SUMMARY: Mutants of requiring dicarboxylic acids for an immediate growth response ( and ) oxidize acetate, and are inhibited by fluoroacetate with consequent citric acid accumulation to approximately the same extent as the wild-type. The concentration of nitrogen (as ammonium and nitrate salts) present in the conventional growth medium is inhibitory to the growth of these mutants and leads to an accumulation of acetylmethylcarbinol, pyruvic acid and α-ketoisovaleric acid. This inhibition is reduced and growth is stimulated by the addition of dicarboxylic acids or by diminution of the nitrogen present in ‘minimal’ medium. The addition of nitrogen salts to mutants probably diverts dicarboxylic acids (already in short supply) from the catalysis of the oxidation of C fragments via the tricarboxylic acid cycle to other reactions. This effect of nitrogen salts upsets the already precarious dicarboxylic acid balance of the mutants leading to a growth requirement and to the accumulation of intermediates.


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