| Candida albicans and Candida glabrata are yeast pathogens that infect humans. The research reported here deals primarily with phenotypic switching in these two organisms. First, to identify the locus that controls white-opaque switching, a reverse genetics strategy was used in which the promoter of a phase-regulated trans-acting factor gene, EFG1, was functionally characterized. It is demonstrated that regulation involves overlapping promoters that control white and opaque phase-specific transcripts, and that a white phase-specific protein complex interacts with a white phase-specific activation region. This work represents the first step in this reverse genetics strategy. Second, experiments were performed to identify the site of C. albicans mating in the human body, since mating has recently been demonstrated to depend on switching. Using a mouse cutaneous model, it is demonstrated that skin facilitates mating. Third, it is demonstrated for the first time that C. glabrata possesses two phenotypic switching systems, the core switching system, in which cells switch between four phenotypes differing in the intensity of brown colony coloration on CuSO4-containing agar, and the irregular wrinkle switching system in which cells switch between smooth or an irregular wrinkle phenotype containing predominantly pseudohyphal cells. Core switching regulates the expression of the genes MT-II and HLP, and the mating type gene MTLalpha1, in a graded manner. Fourth, an analysis of isolates from patients suffering from vaginal C. glabrata infections reveal that both phenotypic switching and mating type switching occur in the host, that switch phenotypes selectively colonize specific anatomical locations, and that both a and alpha strains cause infection. |
