The incorporation of acetate by the chemoautotroph Thiobacillus neapolitanus strain C |
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Authors: | D P Kelly |
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Institution: | (1) Baas-Becking Geobiological Laboratory, Bureau of Mineral Resources, Canberra, A.C.T., Australia |
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Abstract: | Summary Cultures of Thiobacillus neapolitanus strain C assimilate 14C-labelled acetate and aspartate. Both carbon atoms of acetate are incorporated, and 25% of the cell carbon can arise from acetate. Aspartate-14C contributes 4–5% of the cell carbon, and is found in pyrimidines and in protein as aspartate and its related amino acids. Acetate-14C contributes to lipid, glutamate, arginine, proline and leucine, but not to aspartate. Acetate assimilation by washed organisms requires carbon dioxide and energy from thiosulphate oxidation. Degradation of 14C-glutamic acid from acetate-14C-labelled bacteria; the accumulation of 14C-citrate in the presence of fluoroacetate and 14C] acetate; short-term kinetic experiments on acetate-14C turnover; and the demonstration of citrate synthesis by cell-free extracts all indicate glutamate synthesis from -ketoglutarate formed by reactions of the tricarboxylic acid cycle. The cycle is believed to be incomplete, probably not proceeding further than -ketoglutarate, and functions as a glutamate-synthesising system, using oxaloacetate derived solely from carbon dioxide fixation. Malate synthase (and the glyoxylate cycle) appear to be insignificant in the metabolism, but extracts did form citramalate from acetate and pyruvate. |
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