Heavy metals and thiol pool in three strains of Tetracladium marchalianum

Abstract

Growth of three strains of Tetracladium marchalianum was inhibited by Cd-, and, to a lesser extent, by Cu-and Zn-chloride. In the presence of 50 μM Cd(II), all strains increased total thiol and glutathione production to 6, 11, and 21 μmoles · mg−1 dry mass, respectively. Cd(II) also induced the synthesis of one to several compounds reacting with 5,5′-dithio-bis-(2-nitrobenzoic acid). In order to identify buffer-soluble thiolic compounds other than cysteine, γ-EC and γ-ECG (glutathione) were analyzed and confirmed by mass spectrometry. No water soluble sulfides were detectable in any of the culture filtrates, but Cd(II) exposure at a concentration of 50 μM raised sulfide levels in the mycelia of two of the strains between 3 and 7-fold, Cu(II) and Zn(II) had no effect. Energy Dispersive X-ray-analysis (EDX) and Electron Spectrometry-Images (ES-I) of one strain revealed increased levels of Cu and Zn in the cytoplasm and even higher levels in vacuolar precipitates. Zn and Cu are accumulated in the vacuoles as polyphosphates, identified by Electron Energy Loss-Spectrometry (EELS). Cd was found only in the vacuoles.