Fig. 5

Influence of different maximum oxygen transfer capacities on 2,3-butanediol production with Bacillus licheniformis DSM 8785. 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) glucose (c), cell dry weight (d), specific oxygen uptake rate (e), total 2,3-butanediol (f), 2,3-butanediol stereo isomer (g and h), glycerol (i) and acetoin (j) concentrations are depicted. In addition to offline samples (half-closed symbols), the concentrations upon glucose depletion were calculated as described in Fig. 4 (closed symbols). For clarity, the connection between the measured and calculated values is shown as dotted line. 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, Nakashimada medium with 100 mM MES buffer