H⁺-ATPase defect in Corynebacterium glutamicum abolishes glutamic acid production with enhancement of glucose consumption rate

Abstract.

A mutant of Corynebacterim glutamicum ('Brevibacterium flavum') ATCC14067 with a reduced H⁺-ATPase activity, F172–8, was obtained as a spontaneous neomycin-resistant mutant. The ATPase activity of strain F172–8 was reduced to about 25% of that of the parental strain. Strain F172–8 was cultured in a glutamic-acid fermentation medium containing 100 g/l of glucose using a jar fermentor. It was found that glucose consumption per cell during the exponential phase was higher by 70% in the mutant than in the parent. The respiration rate per cell of the mutant also increased to twice as much as that of the parent. However, the growth rate of the mutant was lower than that of the parent. Under those conditions, the parent produced more than 40 g/l glutamic acid, while the mutant hardly produced any glutamic acid. Instead the mutant produced 24.6 g/l lactic acid as the main metabolite of glucose. Remarkably, the accumulation of pyruvate and pyruvate-family amino acids, i.e., alanine and valine, was detected in the mutant. On the other hand, the parent accumulated α-ketoglutaric acid and a glutamate-family amino acid, proline, as major by-products. It was concluded that the decrease in the H⁺-ATPase activity caused the above-mentioned metabolic changes in strain F172–8, because a revertant of strain F172–8, R2–1, with a H⁺-ATPase activity of 70% of that of strain ATCC14067, showed a fermentation profile similar to that of the parent. Sequence analyses of the atp operon genes of these strains identified one point mutation in the gamma subunit in strain F172–8.