Mechanism of arsenate resistance in the ericoid mycorrhizal fungus Hymenoscyphus ericae

Arsenate resistance is exhibited by the ericoid mycorrhizal fungus Hymenosc yphus ericae collected from As-contaminated mine soils. To investigate the mechanism of arsenate resistance, uptake kinetics for arsenate (H2AsO4-), a rsenite (H3AsO3), and phosphate (H2PrO4-) were determined in both arsenate- resistant and -non-resistant H. ericae. The uptake kinetics of H2AsO4-, H3A sO3, and H2PO4- in both resistant and non-resistant isolates were similar. The presence of 5.0 muM H2PO4- repressed uptake of H2AsO4- and exposure to 0.75 mM H2AsO4- repressed H2PO4- uptake in both H. ericae. Mine site H. eri cae demonstrated an enhanced As efflux mechanism in comparison with non-res istant H, ericae and lost approximately 90%; of preloaded cellular As (1-h uptake of 0.22 mu mol g(-1) dry weight h(-1) H2AsO4-) over a 5-h period in comparison with non-resistant: H. ericae, which lost 40% of their total abs orbed H2AsO4-. As lost from the fungal tissue was in the form of H3AsO3. Th e results of the present study demonstrate an enhanced H2AsO4- efflux syste m operating in mine site H. ericae as a mechanism for H2AsO4- resistance. T he ecological significance of this mechanism of arsenate resistance is disc ussed.