Studies on the production and separation of poly (γ-glutamic acd)

Abstract

The process for poly (γ-glutamic acid) (γ-PGA) production by Bacillus licheniformis ATCC 9945A was developed from fermentation to separation and purification. The productivity of γ-PGA fermentation can be increased dramatically by the efficient feeding strategy. That is, the glucose was fed to culture medium, which consists of glycerol, citric acid, and glutamic acid, with keeping the glucose concentration in broth 1 - 5 g/L. There was no catabolic repression due to the glucose feeding. The glucose feeding enhanced the consumption of other carbon sources such as glycerol, citric acid, glutamic acid, finally resulted in the high productivity and high concentration of γ-PGA. The glucose feeding also changed the way of γ-PGA production of cell. The γ-PGA was produced only by growth-associated way in medium E, but its production was continued glucose after the cell entered stationary phase when the glucose was supplied to culture medium. The other carbohydrates such as fructose, sucrose, and maltose also showed similar results. But the concentration of carbohydrates in culture broth should be lower than 20 g/L for avoiding the formation of polysaccharides. The productivity and concentration of γ-PGA was finally obtained 57 g/L and 3.1 g/L/h, respectively with fed-batch culture with glucose under 5 L fermentor. For the mass production of γ-PGA, the scale-up of bioreactor was required. The scale-up of γ-PGA fermentation was not easy because of the high culture viscosity, which could lead the incomplete mixing of nutrient and low mass transfer coefficient. The incomplete mixing could cause the formation of the high glucose concentration region in fed-batch culture with glucose. This stimulates the production of by-products such as polysaccharides. Therefore, the efficient mixing was required for the successful scale-up of γ-PGA fermentation process. The mixing in γ-PGA fermentation was governed by the γ-PGA concentration in broth, thus the γ-PGA solution was used as m...