Breeding of high-pyruvate-producing Torulopsis glabrata with acquired reduced pyruvate decarboxylase

An efficient method for isolation of pyruvate-producing mutants of Torulopsis glabrata IFO 0005 was established. On mutagenesis of the parent strain, mutants requiring acetate for complete growth were isolated. The acetate-leaky auxotrophic mutants demonstrated higher fermentative yields of pyruvate from glucose than the parent strain. Thus, the pyruvate decarboxylase (PDC) activity of mutants requiring acetate for complete growth was lower than that of the parent strain. A decrease in the PDC activity would therefore block the formation of acetate via acetaldehyde and thus increase pyruvate production. Among the mutants, T. glabrata ACII-33 had accumulated free pyruvic acid (60.3 g/l) in 47 h (yield, 67.3%; conversion of pyruvic acid from glucose consumed) in a 3 l jar-fermentor. This yield by strain ACII-33 represented at 15% increase compared to that with the parent strain.