The Candida albicans vacuole is required for differentiation and efficient macrophage killing

Yeast-hypha differentiation is believed to be necessary for the normal progression of Candida albicans infections. The emergence and extension of a germ tube from a parental yeast cell are accompanied by dynamic changes in vacuole size and morphology. Although vacuolar function is required during this process, it is unclear if it is vacuolar expansion or some other vacuolar function that is important. We previously described a C. albicans vps11Delta mutant which lacked a recognizable vacuole compartment and with defects in multiple vacuolar functions. These include sensitivities to stress, reduced proteolytic activities, and severe defects in filamentation. Herein we utilize a partially functional VPS11 allele (vps11hr) to help define which vacuolar functions are required for differentiation and which influence interaction with macrophages. Mutant strains harboring this allele are not osmotically or temperature sensitive and have normal levels of secreted aspartyl protease and carboxypeptidase Y activity but have a fragmented vacuole morphology. Moreover, this mutant is defective in filamentation, suggesting that the major role the vacuole plays in yeast-hypha differentiation may relate directly to its morphology. The results of this study support the hypothesis that vacuole expansion is required during germ tube emergence. Both vps11 mutants were severely attenuated in their ability to kill a macrophage cell line. The viability of the vps11delta mutant was significantly reduced during macrophage interaction compared to that in the control strains, while the vps11hr mutant was unaffected. This implies some vacuolar functions are required for Candida survival within the macrophage, while additional vacuolar functions are required to inflict injury on the macrophage.