The inhibitory effect of cerulenin to yeasts is fungicidal

Abstract

Fatty acid biosynthesis plays a significant role in the growth and survival of diverse organisms. In yeasts, the de novo fatty acid synthesis (FAS) pathway produces and regulates essential fatty acid species such as saturated (SFA) and unsaturated (UFA) fatty acids that are required for generation and maintenance of cell membranes. Inhibition of enzymes in this pathway, such as fatty acid synthase and fatty acid desaturase, impede yeast cell growth unless appropriate exogenous fatty acids are provided.^1,2 Although, the fatty acid biosynthesis pathway is essential to yeast cells, exploration of this pathway for combating fungal infections has been largely neglected. We and others have shown that deletion of a fatty acid synthase dramatically attenuates the virulence of the yeast Candida parapsilosis 2 and Candida albicans.¹ Significantly, our data has revealed that inhibition of FAS enzymes results in the hypersensitivity of the yeast to serum, indicating that targeting this pathway is potentially an ideal way to combat systemic yeast infections.² We demonstrated that using the minimal inhibitory concentration of cerulenin, a fatty acid synthase inhibitor, we could kill the wild type yeast cells in serum.² Thus, the inhibitory effect of cerulenin (ie. blockade of the FAS pathway) on the yeast cells is fungicidal.

Additionally, as cerulenin is a specific inhibitor of fatty acid synthase, it has been extensively used to block the FAS pathway. Importantly, its use experimentally for blockade of de novo FAS and forcing yeast cells to utilize stored lipids for growth might lead to unintended results as the consequence of cerulenin induced cell death.^3,4 Indeed, we have observed that inhibition of wild type Candida yeast cells with cerulenin led to significant rates of cell death within hours of incubation in standard media such as YPD (yeast extract, peptone, glucose) or YNB (yeast nitrogen base, with 1% glucose) (Fig. 1). These results were confirmed using a C. parapsilosis FAS2 mutant (Fig. 1C). Notably, inhibition of de novo fatty acid biosynthesis has also been well described as fungicidal in Saccharomyces cerevisae⁵ in YPD media. Thus, using cerulenin to block fatty acid biosynthesis raises important questions regarding the lethal effect of this compound to yeasts and literature presenting data obtained with this compound should be assessed critically for the potential impact of cell death.

Figure 1.

Cerulenin kills yeast cells. The addition of cerulenin to YNB with 1% glucose is fungicidal to wild type (WT) Candida parapsilosis yeast. (A) WT yeast cells without cerulenin have a high viability. (B) WT yeast cells incubated with cerulenin have significantly reduced viability, which is similar to that of (C) C. parapsilosis FAS2 gene disruptants (approximately 36% and 38% viability, respectively). Yeast cells were stained with vital dye Sytoxgreen after 12h of incubation. Cerulenin (Sigma) 10 µg/ml was used. Scale bar: 15µm.