The importance of Zn²⁺ ions for fungal growth.

Fungal cells are dependent on divalent cations. We tested the effect of the chelator 1,10-o-phenantroline on bakers yeast and moulds. 100 µM inhibited outgrowth of both. The addition of Zn²⁺ but not Ca²⁺ or Fe²⁺ restored growth indicating the specificity of Zn²⁺ chelation. Experiments with EDTA on yeast essentially showed similar effects. Studies with Saccharomyces cerevisiae showed that spheroplasts expressing *alpha*-galactosidase secreted the protein in equal amounts in the absence or presence of 1,10-o-phenantroline. We concluded that the energy maintenance was not affected significantly by the chelator. In a number of recent experiments the involvement of phospholipase processing in the correct targeting of cell wall mannoproteins has been suggested. In mammals a Zn²⁺ dependent (G)PI-specific phospholipase D has been described. Yeast protoplasts expressing a cell wall protein 2 *alpha*- galactosidase fusion continued to secrete the protein for up to 24 hours in the presence of 1,10-o-phenantroline. We concluded that a Zn²⁺ dependent phospholipase D is not involved in the targeting of wall mannoproteins. In summary, chelation of Zn²⁺ ions has presumably no major effect on fungal energy metabolism, has no effect on the correct processing of cell wall proteins but does inhibit fungal growth. The inhibitory effect may directly be on the cell wall structure and/or cell division.