Binding of micro-nutrients to the cell wall of the fungus Schizophyllum commune

Abstract

The cell wall fulfils several functions in the biology of fungi. For instance, it provides mechanical strength, interacts with the (a)biotic environment, and acts as a molecular sieve. Recently, it was shown that proteins and β-glucans in the cell wall of Schizophyllum commune bind Cu²⁺. We here show that the cell wall of this mushroom forming fungus also binds other (micro-)nutrients. Ca²⁺, Mg²⁺, Mn²⁺, NO₃^–, PO₄^3-, and SO₄^2- bound at levels > 1 mg per gram dry weight cell wall, while binding of BO₃^-, Cu²⁺, Zn²⁺ and MoO₄^2- was lower. Sorption of Ca²⁺, Mn²⁺, Zn²⁺ and PO₄^3- was promoted at alkaline pH. These compounds as well as BO₃^3-, Cu²⁺, Mg²⁺, NO₃^–, and SO₄^2- that had bound at pH 4, 6, or 8 could be released from the cell wall at pH 4 with a maximum efficiency of 46–93 %. Solid-state NMR spectroscopy showed that the metals had the same binding sites as Cu²⁺ when a low concentration of this ion is used. Moreover, data indicate that anions bind to the cell wall as well as to the metal ions. Together, it is shown that the cell wall of S. commune binds various (micro-)nutrients and that this binding is higher than the uptake by hyphae. The binding to the cell wall may be used as a storage mechanism or may reduce availability of these molecules to competitors or prevent toxic influx in the cytoplasm.