Production of Poly-γ-glutamic acid by Bacillus licheniformis: Synthesis and Characterization

Poly-γ-glutamic acid (γ-PGA), one type of amino acid polymers, consists of D-and L-glutamic acids linked with amide bonding between α-amino and γ-carboxylic acids. Naturally, γ-PGA could be biodegradable polymer and water-solubleapplied in various industries such as food, cosmetics, and pharmaceutical industries. Variation of initial L-glutamic acid concentration affecting on the production of γ-PGA by fermentation of Bacillus licheniformis was studied. The batch fermentation process consists of preparing the inoculum and expanding the culture of B. licheniformis into E medium (pH 6.5) for γ-PGA production. γ-PGA was recovered by using methanol precipitation together with lyophilization. For characterization, the molecular size of γ-PGA products was analyzed by Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE), and that for characterization of γ-PGA with Fourier Transform Infrared Spectroscopy (FT-IR). The results showed that initial concentrations of L-glutamic acid(0, 15 30, 45, 60, 75 g/L) affected on the production of γ-PGA significantly. In addition, the L-glutamic acid of 75 g/L could contribute the best production of 12.64 g/L γ-PGA, which higher than those concentrations of 45 and 60 g/L L-glutamic acid. Therefore, an increase of the L-glutamic acid concentration correlated well with an increased concentration of γ-PGA polymer. The observations gave an alternative for possible process development of the production of γ-PGA. This is directly applicable in industries, as well as enhancing academic progress in bio-polymer field.