SELECTION OF MUTANTS CONSTITUTIVE FOR SEVERAL GLYOXYLATE CONDENSING ENZYMES DURING GROWTH ON VALERIC ACID

An investigation was undertaken to assess the formation of several glyoxylate condensing enzymes during growth on a series of short-chain fatty acids. When Escherichia coli was grown on acetate, high malate synthase and low B-n-propylmalate synthase activities were observed. Cells grown on either propionate or butyrate possessed high malate synthase activity, and in addition formed low levels of [alpha]-hydroxyglutarate, [beta]-ethylmalate and [beta]-n-propylmalate synthase activity. In contrast, growth on valerate effected high activity of all these glyoxylate condensing enzymes. Evidence is presented that valerate does not act to induce or derepress enzyme formation, but rather acts to select a mutant population which is constitutive for the formation of these enzymes. Such mutants also are able to grow with a much shorter lag on propionate, butyrate, valerate, caproate and heptanoate. The possible relationship between formation of these enzymes and growth on short-chain fatty acids is discussed.