Production of poly-γ-glutamic acid by glutamic acid-independent Bacillus licheniformis TISTR 1010 using different feeding strategies

Bacillus licheniformis TISTR 1010 was identified as a glutamic acid-independent producer of poly-γ-glutamic acid (γ-PGA) in a newly modified B medium in a shake flask culture. The fed-batch production of γ-PGA by this strain was optimized through simultaneously and continuously feeding glucose and NH4Cl with manual and pH-stat based feeding methods in a 7-L stirred fermenter. Using the optimized operation, the dissolved oxygen concentration, the pH, the glucose concentration and NH4Cl concentration could be stably controlled to extend the γ-PGA production phase and eliminate the hydrolysis of γ-PGA. As a result, the γ-PGA concentration and productivity reached levels of 27.5 ± 0.2 g L−1 and 0.286 ± 0.059 g L−1 h−1, respectively. These values of final concentration and productivity were 5-fold and 3-fold of those obtained without the optimization.