Identification of Candida albicans genes that induce Saccharomyces cerevisiae cell adhesion and morphogenesis.

Morphogenesis and adhesion to host tissues and medical devices contribute to the virulence of Candida albicans, the most common fungal pathogen isolated from humans. However, identification of molecular mechanisms of C. albicans adhesion and morphogenesis has been impaired by the lack of effective molecular and genetic tools available for this organism. Saccharomyces cerevisiae provides an attractive model system for studying C. albicans adhesion and morphogenesis because of its well-characterized genetics and gene expression systems. To gain insight into the genetic mechanisms of C. albicans adhesion and morphogenesis, we used a parallel plate flow chamber to screen and quantitatively characterize attachment to polystyrene of an adhesion-deficient nonfilamentous flo8Delta S. cerevisiae strain expressing a C. albicans genomic library. We identified six C. albicans genes that are capable of promoting cell adhesion and pseudohyphal development in S. cerevisiae. We also analyzed the ability of these adhesion-promoting genes to regulate the expression of FLO11, which encodes an endogenous S. cerevisiae adhesin. One C. albicans gene, EAP1, appears to directly mediate adhesion and morphogenesis while the remaining five (EAP2, SWI1, MSB1, AAF1, and TEC1) upregulate expression of endogenous S. cerevisiae adhesins. These results suggest that S. cerevisiae is a useful system for molecular characterization of factors that regulate C. albicans adhesion and morphogenesis and that parallel plate flow chamber-based adhesion assays can be used in conjunction with genetic screens to identify molecular mechanisms regulating fungal cell adhesion.