Metal ion binding byPithomyces chartarum conidia

Summary The binding of metals (Cu, Fe, Mn and Zn) commonly found in soil and decomposing plant material was studied in the saprophytic fungus,Pithomyces chartarum. Binding of metallic divalent cations was pH-dependent and temperature-independent; equilibrium occurred within 10 min in stirred suspensions of conidia, but mycelia had no detectable affinity for the metals. Germ tube emergence and elongation were stimulated by high concentrations of Mn⁺⁺ and Zn⁺⁺, byt not by Cu⁺⁺ or Fe⁺⁺. Metal binding did not obey a simple adsorption isotherm; Scatchard plot analysis indicated two classes of binding sites on the conidial surfaces, one class having association constants about 35-fold greater than those of the other. Calculations based on the conidial surface area as a smooth ellipsoid and the radii of the divalent cations indicated a multilayered coverage of the conidia by the metals at saturation concentrations. Binding sites were stable to boiling, dilute acid and base and lipid solvent extraction. The metals competed with the fungicide, thiabendazole, for binding sites on conidial surfaces.