Fig. 4
Impact of additional citric acid (a-d) or additional trace elements (e-h) on γ-PGA production of B. licheniformis ATCC 9945. a and e Oxygen transfer rates (OTR) of five and six parallel flasks and optical density (OD600). b and f Derived online viscosity, measured offline viscosity, molecular weight, and concentration of γ-PGA. c and g Carbon source concentrations of glycerol, glutamic acid, and citric acid, and phosphate concentration. d and h Overflow metabolite concentrations of acetate, acetoin, and 2,3-butanediol. Initial values: pH = 7.4, 80 g L−1 glycerol, 20 g L−1 glutamic acid, 18 (a-d) or 12 g L−1 (e-h) citric acid, trace elements (only e-h). Cultivation conditions: T = 37 °C, 500 mL shake flasks, filling volume 100 mL, shaking frequency 250 rpm, shaking diameter 50 mm