Research progress in microbial synthesis of eumelanin

Eumelanin, a natural biological pigment formed by the polymerization of 5, 6-dihydroxyindole and its carboxylic acid derivatives, is ubiquitous in animals and microorganisms. Its highly conjugated molecular structure confers multiple functional properties, including broad-spectrum light absorption, antioxidant activity, free radical scavenging, and metal ion chelation, making it a promising material for applications in biomedicine, functional coatings, and environmental remediation. The conventional production of eumelanin relies largely on extraction from animal tissue or chemical synthesis, which are constrained by limited raw materials and uncontrollable product structures. Recently, microbial cell factory-based biosynthesis of eumelanin has attracted increasing attention due to its environmental sustainability and structural controllability. This review comprehensively summarizes the biosynthetic pathways, strategies for metabolic engineering and genetic engineering, analysis and characterization methods for eumelanin, and discusses future perspectives for the application and development of microbial eumelanin production.