Mechanism of Arsenate Resistance in the Ericoid Mycorrhizal Fungus Hymenoscyphus ericae

Arsenate resistance is exhibited by the ericoid mycorrhizal fungus Hymenoscyphus ericae collected from As-contaminated mine soils. To investigate the mechanism of arsenate resistance, uptake kinetics for arsenate (H(2)AsO(4)(−)), arsenite (H(3)AsO(3)), and phosphate (H(2)PO(4)(−)) were determined in both arsenate-resistant and -non-resistant H. ericae. The uptake kinetics of H(2)AsO(4)(−), H(3)AsO(3), and H(2)PO(4)(−) in both resistant and non-resistant isolates were similar. The presence of 5.0 μm H(2)PO(4)(−) repressed uptake of H(2)AsO(4)(−) and exposure to 0.75 mm H(2)AsO(4)(−) repressed H(2)PO(4)(−) uptake in both H. ericae. Mine site H. ericae demonstrated an enhanced As efflux mechanism in comparison with non-resistant H. ericae and lost approximately 90% of preloaded cellular As (1-h uptake of 0.22 μmol g(−1) dry weight h(−1) H(2)AsO(4)(−)) over a 5-h period in comparison with non-resistant H. ericae, which lost 40% of their total absorbed H(2)AsO(4)(−). As lost from the fungal tissue was in the form of H(3)AsO(3). The results of the present study demonstrate an enhanced H(3)AsO(3) efflux system operating in mine site H. ericae as a mechanism for H(2)AsO(4)(−) resistance. The ecological significance of this mechanism of arsenate resistance is discussed.