Fig. 1

Extended-batch-cultivation of G. oxydans 621H ΔhsdR pBBR1p264-fdhSCL-ST in a 2 L Visual Safety Fermenter (VSF, Bioengineering) with constant feeding of fructose (1035 g/L) between 19 and 61 h. Depicted is A the oxygen transfer rate (OTR, light blue), carbon dioxide transfer rate (CTR, orange) and respiratory quotient (RQ, dark red), B pH (pink), aeration rate (green) and filling volume (grey), C the dissolved oxygen tension (DOT, dark blue) and agitation rate (light green), D the optical density OD₆₀₀ (purple) and osmolality (black), E fructose (light blue) and 5-ketofructose concentration (red). Cultivation was performed in complex medium with 150 g/L initial fructose at 30 °C, initial pH value 6, pH control at 5.5 from 19–61 h and 5 from 61 h with 3 M KOH, V_L,start = 0.8 L in a 2 L fermenter. DOT was kept ≥ 30% by variation of agitation speed (500–2050 rpm), absolute aeration rate Q_g = 1 SL/min. Feeding solution: 1035 \(\pm\) 10 g_fructose/L, heat pretreatment: 121 °C, 21 min. Feed rate: 14.3 g_fructose/h. Fructose feeding solution and peripheral feeding system were heated to ~ 55 °C. RQ-values are only shown, when OTR-values are above 5 mmol/L/h