ABSTRACTSterol import has been characterized under various conditions in three distinct fungal species, the model organismSaccharomyces cerevisiaeand two human fungal pathogensCandida glabrataandCandida albicans, employing cholesterol, the sterol of higher eukaryotes, as well as its fungal equivalent, ergosterol. Import was confirmed by the detection of esterified cholesterol within the cells. Comparing the three fungal species, we observe sterol import under three different conditions. First, as previously well characterized, we observe sterol import under low oxygen levels inS. cerevisiaeandC. glabrata, which is dependent on the transcription factor Upc2 and/or its orthologs or paralogs. Second, we observe sterol import under aerobic conditions exclusively in the two pathogenic fungiC. glabrataandC. albicans. Uptake emerges during post-exponential-growth phases, is independent of the characterized Upc2-pathway and is slower compared to the anaerobic uptake inS. cerevisiaeandC. glabrata. Third, we observe under normoxic conditions inC. glabratathat Upc2-dependent sterol import can be induced in the presence of fetal bovine serum together with fluconazole. In summary,C. glabrataimports sterols both in aerobic and anaerobic conditions, and the limited aerobic uptake can be further stimulated by the presence of serum together with fluconazole.S. cerevisiaeimports sterols only in anaerobic conditions, demonstrating aerobic sterol exclusion. Finally,C. albicansimports sterols exclusively aerobically in post-exponential-growth phases, independent of Upc2. For the first time, we provide direct evidence of sterol import into the human fungal pathogenC. albicans, which until now was believed to be incapable of active sterol import.
Development of a Stoichiometric Model for Estimation of Metabolic Fluxes in Saccharomyces cerevisiae during Tequila Production
