Abstract
Attempts were made to induce auxotrophic mutants from Candida yeasts by ultraviolet light or ethyl met hanesulfonic acid. Among Candida species tested, C. pelliculosa and C. guilliermondii var. membranaefaciens showed higher mutation rate than haploid strain of S. cerevisiae. More than 80% of the auxotrophic mutants of C. guilliermondii var. membranae-faciens were characterized to be amino acid-less, whereas a quarter of C. pelliculosa mutant was nucleic acid base-less. Accumulation of L-threonine by auxotrophic mutants derived from C. guilliermondii var, membranaefaciens by UV-irradiation was studied. One of the isoleucine auxotrophs, strain 150-4, accumulated 1.8mg L-threonine per ml of cane molasses medium, while a tryptophan and isoleucine double auxotroph, strain P120-1, accumulated 2.0mg per ml of the same medium. Enhancement of threonine accumulation was accom-plished by methionine auxotrophs derived from strain P120-1. About 4mg/ml of L-threonine were accumulated by one of the triple auxotrophs (try- ileu- met-), strain MB-21, after 4 days culture in 25% cane molasses medium supplemented with 1.5% urea, 10-3M L-isoleucine, 10-4M L-methionine and 10-3M anthranilic acid.
