Optimization of decolorization conditions and degradation pathway of malachite green by Penicillium citrinum strain YR02.

Malachite green (MG), a widely used biocide and dye, requires effective remediation due to its pronounced toxicity and environmental persistence. This study investigated MG decolorization by Penicillium citrinum strain YR02, optimizing decolorization conditions using Plackett-Burman design (PBD) and Uniform Design (UD) methodologies, probing the degradation mechanism, and assessing the toxicity of degradation products. Under optimal conditions (starch 11.6 g/L, peptone 6.3 g/L, MgSO4·7H2O 0.5 g/L, CuCl2·2H2O 0.03 g/L, pH 6.4, 28 °C), with 0.5 mL of a 1 × 106 spores/mL inoculum suspension and a shaking speed of 160 rpm, strain YR02 achieved 100% decolorization of 0.02 g/L MG within 120 h. Morphological observations indicated that MG was initially adsorbed by fungal hyphae to form pigmented pellets, where it was subsequently degraded primarily by laccase activity. Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analyses identified 4-dimethylaminobenzophenone, Michler's ketone, and dimethylaminobenzoic acid as primary intermediates, which were further metabolized into smaller compounds. Phytotoxicity tests demonstrated that the degradation products were less toxic than untreated MG. These results indicate that P. citrinum YR02 is an efficient and environmentally compatible strain for MG biodegradation. Future work should emphasize immobilizing the strain to enhance reusability and conducting pilot-scale trials for application to dye-contaminated wastewater.