Biosynthesis of melanin from lignin hydrolysates by metabolically engineered Cupriavidus necator

Melanin is an advanced polymer with exceptional properties, widely used across cosmetics, pharmaceuticals, environmental applications, and more. However, its broader use is constrained by high production costs and limited availability. Lignin, the most abundant and renewable aromatic compound in nature, presents a promising alternative for synthesizing melanin. This study focuses on converting plentiful and cost-effective lignin into melanin through the metabolic engineering of Cupriavidus necator H16. By constructing and optimizing metabolic pathways, engineered C. necator strains were developed to synthesize melanin from lignin monomers and lignin hydrolysates. Using substrates like p-coumaric acid, caffeic acid, ferulic acid, and lignin hydrolysates, the resting cell method with C. necator produced 0.86, 1.00, 0.52, and 0.32 g L^-1 of melanin, respectively. The purified melanin was analyzed and identified spectrally, revealing characteristics of isomelanin. Furthermore, sun protection factor studies demonstrated that the produced melanin offered significant UV protection. The use of engineered C. necator to convert abundant lignin hydrolysates into melanin holds great promise for reducing production costs and expanding its applications.