Addition of Exogenous Oxygen Carrier and Precursor L-Glutamic Acid Enhanced the Production of γ-Poly Glutamic Acid by Fermentation of Bacillus subtilis HB-1

Abstract:

In order to improve the ability of exogenous L-glutamate-dependent strain Bacillus subtilis HB-1 to produce γ-poly glutamic acid (γ-PGA), the study explored the effects of adding oxygen carrier and precursor L-glutamic acid on the cell growth and the yield of γ-PGA. Based on single factor tests, the optimum oxygen carrier was polydimethoxysilane (PDMS), and the cell density increased 3～5 times after the addition of 10% PDMS (v/v) in the initial fermentation medium; moreover, the optimum addition time of precursor L-glutamic acid was 18 h, and the optimum concentration was 10 g/L. With the optimal conditions, the concentration of γ-PGA increased to 45 g/L in a 3 L fermenter, and its yield reached 52 g/L by the combination of feeding carbon source and L-glutamic acid in 30 h. The fermentation product was confirmed to be a polypeptide compound by infrared and amino acid analyzers, and the molecular weight of γ-PGA was up to 10 million dalton.