Primary Researches On The Optimization Of The Ferment Condition Of A Endophyte Strain With Antibacterial Activities In Oxya Chinensis

Serratia marcescens, which belongs to the Enterobacteriaceae, is a kind of Gram-negative bacteria, and normally live in soil, water, plant, as well as the intestinal tract and respiratory tract of human being and animals. The researches revealed that their metabolite had very good pesticidal and anticancer activity, which made Serratia marcescens a novel kind of biological resources that had the potential for exploitation and prospect for application. This research used a bacterial strain SDLH-â…¡isolated from the foregut of locust as the material, the zymolytic condition and the characteristic of zymolytic product were studied respectively, and the main results were summarized as follows:Based on the analysis of 15 different physiological-biochemica characteristics, such as different usage of amino acid, the glucide fermentation, decarboxylase reaction, as well as the result of morphologic observation, this bacterial strain SDLH-â…¡was preliminarily identified as Serratia. The full length sequence of 16S rDNA was analyzed by means of PCR, the obtained sequence was used for the homologous sequence searching in Genbank by Blast, then the homology research to other bacterial strains in Serratia was performed. This isolated bacterial strain was finally identified as Serratia marcescens.The passage stability of SDLH-â…¡and their antibacterial spectrum of zymolytic products were analyzed and the results indicated that SDLH-â…¡had stable and high-productive antibacterial effects. The zymolytic products had strong inhibitive effects to indicative strain such as Staphylococcus aureus, and Bacillus subtilis and had inhibitive effects to Gram-negative bacteria such as Escherichia coli and Saccharomyces cerevisia.The experiment by orthogonal design design was used for exploring the optimization of carbon source, nitrogen source level of fermentation medium, the best fermentation medium was determined(α- lactose 2.00 g, tryptone 12.00 g, yeast cream 5.00 g, NaCl 3.50g, K₂HPO₄ 3.68g, KH₂PO₄ 1.32g, distilled water 1000 mL by using distilled water, pH=6.8 )The influence of different element such as cultural temperature, initial pH, inoculum concentration, and fluid volume, age of the strain and the rotate speed of table concentrator to the antibacterial active material was analyzed. The best fermentation condition was determined, it was at 30℃, 10 % of inoculum concentration, pH=6.8, 24h of age of the strain and 150 r/min .The results from the analysis of thermal stability, acidbase stability, light stability, and stability in room temperature indicated that antibacterial activity of fermented products of the bacterial strain SDLH-â…¡could be preserved at room temperature, but was lost at high temperature (80℃) . It suggested that the fermented product could be preserved for long time in the environment that keeps out of the light, has neutral pH and at lower temperature.