A novel study based on adaptive metal tolerance behavior in fungi and SEM-EDX analysis

Four fungal isolates: Simplicillium chinense (iso 9, accession no. KX425621), Penicillium simplicissimum (iso 10, KP713758), Trichoderma asperellum (iso 11, KP792512), and Coriolopsis sp. (1c3, KM403574) were subjected to a series of induced-tolerance training under high metal concentrations to determine if greater tolerance could be achieved from constant exposure to such conditions. Adaptive tolerance assay (Tolerance Index, TI) and Field-Emission Scanning Electron Microscopy with Energy Dispersive X-ray (SEM-EDX) characterized their metal tolerance. “Untrained” S. chinense, P. simplicissimum and T. asperellum showed tolerance towards 4000–4500 ppm Al(III) (TI: 0.64–0.71), 1000 ppm Cr(III) (0.52–0.83) and Pb(II) (0.32–0.88). With tolerance training, tolerance towards 2000–6000 ppm Al(III), 500–3000 ppm Pb(II) and 2000–3000 ppm Cr(III) were achieved (TI: 0.01–0.82) compared to untrained cultures (0.00–0.59). In contrast, tolerance training for Coriolopsis sp. and P. simplicissimum was less successful, with TI values similar or lower than untrained cultures. SEM-EDX analysis proposed biosorption and bioaccumulation as mechanisms for metal removal. The latter was demonstrated with the removal of Cr(III) and Pb(II) by S. chinense (12.37 and 11.52 mg g⁻¹, respectively) and T. asperellum (10.44 and 7.50 mg g⁻¹). Induced-tolerance training may render benefit in the long run, but this delicate approach is suggestively species and metal dependent.