Innovative insights into hexavalent chromium [Cr(VI)] removal by Cordyceps chanhua: Integrating physicochemical...

Hexavalent chromium [Cr(VI)] contamination poses significant environmental and health challenges, yet the molecular basis of fungal-mediated Cr(VI) detoxification remains insufficiently understood. This study systematically investigates Cr(VI) removal by the edible and medicinal fungus Cordyceps chanhua, integrating physicochemical characterization with molecular functional analysis to clarify detoxification mechanisms. Under optimized conditions (6.0 g/L biomass, pH 5.0, 25 °C), C. chanhua achieved 97.67 % Cr(VI) removal from an initial concentration of 10 mg/L within 24 h, with good selectivity in the presence of common coexisting ions (Na⁺, Ca²⁺, Mg²⁺, Cl^-, and SO₄^2-). Adsorption kinetics followed a pseudo-second-order model, and isotherm data conformed to the Langmuir model, indicating monolayer adsorption. Microscopic and spectroscopic analyses (SEM-EDS, FTIR, XRD) showed chromium accumulation primarily on the mycelial surface, with phosphate groups as the key mediating groups and carboxyl, amino, and phosphate groups contributing to adsorption and reduction. Transcriptomic profiling identified 4817 differentially expressed genes enriched in oxidation-reduction and metal ion response pathways. Four key genes (tde, nbdp, opt, and wd44) were functionally validated through Agrobacterium-mediated genetic manipulation, revealing distinct mechanisms: tde overexpression is significantly associated with enhanced Cr(VI) reduction to Cr(III), nbdp contributes to intracellular chromium accumulation, opt participates in phosphate-related chromium immobilization, and wd44 promotes cell wall-associated chromium retention. Advanced analytical techniques (LC-ICP-MS, TEM-EDS) further confirmed gene-specific functions in extracellular reduction and intracellular chromium immobilization. This integrated approach provides mechanistic insights into fungal Cr(VI) bioremediation at physicochemical and molecular levels, demonstrating the effectiveness of C. chanhua as a biosorbent and identifying molecular targets for engineering strains with enhanced remediation capacity. These findings deepen the understanding of fungal heavy metal detoxification and support the development of bioremediation strategies for contaminated aquatic environments.