ABSTRACT
Purpose of Review: Failure of antifungal treatment is alarmingly common in patients infected with Candida albicans isolates that test as susceptible in vitro. This means that clinical susceptibility tests have limited predictive value for treatment success. To guide the improvement of patient outcomes, we must understand the effects of environmental and metabolic states on drug responses. Recent Findings: Lab conditions often deviate from host environments, and current susceptibility testing standards ignore slow-growing, tolerant phenotypes; both factors may contribute to antifungal treatment failure. Metabolomic studies reveal that strain background, nutrient availability, and drug exposure influence the metabolic state of C. albicans cells; similarly, the metabolic state influences drug susceptibility. Summary: Identifying tolerant strains in the clinic may improve patient outcomes. Studies that analyze the effects of essential but limited nutrients have the potential to improve the avoidance of persistent candidiasis and to reduce the frequency of antifungal treatment failures. Here, we highlight literature that explores the effect of drug exposure and antifungal drug resistance status on the C. albicans metabolome. Similar analyses need to be carried out relative to antifungal drug tolerance. Additionally, we focus on the biological relevance of four essential small molecules-iron, zinc, phosphate, and sphingolipids-to antifungal tolerance and resistance.
ABSTRACT
When glucose is available, Saccharomyces cerevisiae prefers fermentation to respiration. In fact, it can live without respiration at all. Here, we study the role of respiration in stress tolerance in yeast. We found that colony growth of respiratory-deficient yeast (petite) is greatly inhibited by canavanine, the toxic analog of arginine that causes proteotoxic stress. We found lower amounts of the amino acids involved in arginine biosynthesis in petites compared with WT. This finding may be explained by the fact that petite cells exposed to canavanine show reduction in the efficiency of targeting of proteins required for arginine biosynthesis. The retrograde (RTG) pathway signals mitochondrial stress. It positively controls production of arginine precursors. We show that canavanine abrogates RTG signaling especially in petite cells, and mutants in the RTG pathway are extremely sensitive to canavanine. We suggest that petite cells are naturally ineffective in production of some amino acids; combination of this fact with the effect of canavanine on the RTG pathway is the simplest explanation why petite cells are inhibited by canavanine. Surprisingly, we found that canavanine greatly inhibits colony formation when WT cells are forced to respire. Our research proposes a novel connection between respiration and proteotoxic stress.
