Nutrition and carbon metabolism of Methanococcus voltae

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Abstract
M. voltae is a heterotrophic, H2-oxidizing methanogenic bacterium. In complex medium, this bacterium has a doubling time of 1.2 h at its temperature optimum of 38.degree. C. In defined medium, optimal growth is obtained with 0.75 mM isoleucine, 0.75 mM leucine, 2.5 mM acetate, 5 mM NH4Cl, 84 mM MgSO4, 0.4 M NaCl, 1 mM CaCl2, 10 .mu.M Fe2O3 and 0.2 .mu.M NiCl2. In addition, pantothenate, sodium selenate and Co stimulate growth. Optimal growth is obtained between pH 6.0 and 7.0 with either H2 or formate as the electron donor. The volatile fatty acids 2-methylbutyrate and isovalerate can substitute for isoleucine and leucine, respectively. Cellular C is derived from acetate (31%), isoleucine (22%), leucine (25%) and CO2 (23%). The amino acids and fatty acids are incorporated almost exclusively into protein. A comparison of the incorporation of U-14C-amino acids and 1-14C-fatty acids indicated that the fatty acids are degraded during incorporation into cell protein. The distribution of C from the amino acids suggests that acetyl CoA is not a major intermediate in the degradation of these compounds. Thus, M. voltae may convert isoleucine and leucine to other amino acids by a unique mechanism. The lipid C is derived largely from acetate. Thus, the isoprenoid lipids are synthesized de novo from acetate rather than by degradation of leucine. The C in the nucleic acids is derived from CO2 (45%), the C-1 of acetate (25%), the C-2 of acetate (22%), and isoleucine and leucine (7%). This labeling pattern is consistent with known biochemical pathways.