Living Whole-Cell Biocatalysis for Sustainable and Durable Melanin-Based Textile Coloration

Pigments are widely utilized in industries; however, conventional synthetic pigment production relies on petroleum-based feedstocks, consumes significant energy, and involves toxic chemicals. Although natural pigments provide a sustainable alternative, these systems are constrained by seasonal variability, geographical dependence, and limited scalability. To overcome these limitations, we present a whole-cell biocatalytic approach for melanin synthesis and deposition, wherein recombinant Escherichia coli expressing tyrosinase is employed to convert l-tyrosine into melanin through copper-dependent oxidative polymerization. By harnessing intact microbial cells as self-contained biocatalytic units, this system bypasses the need for enzyme extraction and purification. The process conditions were systematically optimized to maximize melanin yield prior to in situ application on various surfaces, including fabric (cotton) and wood. The successful deposition of melanin was confirmed by ultraviolet-visible-near-infrared reflectance and transmittance measurements, wherein the coated cotton exhibited significantly lower reflectance and transmittance than the uncoated cotton, consistent with the formation of a light-absorbing melanin coating. The uncoated and coated cotton samples were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) to evaluate surface morphology and chemical modifications. SEM images of the uncoated cotton revealed cylindrical fibers in a bundled architecture, whereas the coated cotton exhibited a clear adherence of cells to the surface of the fibers. FTIR spectra showed similar characteristic cellulose peaks for both the uncoated and coated cotton, suggesting minimal changes after coating. XPS analysis indicated the presence of an additional N 1s peak, attributable to the biomacromolecules associated with the adhered bacterial cells. Finally, functional evaluation revealed that the coated cotton exhibited superior photothermal conversion properties, achieving a temperature rise of up to 71 °C under near-infrared laser irradiation compared to minimal heating in uncoated controls. To demonstrate the versatility of the platform, the coating strategy was further extended to wood, where similarly effective melanin deposition was achieved. Taken together, this work establishes a simplified, efficient, and potentially scalable route toward sustainable coloration through living whole-cell engineered biocatalysis.