Integrated biosorption and bioreduction of hexavalent chromium using Fusarium species under optimized process...

Fungal biosorption and bioreduction of hexavalent chromium (Cr(VI)) provide a sustainable and cost-effective alternative to traditional physicochemical methods by utilizing microbial enzymatic pathways for detoxification. Fusarium verticillioides and Fusarium oxysporum were isolated and tested for their ability to remove Cr(VI) from aqueous solutions. Biomass and filtrate obtained after growth of F. verticillioides at pH 2 showed a maximum Cr(VI) removal achieving 77% and 79% removal, respectively.While biomass and filtrates obtained after growth of F. oxysporum at pH4 showed the optimal Cr(VI) removal (69%) for biomass and (97%) for filtrate, respectively. Increasing inoculum size up to 38 × 10⁸ CFU enhanced Cr(VI) reduction efficiency, but removal decreased with higher Cr(VI) concentrations, with no removal observed at 60 mg/l. Removal efficiency also increased significantly with incubation time up to five days. Scanning electron microscopy revealed structural changes in fungal biomass associated with biosorption and reduction of Cr(VI) to the less toxic Cr(III), supported by detection of chromate reductase activity in fungal exo- and endo-filtrates as well as membrane debris. Atomic absorption spectroscopy indicated that F. verticillioides and F. oxysporum converted approximately 95% and 78% of Cr(VI) to Cr(III), respectively, suggesting these fungi offer eco-friendly bioremediation strategies by combining cell-wall biosorption with enzymatic bioreduction mechanisms to transform toxic chromium into less harmful forms.