2.1 Cultures and Media
C. acetobutylicum ATCC55025 was cultured in modified P2 medium
containing (per liter, at pH 5.5): 0.5 g
KH2PO4, 0.5 g
K2HPO4, 1 g yeast extract, 0.5 g
tryptone, 0.2 g MgSO4∙7H2O, 0.01 g
MnSO4∙H2O, 0.01 g NaCl, and 0.01 g
FeSO4∙7H2O, 0.1 mg p -aminobenzoic
acid, 0.1 mg thiamine, 1 µg biotin, and 50 g glucose as the carbon
source, unless otherwise noted (Xu et al., 2015). Concentrated mineral
(MgSO4∙7H2O,
MnSO4∙H2O, NaCl,
FeSO4∙7H2O) and vitamin
(p -aminobenzoic acid, thiamine, biotin) solutions were prepared
separately, filter-sterilized with 0.2 µm pore size filter and stored in
a refrigerator until use. The medium without glucose was sterilized by
autoclaving at 121 ºC for 30 minutes. The main carbon source, glucose,
was sterilized separately in a concentrated solution and added
aseptically to the medium to a final concentration of
~50 g/L or as specified. Butyric acid at various amounts
(up to 10 g/L) was also added to the medium to study its effects on cell
growth and fermentation kinetics. The medium was adjusted to pH 5.5 with
NH4OH and purged with sterile N2 for
~30 min to reach anaerobiosis before use.