Hydrogen ions and organic acids secreted by ectomycorrhizal fungi, Pisolithus sp1, are involved in the efficient removal of hexavalent chromium from waste water

Abstract

Pisolithus sp1 is an ectomycorrhizal (ECM) fungi that was chosen during a screening test of six strains of ECM fungi due to its ability to tolerate and remove hexavalent chromium (Cr(VI)). The physiological responses of Pisolithus sp1 to Cr(VI) exposure, the relationship between Pisolithus sp1 and exogenously added organic acids (EAOAs) or Na₃VO₄ (H⁺-ATPase inhibitor) and the ability of Pisolithus sp1 to reduce Cr(VI) in liquid culture were also investigated. Hydrogen ions (H⁺), which were produced directly by Pisolithus sp1, reduced the pH of the medium and played an important role in Cr(VI) reduction; however, Na₃VO₄ significantly inhibited this process and resulted in a decrease in the Cr(VI) reduction rates. Organic acids were secreted after the reduction in Cr(VI) by Pisolithus sp1, and EAOAs did not significantly affect Cr(VI) reduction; those results revealed the secondary role of organic acids in Cr(VI) reduction. The Cr(VI) removal rate of Pisolithus sp1 approached 99% after Cr(VI) treatment for 12 days. Overall, 75% of the Cr(VI) removal was due to extracellular reduction and 24% was due to adsorption. The results of this study provide a strong basis for using Cr(VI)-tolerant and Cr(VI)-reducing fungi, as well as ectomycorrhiza, in the remediation of Cr(VI)-contaminated sites.

Keywords: Cr(VI) reduction; EAOAs; ECM fungi; Organic acids; Pisolithus sp1.