Two Mutations Affecting Utilization of C4-Dicarboxylic Acids by Escherichia coli

SUMMARY: Studies with a mutant of Escherichia coli reported to be deficient in phospho-enolpyruvate carboxykinase activity (AB257suc-) indicate that it possesses two mutations. One affects growth on succinate (S-), and the other primarily affects growth on fumarate and malate and affects growth on succinate to a lesser extent (FM-). Neither of these mutations has a direct effect on carboxykinase activity. Presence of the S- mutation also prevents growth on acetate. It delays growth on other substrates such as lactate, glycerol and malate and it specifically inhibits the oxidation of succinate by mutant suspensions. The only biochemical lesion which could be detected was a deficiency in succinate dehydrogenase and it is thought that the S- locus may be situated in the structural gene for this enzyme. Transduction with phage P1 indicates linkages between S- and gltA and sucA of 97 and 90%, respectively and the gene order S…sucA…gal was established. The FM- mutation was also found in the parental strain AB257. It affects the oxidation of succinate, fumarate and malate by mutant suspensions. The uptake of the dicarboxylic acids is also impaired but no other biochemical lesion could be detected. Genetic studies indicate that the FM- mutation is located near xyl.