Pyruvate formation and sugar metabolism in an amino acid-producing bacterium, Brevibacterium flavum.

Abstract

A Brevibacterium flavum mutant lacking pyruvate kinase, No. 70, grew on glucose, fructose and sucrose as well as the original wild strain did, but was unable to grow on ribose or gluconate unless pyruvate was added. Mutants that required pyruvate for growth on ribose were derived directly from the wild strain. Many of them were completely or partially defective in pyruvate kinase activity. These pyruvate kinase mutants were also unable to grow on gluconate. A phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS) was found in B. flavum, which catalyzed the formation of pyruvate and sugar phosphate from PEP and sugar. The system required Mg2+, acted on glucose, fructose, mannose, glucosamine and 2-deoxyglucose, and existed in the cells grown on any of the carbon sources tested. Cells grown on fructose, mannitol and sucrose, however, exhibited higher PTS activities on fructose than those grown on others. Glucose PTS activity was about 20-fold stronger than that of glucokinase. Other sugar metabolic enzymes, inducible mannitol dehydrogenase, gluconokinase, ribokinase and maltase, as well as constitutive invertase were also detected. Oxaloacetate decarboxylase and malic enzyme, which also catalyzed the pyruvate formation, were found in B. flavum, but the latter activity was very low in cells grown on glucose. The levels of these enzymes in pyruvate kinase mutants unable to grow on ribose or gluconate derived from the wild strain were almost identical to those in the wild-type strain.