Characterisation of Pga1, a putative Candida albicans cell wall protein necessary for proper adhesion and biofilm formation

The fungal pathogen Candida albicans is a leading causative agent of death in immunocompromised individuals. Many factors have been implicated in virulence including filamentation-inducing transcription factors, adhesins, lipases and proteases. Many of these factors are glycosylphosphatidylinositol-anchored cell surface antigenic determinant proteins. Pga1 is one such protein shown to be upregulated during cell wall regeneration. The purpose of this study was to characterise the role Pga1 plays by creating a homozygous pga1 null strain and comparing the phenotype with the parental strain. It was observed that the mutant strain showed less oxidative stress tolerance and an increased susceptibility to calcofluor white, a cell surface disrupting agent that inhibits chitin fibre assembly which translated as a 40% decrease in cell wall chitin content. Furthermore, the mutant exhibited a 50% reduction in adhesion and a 33% reduction in biofilm formation compared with the parental strain, which was reflected as a slight reduction in virulence. Our data suggest that Pga1 plays an important role in cell wall rigidity and stability. It was also observed that the pga1 null was over filamentous on both liquid and solid media and exhibited increased resistance to SDS suggesting upregulation of filamentation-inducing genes and cell surface components to partially compensate for the deletion.