Utilization of Methanol plus Hydrogen by Methanosarcina barkeri for Methanogenesis and Growth

Methanosarcina barkeri grew on methanol plus H₂. Both substrates were consumed in equimolar amounts. Growth was strictly dependent on the presence of acetate, which was required for the biosynthesis of cellular constituents. Only about 0.4% of the methane produced originated from acetate. By using deuterated methanol, it was demonstrated that methanogenesis from this compound under H₂ did not occur via oxidation of methanol to CO₂ and subsequent reduction but by direct reduction with H₂. Growth yields with methanol plus H₂ and with methanol alone were not significantly different: 2.8 g of cells per mol of methanol in mineral medium and 4.6 g of cells per mol of methanol in complex medium, respectively. Growth of M. barkeri on methanol plus H₂ depended strictly on the presence of sodium ions in the medium. In the presence of 50 mM K⁺ the K_s for Na⁺ was 5 mM.