Figure 4

Cultivation of E. coli under induced conditions using auto-induction media. Oxygen transfer rate during cultivation of two E. coli BL21 (DE3) variants expressing 3-hydroxybutyryl-CoA dehydrogenase (E. coli HBD) and glucose 1-dehydrogenase (E. coli GDH) in (A-B, D-E) self-made auto-inducing TB+lactose medium with various yeast extracts as listed in Table 1 and (G-H) two different lots of commercial Overnight Express (OnEx) auto-induction medium. The respiration behavior is categorized into two patterns. Pattern I (Merck, Roth_2, and OnEx_2) is characterized by an initial increase in OTR to a plateau of 35 to 60 mmol/L/h and a second increase to 70 mmol/L/h, whereas the highest OTR is reached immediately in pattern II (AppliChem, DSM, Difco, Roth_1, Roth_4, and OnEx_1). Conditions: 250-mL flask, filling volume 10 mL, shaking frequency 350 rpm, shaking diameter 50 mm, and 37°C. (C, F, I) The volumetric enzyme activity of expressed HBD and GDH was measured in triplicates for all cultivations after 14 h.