Unraveling the halotolerant degradative machinery of Candida tropicalis JH: a novel biocatalyst for sustainable treatment of hypersaline azo dye effluents.

A novel halotolerant yeast strain, designated as Candida tropicalis JH, was isolated from marine sediment and has been identified as a promising biocatalyst for treating hypersaline azo dye wastewater. Under the optimized conditions (2.0 g/L sucrose, 0.1 g/L (NH4)2SO4, 0.06 g/L yeast extract, 30.0 g/L NaCl, pH 6.0, 35℃, 160 rpm), the yeast JH achieved decolorization rates exceeding 95.0% for the model azo dye Acid Scarlet 3R (concentrations ranged from 100.0 to 800.0 µmol/L) within 12 h, and maintained decolorization rates above 60.0% even at concentrations as high as 1000.0-1600.0 µmol/L. Notably, at salinities up to 110 g/L NaCl, the yeast JH decolorized over 98.0% of 100 µmol/L 3R within 36 h. Additionally, after a 12-h treatment by the yeast JH, the acute toxicity of 100 µmol/L 3R decreased from low toxicity to slight toxicity levels (IR decreased from 33.1% to 17.3%). Enzymatic analyses revealed the involvement of nicotinamide adenine dinucleotide-dependent 2,6-dichlorophenol indophenol (NADH-DCIP) reductase, lignin peroxidase (LiP), manganese peroxidase (MnP) and laccase (Lac) in the degradative process. Transcriptomic profiling further revealed the up-regulation of genes associated with oxidoreductase activity, sugar transport, and key halotolerance mechanisms, including potassium uptake, sodium extrusion, and compatible solute synthesis. These integrated physiological and molecular insights elucidate the degradative machinery of JH, highlighting its dual capacity for efficient dye removal and salt adaptation. The study demonstrates that C. tropicalis JH is a sustainable, halotolerant biocatalyst suitable for the bioremediation of dye-laden hypersaline effluents.