Candida albicans and Yarrowia lipolytica as alternative models for analysing budding patterns and germ tube formation in dimorphic fungi

The site for bud selection and germ tube emission in two yeasts, Candida al bicans and Yarrowia lipolytica, was analysed. Both dimorphic organisms disp lay different patterns of budding, which also differ from those described f or Saccharomyces cerevisiae. C. albicans, which is diploid and (until now) lacks a known sexual cycle, buds in an axial budding pattern. During the ye ast-hypha transition induced by pH, serum, N-acetylglucosamine (GlcNAc) or temperature, germ tube emergence occurs at approximately 50% in a polar man ner, while the other 50% of cells show non-polar germ tube emission. Y. lip olytica, in which most of the natural isolates are haploid and which has a well characterized sexual cycle, buds with a polar budding pattern independ ently of the degree of ploidy. Germ tube emission during the yeast-hypha tr ansition in both haploid and diploid cells generally occurs at the pole dis tal from the division site (bipolar). The addition of hydroxyurea (HU), an inhibitor of DNA synthesis, also produces different effects. In its presenc e, and therefore in the absence of DNA synthesis, the yeast-hypha transitio n is completely abolished in Y. lipolytica. By contrast, in C. albicans ger m tube emission in the presence of HU is similar to that observed in contro l cultures for at least 90 min under induction conditions. These results de monstrate that, rather than a single developmental model, several models of development should be invoked to account for the processes involved in the morphological switch in yeasts (the yeast-hypha transition).