Regulation of Aromatic Alcohol Production in Candida albicans

Colonization by the fungal pathogen Candida albicans varies significantly, depending upon the pH and availability of oxygen. Because of our interest in extracellular molecules as potential quorum-sensing molecules, we examined the physiological conditions which regulate the production of the aromatic alcohols, i.e., phenethyl alcohol, tyrosol, and tryptophol. The production of these fusel oils has been well studied for Saccharomyces cerevisiae. Our data show that aromatic alcohol yields for C. albicans are determined by growth conditions. These conditions include the availability of aromatic amino acids, the pH, oxygen levels, and the presence of ammonium salts. For example, for wild-type C. albicans, tyrosol production varied 16-fold merely with the inclusion of tyrosine or ammonium salts in the growth medium. Aromatic alcohol production also depends on the transcription regulator Aro80p. Our results are consistent with aromatic alcohol production--aromatic transaminases (gene products for ARO8 and ARO9), aromatic decarboxylase (ARO10), and alcohol dehydrogenase (ADH)--via the fusel oil pathway. The expression of ARO8, ARO9, and ARO10 is also pH dependent. ARO8 and ARO9 were alkaline upregulated, while ARO10 was alkaline downregulated. The alkaline-dependent change in expression of ARO8 was Rim101 independent, while the expression of ARO9 was Rim101 dependent.