Effects Of Fermentation Temperature On Validalycin Biosynthesis

Validamycin A, produced by fermentation of Streptomyces hygroscopicus, is an important antifungal agro-antibiotic widely used against sheath blight of rice plants in East Asian. However, although temperature is a critical factor to fermentation process, research on the effects of temperature on antibiotic fermentation at gene and enzyme level is limited. Taking validamycin fermentation as an instance, in this work, the effect of temperature on validamycin A bioaynthesis of Streptomyces hygroscopicus 5008 was investigated at different fermentation temperatures respectively, and a shreshold of production was found between 35oC and 37oC. At relatively higher temperature, a much higher validamycin A productivity was obtained together with faster protein synthesis,sugar consumption, and pH viration, while the cells entered the declining phase more rapidly. Samples from log, stationary, and declining phases of fermentation at 30oC, 35oC, 37oC, and 42oC demonstrated that three operons, valABC, valKLMN and valG, for all eight necessary structure genes was damatically promoted when temperature reached the shreshold, expecially valKLMN. Enzyme assays of glucose-6-phosphate dehydrogenase of pentose-phosphate pathway and ValG of validamycin A biosynthesis also demonstrated an enhancement. In this thesis, an attempt of insite research on valG expression by florescent protein was also carried out, but only florescence difference related to morphology was observed. These experiments on fermentation kintics, molecular, and enzyme levels demonstrated that a remarkable promotion of gene transcription, a sufficiency precursor supplying and a high metabolic rate at the early stage of fementation have correlation to the distinct production performance at different fermentation temperatures.