Abstract
We investigated the effects of iprodione and fludioxonil on the pathogenic yeast Candida albicans. Growth of the wild-type IFO1385 strain of C. albicans was inhibited by both fungicides, while Saccharomyces cerevisiae was basically unaffected by them even at a concentration of 25 μg/ml. Both fungicides stimulated glycerol synthesis in C. albicans but not in S. cerevisiae. The antioxidant α-tocopherol acetate and the cytochrome P-450 inhibitor piperonyl butoxide antagonized the fungitoxicity of iprodione and fludioxonil in C. albicans. It is known that mutations within the histidine kinase NIK1/OS-1 gene confer resistance to iprodione and fludioxonil in Neurospora crassa, while the fungicide-insensitive S. cerevisiae has only one histidine kinase SLN1 gene in its genome. In contrast, C. albicans has three histidine kinase genes, namely CaSLN1, CaNIK1/COS1, and CaHK1, the null mutants of which were found to impair the hyphal formation. Iprodione and fludioxonil were found to suppress filamentation when the IFO1385 strain was incubated on a solid medium containing fetal bovine serum. These observations suggest that iprodione and fludioxonil interfere with the CaNIK1/COS1 signal transduction pathway, resulting in glycerol synthesis stimulation and the inhibition of hyphal formation.
