Study On Fermentation Production Of γ-PGA By Bacillus Subtilis ZJU-7

Poly-γ-glutamic acid (γ-PGA) is a kind of extracellular anionic polypeptide that is produced by microbe. It is made of D- and L-glutamic acid units linked by amide linkages betweenα-amino andγ-carboxylic acid groups. As a sort of biomaterial,γ-PGA is non-toxic to human and the environment.A strain with highγ-PGA synthesizing ability was screened from Bacillus subtilis ZJU-7 which was preserved in our laboratory with a new strain rejuvenation method. In order to decrease the cost ofγ-PGA production, the experiments of nitrogen source substitution were carried out and a cheap and efficient nitrogen source was screened out.Experiments of batch fermentation were done in 15L fermentor, including investigating the effects of initial glucose concentrations and bran acid (glumatic acid) as precursor. The result showed that high viscosity (4200mPa·s) was attained by using 100g/L glucose in the medium.Fed-batch fermentations were carried out in 10L fermentor by feeding glucose and precursor, and further was scaled up from 10L fermentor to 100L fermentor. When the glucose concentration was maintained over 50g/L by glucose feeding, the viscosity could reach 6000mPa·s, much higher than those under the controlled glucose concentration of 10g/L or 30g/L. andγ-PGA productivity was 59g/L. When the bran acid feeding started at early phase, the productivity of PGA would decrease because too much biomass was brought, but further medium feeding would support a second growth phase and the viscosity could reach 7000mPa·s. Further up-scaled experiment indicated that similar fermentation results could be obtained in 100L fermentor, and theγ-PGA productivity reached up to 54g/L.Further work was done to construct a new type bioreactor (CFBB) to carry out immobilized fermentation. It was found that the strain ZJU-7 could absorp to the surfaces of the towel effectively in CFBB, and the ratio of immobilized cells to free cells was 0.625, and high viscosity (4000mPa·s) was obtained. Further efforts were necessary to optimize the culture conditions for high production ofγ-PGA.