Microbial Synthesis of γ-poly(glutamic acid)

γ-PGA is a water soluble, polyanionic, biodegradable, extracellular polymer produced by the bacterium, B. licheniformis 9945a. The polymer can be biosynthesized from many different carbon sources including starch, glucose, amino acids, glycerol, citric acid and gluten. We have established effects of physiological variables on γ-PGA stereochemistry, molecular weight and product yield using B. licheniformis 9945a (Giannos et al., 1990; 1991; Birrer et al., 1994; Cromwick et al., 1994; Cromwick and Gross, 1995a; 1995b). In addition, analytical methods to determine molecular weight, yield and stereochemical composition have been established in the laboratory. Our laboratory reported large changes in γ-PGA molecular weight, ranging from 100,000 to 2 million g/mole (Mn), by varying culture conditions. In general, γ-PGA molecular weight decreases during the fermentation period due to the presence of depolymerase enzyme(s). Controlled pH experiments show increased polymer formation at pH 6.5 relative to 5.5 and 7.4. The rate and total volumetric production of γ-PGA increased dramatically with higher oxygenation conditions, 250 to 800 rpm and 0.5 to 2.0 liter air/liter, respectively (Birrer et al. 1994). Finally, variation of the media manganese sulfate concentration from 6.15 x 10-4 M to 0 M resulted in γ-PGA % [D]-glutamate compositions of approximately 90% and 50%, respectively (Cromwick et al. 1995a).