Uni- and Dicarbon Metabolism of Methanosarcina Barkeri Strain Ms in Defined Medium
The contributions of C-2 and C-1 labelled acetate to CH4 and CO2 were examined in acetate adapted culture of Methanosarcina barkeri grown in mineral medium. The methyl group of acetate accounted for the majority of CH4 produced; however, 15% of the C-2 of acetate was oxidized to 14CO2. This oxidation correlated with the concurrent reduction of the carboxyl group. 14CH4 was produced from 14C-1 acetate in amounts slightly less than the values detected for 14C-2 acetate conversion to CO2. Acetate adapted cells were capable of simultaneous metabolism of both methanol and acetate during growth in a medium that contained 50 mM of each substrate. The rate of 14CH4 generation from 14C-2 acetate was logrithmic and faster than that observed during unitrophic growth on acetate. The rate of 14CO2 production from 14C-2 acetate was twice that of unitrophic cultures. After methanol depletion the rate of 14CH4 production remained unchanged, while 14CO2 production decreased two-fold. In mixotrophic growth studies with 120 mM methanol and 50 mM acetate the rate of 14CH2 production from 14C-2 acetate decreased several fold over that observed in unitrophic or in the equal (substrate) mixotrophic cultures. However, μ CH4 decreased 2-fold which suggests that methanol toxcity was the cause of this effect.