Fig. 3

Effects of buffering on 2,3-butanediol production with Bacillus licheniformis DSM 8785. Cultivations on Nakashimada medium with (+) and without (−) addition of 100 mM MES buffer are compared. Variation of the filling volume results in different maximum oxygen transfer capacities in shake flask cultivations. As indicated by the vertical dotted line, the shaking frequency was reduced from 350 to 100 rpm after 3 h. Thereby, oxygen-limited conditions are induced at the same time for all cultivations. Data on oxygen transfer rate (OTR) (a), respiratory quotient (RQ) (b) total 2,3-butanediol concentration (c) and pH (d) are depicted. 2,3-Butanediol is shown as sum of the stereoisomers. The RQ is only shown for OTR > 1 mmol/L/h. To account for the increase of metabolite concentrations due to evaporation of water, all concentrations were corrected accordingly and referred to the initial filling volume. Cultivation conditions: 250 mL unbaffled shake flasks, temperature: 37 °C, shaking frequency: 350/100 rpm, shaking diameter: 50 mm