'Candida albicans PEP12' Is Required for Biofilm Integrity and In Vivo Virulence

To investigate the role of the prevacuolar secretion pathway in biofilm formation and virulence in 'Candida albicans', we cloned and analyzed the 'C. albicans' homolog of the 'Saccharomyces cerevisiae' prevacuolar trafficking gene PEP12. 'C. albicans PEP12' encodes a deduced t-SNARE that is 28% identical to 'S. cerevisiae Pep12p', and plasmids bearing 'C. albicans PEP12' complemented the abnormal vacuolar morphology and temperature-sensitive growth of an 'S. cerevisiae pep12' null mutant. The 'C. albicans pep12' Δ null mutant was defective in endocytosis and vacuolar acidification and accumulated 40- to 60-nm cytoplasmic vesicles near the plasma membrane. Secretory defects included increased extracellular proteolytic activity and absent lipolytic activity. The pep12Δ null mutant was more sensitive to cell wall stresses and antifungal agents than the isogenic complemented strain or the control strain DAY185. Notably, the biofilm formed by the pep12Δ mutant was reduced in overall mass and fragmented completely upon the slightest disturbance. The pep12Δ mutant was markedly reduced in virulence in an in vitro macrophage infection model and an in vivo mouse model of disseminated candidiasis. These results suggest that 'C. albicans PEP12' plays a key role in biofilm integrity and in vivo virulence.