Mutants ofEscherichia coli defective in acid fermentation

Wild typeE. coli ferments glucose to a mixture of ethanol and acetic, lactic, formic, and succinic acids. Mutants defective in acid production have now been isolated, including those defective in lactate dehydrogenase (LDH) or with excess alcohol dehydrogenase. These mutations had no phenotype without apfl mutation. Novel mutants affecting acetate metabolism were isolated by insertion of the fusion vector Mudl. TheseaceG mutants cannot grow anaerobically on glucose or aerobically on acetate yet lack the pleiotropic growth defects of previously knownpta/ack mutants. In some genetic backgrounds acetate negative mutations suppress the growth defects ofadh mutations. These results are discussed in terms of redox balance.