The large scale fermentation of γ-polyglutamic acid (γ-PGA) by Bacillus subtilis (natto) was done using a 30-liter jar fermenter. A stable cultivation without foaming could be done with addition of 3% NaCl to the medium. The γ-PGA productivity became higher with increasing speed of agitation and amounts of glutamic acid added to the broth. Finally, we were able to obtain about 35 mg/ml of γ-PGA under the optimum conditions. The glutamic acid added to the medium was efficiently converted into γ-PGA in the stationary phase. To discover the role of l-glutamic acid added to the medium for γ-PGA biosynthesis by Bacillus subtilis (natto), the radioactivity incorporated into γ-PGA from (14)C-l-glutamic acid was measured. As a result, radioactive γ-PGA was detected in the medium. Then, the glutamic acid in the medium was transported into the cells and actually polymerized as the glutamic acid unit of γ-PGA.
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Ogawa et al. (1997) studied this question.