Peroxisomal fatty acid beta-oxidation is not essential for virulence of Candida albicans

Phagocytic cells form the first line of defense against infections by the human fungal pathogen Candida albicans. Recent in vitro gene expression data suggest that upon phagocytosis by macrophages, C. albicans reprograms its metabolism to convert fatty acids into glucose by inducing the enzymes of the glyoxylate cycle and fatty acid P-oxidation pathway. Here, we asked whether fatty acid P-oxidation, a metabolic pathway localized to peroxisomes, is essential for fungal virulence by constructing two C. albicans double deletion strains: a pex5 Delta/pex5 Delta mutant, which is disturbed in the import of most peroxisomal enzymes, and a fox2 Delta/fox2 Delta mutant, which lacks the second enzyme of the beta-oxidation pathway. Both mutant strains had strongly reduced beta-oxidation activity and, accordingly, were unable to grow on media with fatty acids as a sole carbon source. Surprisingly, only the fox2 Delta/fox2 Delta mutant, and not the pex5 Delta/pex5 Delta mutant, displayed strong growth defects on nonfermentable carbon sources other than fatty acids (e.g., acetate, ethanol, or lactate) and showed attenuated virulence in a mouse model for systemic candidiasis. The degree of virulence attenuation of the fox2 Delta/fox2 Delta mutant was comparable to that of the icl1 Delta/icl1 Delta mutant, which lacks a functional glyoxylate cycle and also fails to grow on nonfermentable carbon sources. Together, our data suggest that peroxisomal fatty acid beta-oxidation is not essential for virulence of C. albicans, implying that the attenuated virulence of the fox2 Delta/fox2 Delta mutant is largely due to a dysfunctional glyoxylate cycle.