A newly isolated Streptomyces nigra strain for the biotechnological production of melanin

Melanins are pigments widely distributed in microbial, plant, and animal kingdoms. Their UV-visible light shielding capacity, metal chelation ability, antioxidant, and antimicrobial properties make these pigments suitable for different industrial applications like in cosmetic and bioremediation fields. The actual manufacturing process relies on the extraction from animal tissues like the ink of Sepia officinalis and/or on synthetic chemical procedures. Streptomycetes might be the ideal candidates for the development of biotechnological processes of melanin production due to their ability to produce pigments as secondary metabolites, extracellularly released. Here, a new strain of Streptomyces nigra, capable of efficiently producing eumelanin, was isolated from soil samples in Messina, Sicily, Italy, and characterized first by 16S rRNA analysis and then by whole genome sequencing, with a complete gene clusters analysis. The strain ability of growing and producing melanin was tested on four media, including newly formulated ones, and by also optimizing temperature and pH conditions of growth, a melanin production of 2.45 ± 0.01 g/L was reached. The pigment, once produced under the optimal conditions, was purified and characterized by UV-visible, FT-IR, NMR, and EPR spectroscopy, revealing an eumelanin-like structure. KEY POINTS: • A new Streptomyces nigra strain, MT6, was isolated and identified • A new formulated medium boosted melanin production up to 2.45 g/L • The extracellular pigment was characterized as eumelanin.