Stress-induced changes in APR1 expression reveal divergent adaptive responses in Candidozyma auris and Candida...

The identification of factors contributing to pathogenic fitness is essential for understanding the pathogenesis and epidemiology of Candida albicans and Candidozyma auris (Cdm. auris), two pathogenic yeasts associated with high morbidity and mortality in critically ill patients. The APR1 gene, which encodes a vacuolar aspartyl protease, has been implicated in stress responses. This study investigated the association between APR1 transcript levels and traits related to pathogenic fitness in both species. Thermal and osmotic stress resistance, as well as biofilm-associated phenotypes, were evaluated under different conditions. Metabolic activity and biofilm biomass were assessed using MTT and crystal violet assays, respectively. Relative APR1 mRNA expression was analyzed by RT-qPCR under thermal stress (37 °C, 40 °C, and 42 °C), osmotic stress (5% and 10% NaCl), and biofilm-forming conditions. Both species grew at temperatures up to 42 °C, but Cdm. auris showed greater growth capacity in the presence of 10% NaCl. Intra- and interspecies differences in biofilm-associated phenotypes were observed. Under elevated temperatures, Cdm. auris generally exhibited higher metabolic activity, whereas biofilm biomass showed temperature-dependent and species-specific variation. APR1 transcript levels varied depending on the species, strain, and stress condition. In Cdm. auris, APR1 transcript levels increased in strain URM 8618 under thermal stress and in strain B11220 under osmotic stress, as well as under non-biofilm-forming conditions at elevated temperatures. In C. albicans, APR1 transcript levels decreased under thermal stress and biofilm-forming conditions, but moderately increased under osmotic stress. These findings indicate differential APR1 transcriptional responses across species, strains, and stress-associated phenotypes. Further functional studies are required to determine whether these transcriptional changes translate into functional effects.