A genetic screen in combination with biochemical analysis in Saccharomyces cerevisiae indicates that phenazine-1-carboxylic acid is harmful to vesicular trafficking and autophagy

The environmentally friendly antibiotic phenazine-1-carboxylic acid (PCA) protects plants, mammals and humans effectively against various fungal pathogens. However, the mechanism by which PCA inhibits or kills fungal pathogens is not fully understood. We analyzed the effects of PCA on the growth of two fungal model organisms, Saccharomyces cerevisiae and Candida albicans, and found that PCA inhibited yeast growth in a dose-dependent manner which was inversely dependent on pH. In contrast, the commonly used antibiotic hygromycin B acted in a dose-dependent manner as pH increased. We then screened a yeast mutant library to identify genes whose mutation or deletion conferred resistance or sensitivity to PCA. We isolated 193 PCA-resistant or PCA-sensitive mutants in clusters, including vesicle-trafficking- and autophagy-defective mutants. Further analysis showed that unlike hygromycin B, PCA significantly altered intracellular vesicular trafficking under growth conditions and blocked autophagy under starvation conditions. These results suggest that PCA inhibits or kills pathogenic fungi in a complex way, in part by disrupting vesicular trafficking and autophagy.