Freshwater Weeds as Low-cost Solid Substrate for the Production of Peroxidase by a Newly Isolated Bacillus flexus from Wastewater

Abstract

Freshwater weeds (Eichhornia crassipes, Lemna minor, Azolla pinnata, Myriophyllum indicum and Nymphoides peltatum) were used as fermentation substrates to increase production of peroxidase enzyme. The pretreated freshwater weeds released sugars which favoured bacterial growth and peroxidase yields. The cellulose content of macroalgae ranged from 15.9±0.42 to 26.4±0.18% and the maximum amount was detected in L. minor (26.4±0.18%). Lignin content was high (8.3±0.4%) in A. pinnata and hemicellulose content was highest (26.5±0.92%) in E. crassipes. Peroxidase production was high in the L. minor biomass (7.28 ±0.41 U/g), followed by E. crassipes (6.72±0.3 U/g). The isolated bacteria C18 produced dye degrading-enzymes such as tyrosinase (2.74±0.3 U/mL), lignin peroxidase (0.71±0.02 U/mL), NADH-DCIP reductase (1.49±0.03 U/mL), laccase (29.8±1.1 U/mL), and azoreductases (35.4±0.15 U/mL). Central composite design and response surface methodology were used to improve peroxidase production by Bacillus flexus. Peroxidase production improved with an increase in initial pH value, low levels of glucose, and ammonium sulphate. B. flexus decolourized methyl red (>75%) and Congo red (>60%) in the culture medium. Lemna minor is a cost-effective culture medium for peroxidase production. The enzyme-based bioremediation reduces toxic pollutants in water systems, thereby potentially reducing health risks due to environmental exposure.