Biosynthetic pathways in Methanospirillum hungatei as determined by 13C nuclear magnetic resonance

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Abstract
The main metabolic pathways in M. hungatei GP1 were followed by 13C NMR, with 13C-labeled acetate and CO2 as C sources. The labeling patterns found in carbohydrates, amino acids, lipids and nucleosides are consistent with pyruvate formation from acetate and CO2 as the 1st step in biosynthesis. Carbohydrates are formed by the glucogenic pathway, and no scrambling of label was observed, indicating that the oxidative or reductive pentose phosphate pathways do not function at significant rates. The pathways for amino acid biosynthesis are the usual ones, with the exception of that for isoleucine. The tricarboxylic acid pathway is incomplete and operates in reductive direction to form .alpha.-ketoglutarate. The phytanyl chains of lipids are synthesized from acetate via mevalonic acid.