Summary: The percentage of bacterial carbon that was derived from exogenous labelled compounds present in the medium during the growth of some methylotrophs on trimethylamine or on non-C compounds was determined. Less than 10% of bacterial carbon was derived from acetate during the growth of the obligate methylotrophs 4B6 and C2A1, and of the restricted facultative methylotroph PM6; the other restricted facultative methylotroph W3A1 gave a value of 18%. Corresponding values for three typical facultative methylotrophs growing on trimethylamine were 41. 42 and 52%. Aspartate, fructose, pyruvate and succinate made only a small percentage contribution (0.4 to 12%) to bacterial carbon in 4B6, C2AI, W3AI and PM6. Washed suspensions of 4B6, C2AI, W3AI and PM6, all grown on trimethylamine, assimilated labelled acetate only in the presence of trimethylamine and there was a linear relationship between the amount of acetate assimilated and the amount of trimethylamine oxidized. Organisms 4B6, C2AI, W3AI and PM6 assimilated C from labelled acetate predominantly into lipid (except PM6), glutamate, arginine, proline and leucine, whereas the typical facultative methylotrophs assimilated C from acetate into lipid, nucleic acid and all the protein amino acids. These results are consistent with the presence of a deficient tricarboxylic acid cycle in the obligate methylotrophs and in the restricted facultative methylotrophs.


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