Decolourization and biodegradation of methylene blue dye by a ligninolytic enzyme-producing Bacillus thuringiensis: Degradation products and pathway

Abstract

In this study, a ligninolytic enzyme-producing strain F5 was isolated and identified as Bacillus thuringiensis, which can efficiently degrade methylene blue (MB) dye. The optimal pH, temperature, rotation speed, NaCl concentration, and inoculum of strain F5 for MB degradation were pH 6.0, 30 °C, 140 rpm, 10 g/L NaCl, 4% inoculum (v/v), and the strain F5 had salt tolerance, the MB decolorization rate reached 95% after 12 h. The degraded products were characterized by UV–vis, FT-IR, and GC-MS. Based on products analysis, four different intermediates were identified, and a new pathway for the degradation of MB was proposed. The degradation of MB by strain F5 was due to the synergistic effects of laccase (Lac), manganese peroxidase (MnP), lignin peroxidase (LiP), and NADH-DCIP reductase; among them, Lac and MnP were the key enzymes. The phytotoxicity results showed that MB degraded metabolites' toxicity was lower than that of the parent compound, indicating that the strain F5 had a detoxification effect on MB dyes.