Genetic and biochemical studies on mannose-negative mutants with colonial morphological alterations.

Four mannose mutants of Saccharomyces cerevisiae are described. In addition to their inability to grow on mannose as sole carbon and energy source, the mutants exhibit a distinct colonial morphological alteration. The isolates form hard colonies when grown on agar and exhibit extreme flocculation in broth. These organisms can catabolize mannose, but only form one-half the mannan found in the wild-type yeasts.