Proso millet peroxidase-mediated degradation and detoxification of Rhodamine B in water

Enzymatic catalysis is a promising approach for the degradation of organic pollutants and peroxidases (PODs) are one of the most common enzyme classes used to degrade organic pollutants. Proso millet peroxidase (PmPOD) is a peroxidase extracted and purified from proso millet bran which is the by-product of proso millet processing. In this study, we investigated the effects of PmPOD on the degradation of typical organic pollutants (Rhodamine B (RhB), bisphenol A, sulfadiazine) for the first time. Moreover, we screened RhB as the substrate with the best degradation effect. The degradation rate of RhB catalyzed by PmPOD (10 nM) reached 99.46% in 30 min under the optimal conditions (pH 5, 30°C, and molar ratio of RhB, H2O2 and HOBT of 1:9.58:1.94 × 10−3). The reaction kinetics parameters of PmPOD-mediated RhB degradation Km, Vmax and kcat were 62.2, 935.7 and 9.357 × 104, respectively. High-performance liquid chromatography analyses confirmed that PmPOD transformed RhB into two new products. Furthermore, toxicological evaluation in Caenorhabditis elegans demonstrated that 10 μg/mL RhB significantly reduced the lifespan by 8.3%, reduced the motility and pharynx-pumping rate compared with the control group, while the 10 μg/mL RhB product had no significant effect on these indexes. These data indicated that the toxicity of RhB disappeared after catalytic degradation by PmPOD. Taken together, these data suggest that catalysis of PmPOD is an effective method for degradation and detoxification of RhB. This study provides a potential candidate method for the biological treatment of RhB, and improves the added value of proso millet bran.