Phosphoenolpyruvate: Sugar Phosphotransferase Systems and Sugar Metabolism in Brevibacterium flavum

Brevibacterium flavum mutants defective in the phosphoenolpyruvate (PEP)-dependent glucose phosphotransferase system (PTS) were selected with high frequency by 2-deoxyglucose-resistance. Most of them (DOG^r) still had the fructose-PTS and grew not only on fructose but also on glucose like the wild-type strain. A mutant having 1 /8th the fructose-PTS activity of the wild strain but normal glucose-PTS activity was isolated as a xylitol-resistant mutant. It grew on glucose but not on fructose. The glucose-PTS was active on glucose, glucosamine, 2-deoxyglucose and mannose, and slightly on methyl-a-glucoside and N-acetylglucosamine, but not on fructose or xylitol. The fructose-PTS acted on fructose and xylitol, and to some extent on glucose but not on glucosamine or 2-deoxyglucose. Mutants unable to grow on glucose (DOG^rGlc^-) derived from a DOG^r mutant were all defective in the fructose-PTS. All revertants able to grow on glucose derived from a DOG^rGlc“ mutant had the fructose-PTS. The glucokinase activity was about 2/3rds the glucose activity of the fructose-PTS. All the DOG^rGlc^- mutants had normal levels of glucokinase. One of these mutants grew on maltose and sucrose, which were hydrolyzed to glucose. Thus, glucokinase seems to contribute to the phosphorylation of glucose liberated inside the cell. The fructose-PTS was induced by fructose and repressed by glucose. The glucose repression was not observed in a mutant defective in the glucose-PTS.