Breeding of high-pyruvate-producing Torulopsis glabrata and amino acid auxotrophic mutants

An efficient method for the isolation of pyruvate-producing mutants of Torulopsis glabrata IFO 0005 was established. On mutagenesis of the parent strain, mutants requiring polypeptone for complete growth were isolated. Seven mutants among one hundred auxotrophs produced higher concentrations of pyruvate than the parent strain. Among them, arginine (L-Arg) auxotrophic mutants and an isoleucine (L-Ile) and valine (L-Val) double auxotrophic mutant exhibited higher fermentative production of pyruvate from glucose than the parent strain. T. glabrata X-15 and X-17 required L-Arg for complete growth. T. glabrata X-68 absolutely required L-Ile and L-Val for complete growth. These three strains (X-15, X-17 and X-68) have more than 10% higher yields of pyruvate than the parent strain. Among them, the best strain regarding pyruvate productivity, T. glabrata X-15, accumulated 59.5 g/l free pyruvic acid (yield, 60.1%; conversion to pyruvic acid of added glucose in 43 h) on a 3-l jar-fermentor scale. This yield with strain X-15 represented a 12% increase compared to that obtained with the parent strain.