bacterial isolates were collected and isolated from various plant leaves. The SOD activities in these isolates were detected by photochemical method after the peparation of cell extracts, and it was found that the SOD activities varied in different isolates, the bacterial strain 276, which isolated from rice leaves, showed the highest activity of SOD among these bacterial isolates. The detection of SOD activity in native polyacrylamide gel Electrophoresis (PAGE) electrophoresis also showed the difference in SOD activities among various bacterial strains and the bacterial strain 276 had the highest activity of SOD, which was consistent with the result detected by photochemical method. . Moreover, some samples appeared several active bands in the gel, which indicated the existence of different types of SOD or multi-subunits of SOD in these samples.The bacterial strain 276 is a gram-negative rod bacterium and there are more than 3 polar flagella, which observed after the Gram's staining and flagellum staining. It was identified further as Stenotrophomonas maltophilia and belongs to the aerobic organism according to the results of related biochemical's tests.When the bacterial strain of S. maltophilia 276 was cultured in the three media of LB, PDA and KMB, and the SOD activities of cell extracts were detected, it was found that S. maltophilia 276 could produce higher activity of SOD when cultured in LB media than that in the other two media.The SOD activity in S. maltophilia 276 increased rapidly during the bacteria growth at early log phase, and reached highest with 570 units/ml of cell extract (from 10 ml of cell culture) at the end log phase of bacterial growth. The SOD activity decreased when the bacteria entered growth of stationary phase. It was clear that the production of SOD by S. maltophilia276 was consistent with the growth of bacteria.The cell extract aliquots were added by ammonium sulfate with 30%, 40%, 50%, 60%, 70%, 80% and 90% saturation, separately. The activities of SOD for the re-suspensions were detected after dialysis and centrifugation. It was found SOD activity could be detected after the precipitation by ammonium sulfates with 30% saturation or above, and the highest SOD activity could be obtained by precipitation of ammonium sulfate with 80% saturation.The enzyme was purified from cell extract by ammonium sulfate fractionation (30%-80% saturation) and consecutive column chromatography using DEAE-cellulose and Sephadex G-100. The SOD activity for purified enzyme could reach 4966 IU/mg proteins, and the molecular weight of the SOD was about 20 Kda which determined by SDS-PAGE Electrophoresis.When the non-denaturing polyacrylamide gel stained with substrate for SOD in the present of 0.2mMol/L KCN or 0.5 mMol/L H2O2, the active band was still showed at the same position, which indicated the SOD could not be inhibited by the treatments with KCN or H2O2 and it was the Mn SOD. While, when the aliquots of SOD sample were added with NaCl, KC1, KCN, H2O2 or SDS, respectively, to the final concentration of 0.1mMol/L, 0.5mMol/L and 1.0mMol/L for each chemical, and incubated at 25C for 120 min, the SOD activity, detection by photochemical method, was not influenced by the treatments with 1.0 mMol/L of KCN, H2O2, KC1 or NaCl, but it could be inhibited by the treatments with 1.0 mMol/L of SDS.The SOD had the maximum activity at pH7.8, and the activity of SOD would reduce as the decrease of pH value from 7.8 to 5.0 or as the increase of pH value from 7.8 to 9.0. The SOD it was stable up to 85℃ treatment for two hours, and decrease only 12 % after treated at 90℃ for 30min. The activities of SOD could remain about 85 % after treated at 100℃ for 10min. The activity of SOD could increase as the longer of storage time no matter the samples covered with vegetable oil or not, kept in light or in dark.In the PCR reaction, a DNA fragment with about 550pb length has been amplified by using the genomic DNA of S. maltophilia 276 as the temperate, and by using the sequ...
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