Synthetic Biology–Driven Melanin Deposition for Wood Coating

ABSTRACT Pigments are widely utilized in industries such as textiles, cosmetics, food, and packaging. However, conventional synthetic pigment production relies on petroleum-based feedstocks, consumes significant energy, and involves toxic chemicals raising environmental and safety concerns. Natural pigments offer a sustainable and biodegradable alternative, yet their large-scale application is hindered by limited availability, batch variability, and geographical dependence. To overcome this, microbial biosynthesis has attracted attention as a controllable and scalable route for pigment production independent of environmental fluctuations. Nevertheless, most existing approaches retain multistep workflows – pigment synthesis, extraction, purification, and application. This compromises process efficiency and reproducibility. Herein, we present a whole-cell biocatalytic approach for melanin synthesis and deposition, wherein recombinant E. 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. Prior to applying the culture media containing melanin on material surfaces such as cotton and wood, the process conditions were optimized to enhance melanin yield. Subsequently, the material surfaces incubated in the melanin culture medium were characterized for their surface morphology and chemical modifications through scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The color fastness properties of the material were also evaluated in the presence of water and detergents and subsequently improved through post-treatment processes. In addition, the melanin-coated cotton demonstrated enhanced photothermal performance compared to uncoated controls. All these taken together, this work establishes a simplified and potentially scalable route toward sustainable pigment production and direct application through enzyme-driven in situ biocatalysis on various material surfaces.