Iron oxide nanoparticles immobilized Aspergillus flavus manganese peroxidase with improved biocatalytic, kinetic, thermodynamic, and dye degradation potentialities

Manganese peroxidase (MnP) has gained significant attention for treating textile waste due to its ability to oxidize and detoxify a wide range of recalcitrant xenobiotics, including synthetic dyes. MnP was isolated from a solid-state culture of Aspergillus flavus using pre-optimized conditions of 5 g wheat bran (66% moisture content), pH 4.5, temperature 30 ℃, carbon source: glucose 2%, nitrogen source: yeast extract 0.02%, 5 ml of homogenous fungal spore suspension and fermentation period of 5 days. The extracted MnP was partially purified using ammonium sulfate precipitation and immobilized on iron oxide nanoparticles. Soluble and immobilized MnP showed the maximum catalytic potential at 35 ℃ and 50 ℃, and optimum pH of 4.0 and 5.0, respectively. Vmax and Km for free MnP were 0.126 U/mg and 0.0886 mM, and 0.140 U/mg and 0.704 mM for the immobilized MnP, respectively. Thermodynamic parameters, including Ea, ΔH*, ΔG*, ΔS* were also investigated for free and immobilized MnP. Finally, the soluble and immobilized MnP were exploited for catalytic degradation of two textile dye pollutants, Direct red 31 and Acid black 234. Free MnP catalyzed 94% decolorization of Direct red 31, while 100% decolorization was achieved with immobilized MnP. On the other hand, Acid black 234 showed 85% and 92% decolorization with free and immobilized MnP, respectively. The magnetically separable immobilized MnP was more thermally stable, can work over a wider pH and temperature range, and be more catalytically vigorous than its free counterpart.