Marine-derived Penicillium oxalicum M6A as a halotolerant biocatalyst for enzymatic biodegradation and detoxification of the azo dye Direct Red 75

The structural complexity and synthetic origin of azo dyes such as Direct Red 75 (DR75) make them environmentally persistent and challenging to remove from industrial effluents.In this study, Penicillium oxalicum M6A, a halotolerant marine-derived fungus isolated from the Nigerian coastline, was evaluated for its capacity to biodegrade and detoxify DR75.The influence of pH, temperature, salt, and dye concentration on degradation efficiency was assessed, along with enzymatic activity. Fourier-transform infrared (FTIR) spectroscopy and gas chromatography–mass spectrometry (GC–MS) analyses were employed to identify degradation products and predict metabolic pathways. Toxicity was determined using three bacterial strains and two crop plant seeds. Optimal degradation was achieved at a pH of 5 (90.37%), a temperature of 35°C (66.82%), a dye concentration of 50 mg/L (91.53%), and a NaCl concentration of 4% (67.08%). Enzymatic assays revealed significant upregulation of laccase (24.17 U/mL), azoreductase (13.14 U/mL), and lignin peroxidase (12.54 U/mL), indicating their involvement in dye breakdown. FTIR analysis confirmed the disappearance of characteristic azo and sulfonic peaks, while GC–MS identified key metabolites such as2,3-dihydrobenzofuran, m-hydroquinone, and 6-ethoxy-6-methyl-2-cyclohexenone. Microtoxicity and phytotoxicity assessments revealed that the degradation products of DR75 by P. oxalicum M6A did not inhibit the bacterial strains and exhibited low toxicity to the seeds of the crop plants used. These findings establish that P. oxalicum M6A can effectively degrade and detoxify DR75, converting it into less toxic metabolites. These observations highlight the biocatalytic potential of P. oxalicum M6A for treating dye-contaminated saline wastewater and encourage further scale-up for environmental applications.