Saccharomyces cerevisiae and Neurospora crassa contain heavy metal sequestering phytochelatin

In fungi, cellular resistance to heavy metal cytotoxicity is mediated either by binding of metal ions to proteins of the metallothionein type or by chelation to phytochelatin-peptides of the general formula (-Glu-Cys)_n-Gly. Hitherto, only one fungus, Candida glabrata has been shown to contain both metal inactivating systems. Here we show by unambiguous FAB-MS analysis that both a metallothionein-free mutant of Saccharomyces cerevisiae as well as a wildtype strain synthesize phytochelatin (PC₂) upon exposure to 250 M Cd²⁺ ions. The presence of Zn and/or Cu ions in the nutrient broth also induces PC₂ synthesis in this organism. By ¹⁰⁹Cd exchange and subsequent monobromobimane fluorescence HPLC, it could be shown that the presence of Cd²⁺ in the growth medium also induces phytochelatin synthesis in Neurospora crassa, which contains metallothioneins.