Coupling azo dye biotransformation with lipid biosynthesis in oleaginous Trichosporonales

This study evaluated the dual-functional potential of Trichosporonales yeasts for integrating textile dye remediation with lipid production within a wastewater biorefinery framework. Five strains from the genera Apiotrichum and Cutaneotrichosporon were screened for their ability to decolorize Reactive Black 5 while accumulating intracellular lipids. Among them, Apiotrichum domesticum JCM9580 showed the best overall performance due to its high lipid productivity, efficient dye removal, and stable yeast-like morphology, representing an operational advantage over filamentous growth forms. Results revealed an inverse relationship between lipid biosynthesis and dye decolorization, regulated by a classical C/N metabolic switch. High C/N ratios activated the lipogenic program, converting the cell into a strong sink for reducing equivalents and limiting decolorization, whereas low C/N conditions suppressed lipogenesis, preserving reducing power for rapid and nearly complete dye removal. UV-is, FTIR, and GC-S analyses indicated that reductive azo bond cleavage is an early step during decolorization, although the complete biodegradation pathway remains unresolved. In addition, Reactive Black 5 exposure increased fatty acid polyunsaturation, improving biodiesel cold-flow properties. Notably, A. domesticum achieved a cold filter plugging point of -3.86 °C. Phytotoxicity assays showed that untreated RB5 completely inhibited germination (0% GI), whereas yeast-treated samples reached GI values of 0.28-0.30 (20% dilution), representing a substantial detoxification; further dilution to 10% eliminated all inhibitory effects. Overall, these findings establish a basis for future bioprocess optimization within wastewater biorefinery systems.