Candida albicans has a cell-associated ferric-reductase activity which is regulated in response to levels of iron and copper

For survival, pathogenic organisms such as Candida albicans must possess an efficient mechanism for acquiring iron in the iron-restricted environment of the human body. C. albicans can use iron from a variety of sources found within the host. However, it is not clear how biologically active ferrous iron is obtained from these sources. One strategy adopted by some organisms is to reduce iron extracellularly and then specifically transport the ferrous iron into the cell. We have shown that clinical isolates of C. albicans do have a cell-associated ferric-reductase activity. The determination of ferric-reductase activity of cells growing exponentially in either low- or high-iron media over a period of time indicated that C. albicans reductase activity is induced when in low-iron conditions. Moreover, we have demonstrated that C. albicans reductase activity is also regulated in response to the growth phase of the culture, with induction occurring upon exit from stationary phase and maximal levels being reached in early exponential stage irrespective of the iron content of the medium. These results suggest that C. albicans reductase activity is regulated in a very similar manner to the Saccharomyces cerevisiae ferric-reductase. Iron reduction and uptake in S. cerevisiae are closely connected to copper reduction, and possibly copper uptake. In this report we show that iron and copper reduction also appear to be linked in C. albicans. The ferric-reductase activity is negatively regulated by copper. Moreover, quantitative cupric-reductase assays indicated that C. albicans is capable of reducing copper and that this cupric-reductase activity is negatively regulated by both iron and copper. This is the first report that C. albicans has an iron- and copper-mediated ferric-reductase activity.