Fig. 3.

Influence of citrate addition on growth, pH profile, substrate consumption, and product formation of the C. glutamicum wild type carrying either pAN6-citH (green and blue symbols) or the control plasmid pAN6 (black and red symbols). After the first preculture in BHI medium during the day, a second preculture was performed in CGXII minimal medium with 4% (wt/vol) glucose, 25 μg/ml kanamycin, and 100 μM IPTG overnight. The main culture was performed in CGXII minimal medium with 4% (wt/vol) glucose, 25 μg/ml kanamycin, and 1 mM IPTG. After 4 h of cultivation (OD₆₀₀ ∼5), two of the cultures (indicated by the blue and red symbols) were supplemented with 50 mM trisodium citrate and 5 mM CaCl₂ (black arrows), whereas the two other cultures did not receive a supplement (green and black symbols). Samples were taken at the indicated time points and analyzed for OD₆₀₀ (A), pH of the supernatant (B), glucose consumption (C), citrate consumption (D), lactate formation (E), acetate formation (F), 2-oxoglutarate formation (G), and malate formation (H). The data shown are average values and standard deviations from three independent cultivations.