Uni- and Dicarbon Metabolism of Methanosarcina Barkeri Strain Ms in Defined Medium

Abstract

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.