Kinetic studies and medium improvement of growth and vitamin B 12 production by Acetobacterium sp. in batch culture

Abstract

Kinetics of inhibition of the growth of Acetobacterium sp. by methanol (substrate) and acetate (inhibitory end-product) were analyzed using a second-order substrate inhibition model coupled with a non-competitive product inhibition model. The analysis revealed that the substrate saturation constant K s was 83.1 mM methanol; the substrate inhibition constant K i was 277.8 mM methanol; the inhibition constant K p was 0.835 mM undissociated acetic acid (239 mM of total acetic acid at pH 7.2); the exponent of inhibition n was 0.72; and μ max was 0.175 h −1. The growth characteristics of Acetobacterium sp. in a defined medium containing methanol and CO 2 were investigated and this medium was modified in order to optimize growth of the bacterium and production of vitamin B 12 in batch culture. The composition of the modified medium was as follows (per liter of deionized water): methanol, 8 g; NaHCO 3, 15.0 g; KH 2PO 4, 0.685 g; NH 4Cl, 1.0 g; MgSO 4·7H 2O, 0.1 g; CoCl 2·6H 2O, 0.02 g; 5,6-dimethylbenzimidazole, 0.02 g; yeast extract, 2.0 g; l-cysteine-HCl·H 2O, 0.5 g; trace element solution, 80 ml; vitamin solution, 40 ml; titanium (III) citrate, 0.015 mM. The maximum cell concentration of Acetobacterium sp. doubled (1.3 g/ l) when the acetogen was grown in the modified medium compared with that in the basal medium (0.63 g/ l).