Enhanced production of antifungal substance (PAFS) biosynthesized by Pseudomonas aeruginosa and examination of its physiological characteristics in fermentation

摘要

Selection of high producer strain, optimization of production medium and cultivation in bioreactor system were carried out in order to produce an antifungal substance, PAFS, in large amounts which was biosynthesized by Pseudomonas aeruginosa as secondary metabolite. By investigating 20 kinds of carbon sources and 41 kinds of nitrogen sources, a synthetic medium consisting of fructose (70 g/l) and ammonium sulfate (10 g/l) and a complex medium including galactose (30 g/l), fructose (20 g/l) and cottonseed flour (35 g/l) were determined as optimized media for PAFS production. In bioreactor studies examining physiological characteristics of the producer microorganism with the complex medium, typical pattern of diauxic growth was observed as demonstrated by the result that fructose was not used before almost exhaustion of readily utilizable carbon source, galactose. When galactose was supplemented additionally during the fermentation period, PAFS productivity did not increase any more, indicating that large portion of the added galactose was used for cell growth instead of biosynthesis of the secondary metabolite. It was deduced that PAFS production could be enhanced by employing fed-batch operation in order to overcome the apparent phenomenon of catabolite repression and/or inhibition.