Research Of Activity And Mechanism On Pemcillium Digitatum By Antagonistic Bacteria RY3

For a high activity of antagonistic bacterium RY3early screenedfrom the soil,through a combination of determination of morphological,physiological and biochemical characteristics of bacteria,16S rDNAsequencing, the result indicated thebacterium Bacillus as Bacillus amyloliquefaciens. This thesisoptimized the fermentation medium composition and conditions, andstudied its physico-chemical characterization and bacteriostaticmechanism, offering a foundation for biologicalcontrol application of antibacterial substance.We found the the stain of RY3was broad-spectrum antifungalthough confrontation training. It had a great inhibitation on Penicilliumdigitatum,Penicillium expansum, Monilinia fructicola, Diplodia natalensis,Alternaria Nees exWallr., Botrytis cinerea. Expecially, the inhabitation on Penicilliumdigitatum was best.Via single factor and orthogonal experiments, we optimizedthe fermentation medium composition and condition by shake flaskfermentation. The result showed that the optimal culture medium wassoluble starch1%, soybean cake powder0.5%,NH4HCO31%, CaCO30.5%; and the optimal culture conditions wasshaking speed180r/min, inoculum size2%, volume of liquid125ml/250ml, initial pH7～7.5,temperature34℃, and culture time28h. Underoptimal fermentation conditions,antimicrobial substances were extracted from RY3fermentationliquor by acid precipitation, whose inhibition rate on spore germinationof Penicillium digitatum was96.92%.For learning physico-chemical characterization and mechanism of RY3antimicrobial crude extracts, we studed the effect of heattreater, pH value, UV irradiation, organic reagents and protease on itsstability. The result showed thatantimicrobial crude extracts had strong stability to thermal, organicreagents, UV,proteinase; but antimicrobial crude extracts were notalkaline resistance. By videomicroscopy, we found that after antimicrobial crude extractstreatment Penicillium digitatum spore germination time was greatlydelayed, and germ tube enlarged; andmycelium occured ablation, break, increasing branch, distortion,and intracellular substance lectin, and so on. Osmotic potentialexperiments found that extractsdamaged the cell membrane, and made permeabilityincrease,even substantial leakage of intracellular proteins and sugar.