Hexavalent chromium reduction by microbes can mitigate the chromium toxicity to the environment. In the present study Cr[VI] tolerant fungal isolate (CR500) was isolated from electroplating wastewater, was able to tolerate 800 mg/L of Cr[VI. Based on the ITS region sequencing, the isolate was identified as Aspergillus flavus CR500, showed multifarious biochemical (reactive oxygen species, antioxidants response and non-protein thiol) and morphological (protrusion less, constriction and swelling/outwards growth in mycelia) response under Cr[VI] stress. Batch experiment was conducted at different Cr[VI] concentration (0-200 mg/L) to optimize the Cr[VI] reduction and removal ability of isolate CR500; results showed 89.1% reduction of Cr[VI] to Cr[III] within 24 h and 4.9 ± 0.12 mg of Cr per gram of dried biomass accumulation within 144 h at the concentration of 50 mg/L of Cr[VI]. However, a maximum of 79.4% removal of Cr was recorded at 5 mg/L within 144 h. Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy and X-ray diffraction analysis revealed that chromium removal also happened via adsorption/precipitation on the mycelia surface. Fungus treated and without treated 100 mg/L of Cr[VI] solution was subjected to phytotoxicity test using Vigna radiata seeds and result revealed that A. flavus CR500 successfully detoxified the Cr[VI] via reduction and removal mechanisms. Isolate CR500 also exhibited efficient bioreduction potential at different temperature (20-40 °C), pH (5.0-9.0), heavy metals (As, Cd, Cu, Mn, Ni and Pb), metabolic inhibitors (phenol and EDTA) and in sterilized tannery effluent that make it a potential candidate for Cr[VI] bioremediation.
Keywords: Antioxidant; Bioremediation; Chromate reductase; Hexavalent chromium; Phytotoxicity.
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