Efficient Biological Decolorization of Malachite Green by Deinococcus wulumuqiensis R12: Process Optimization and Degradation Pathway Analysis

Malachite green (MG) is a toxic triphenylmethane dye widely used in industry, as well as a controversial antimicrobial in aquaculture, leading to environmental concerns. In this study, the conditions for the decolorization of MG by Deinococcus wulumuqiensis R12 were optimized. Under the optimized conditions, a degradation efficiency of 99.30% was achieved for 200 mg/L MG within 30 min, with an initial biomass concentration of 5.5 g/L at 32 °C and pH 5.0. When the initial concentration of MG was increased to 1 g/L, the degradation efficiency surpassed 97% after 2.5 h. Analytical techniques, including UV–VIS, FTIR, GC–MS, and LC–MS analyses revealed that the degradation products included desmethyl-malachite green, di-desmethyl-malachite green, 4-(dimethylamino)benzophenone, and 4-(methylamino)benzophenone, indicating that the MG degradation mechanism of R12 was based on oxidation and demethylation processes. Furthermore, microbial assays confirmed that the byproducts of MG degradation by R12 are much less toxic than the parent compound, indicating the potential of Deinococcus wulumuqiensis R12 as an effective bioremediation agent for MG-contaminated environments.