Study On Mutation Breeding And Solid Fermentation Of Antagonistic Organisms Against Pseudomonas Solanacarum

Ginger bacterial wilt is a destructive disease caused by Pseudomonas solanacarum Smith. The prevention against the disease was always through agricultural and chemical measures since long ago. At present, all kinds of chemical pesticides are employed in the prevention. However, such method is of little effect and is hard to eradication it fundamentally. The application of chemical pesticides lead to the increase of noxious and harmful materials in rhizome, as a result, the products is hard to bring into the international market. During the past a few years, ginger bacterial wilt presents on a widespread and serious tendency as a result of the large amount use of chemical fertilizer, the increase of soil cropping index, and lack of an idea method for prevention and cure. Biological control by natural antagonistic organisms is a potential methord against plant diseases for its innocuity and side-effect free. The strain SR-11 was isolated from the soil collected from some counties of Sichuan province. By identification, the strain was regarded as Streptomyces, which showed good antagonism against pathogenic fungus and bacteria. So in our test, the studies on mutation breeding of strain SR-11 and solid fermentation of strain SR-9 were carried out.The logarithmic phase of strain SR-11 growing in mycelium culture medium is 50～55h. And mycelium growing in culture medium including 0.5% glycine and 4% saccarcose not only is better to growing but also separating of mycelium as well as the releasing of protoplast. The forming speed of protoplasts showed no statistic difference when using mycelia of initial growth stage, anaphase, and stationary phase. The best lysozyme concentration of strain SR-11 was 2mg/mL when it was water bathed at 32℃for 90min. After treating by UV, strain SR-11 was treated by NTG in a form of gradient plate, a mutant strain, number 9 (9# ), was selected. The bioactivity was enhanced 68.42% when compared with the initial strain. The study on stability of passage showed that the mutant strain was stable after seven generations' selection.The antibiotic components obtained from solid fermentation showed good antibiotic activity against Pseudomonas solanacarum Smith and has inhibitive effect on Escherichia coli, Bacillus subtilis, Staphylococcus aureus and some kinds of pathogenic fungi such as Curuvularia Lunata (Walk) Boed, Rhizoctonia solani, Cochlibolus Heterostrophus, Exserohilum Turcicum, Cochliobolus carbonum, Pestalotiopsis foedans, Altalaria altanata, Fusarium graminearum, etc in the antimicrobial spectrum test. The stability of antibiotic components produced by SR-9 was also studied. The results showed that the antibiotic components were acid-and-alkali-base stable under pH3.0～11.0 and heat-stable treated by 37℃～100℃for 10min, and maintained antibiotic activity after treatment of proteinase K and trypsin for 1h. The studies on the bioactivity of the antibiotic components of Streptomyces SR-9 cultured in different inorganic salts, growth factors, nitrogen sources, carbon sources, fermentation temperature, pH, and time were carried out. The results showed that the optimal carbon source, nitrogen source, metallic salts and growth factor were soybean powder, urea, FeSO₄, and peptone respectively. The maximuml bioactivity of the antibiotic components was achieved when cultured at temperature 28°C and the initial pH of 7.0～7.4. Fermentation time would also influence the yield of antibiotic components on different levels. In addition, the antibacterial bioactivities and antimicrobial spectrum were showed no significant difference between the strain SR-9 cultured in liquid culture medium and in solid culture medium.