High yield and cost‐effective production of poly(γ‐glutamic acid) with Bacillus subtilis

Poly(γ-glutamic acid) (γ-PGA) is a promising biopolymer with many potential industrial and pharmaceutical applications. To reduce the production costs, the effects of yeast extract and L-glutamate in the substrate for γ-PGA production were investigated systematically at shake flask scale. The results showed that lower concentrations of yeast extract (40 g/L) and L-glutamate (30 g/L) were beneficial for the cost-effective production of γ-PGA in the formulated medium. By maintaining the glucose concentration in the range of 3–10 g/L via a fed-batch strategy in a 10-L fermentor, the production of γ-PGA was greatly improved with the highest γ-PGA concentration of 101.1 g/L, a productivity of 2.19 g/L·h and a yield of 0.57 g/g total substrate, which is about 1.4- to 3.2-fold higher than those in the batch fermentation. Finally, this high-density fermentation process was successfully scaled up in a 100-L fermentor. The present work provides a powerful approach to produce this biopolymer as a bulk chemical in large scale.