2. Materials and methods
2.1. Strain and medium
C. acetobutylicum ATCC 824 (corresponding also to C. acetobutylicum
DSM 792) strain was used in all the fermentations. The
cells were stored on reinforced clostridia medium (RCM) plates at 4 ◦C. The culture was inoculated in 10 ml clostridia growth medium
(CGM) (Wiesenborn et al., 1988) containing 30 g l−1 glucose. The
CGM liquid precultures were gassed with nitrogen to ensure anaerobic
conditions using the Hungate technique and kept at 37 ◦C for
18–20 h to ensure cell growth. The 10 ml liquid preculture was
transferred to a 100 ml serum bottle containing CGM. At least two
culture transfers were made before inoculating the reactor. The
CGM comprised the components below per liter of double distilled
water. Solution I: 5 g yeast extract; 0.75 g KH2PO4; 0.75 g K2HPO4;
1 g NaCl. Solution II: 2 g (NH4)2SO4; 0.2 g MnSO4·H2O; 0.01 g
MnSO4·H2O; 0.01 g FeSO4·7H2O; 0.5 g l-asparagine and 60 g glucose.
Solution I ingredients were autoclaved together at 120 ◦C for
20 min; stock liquids of all solution II and the glucose were prepared
and autoclaved separately and mixed into the final medium according
to the concentrations above. The FeSO4·7H2O and asparagine
were sterile filtered. The final medium had a pH of 6.4–6.5.