Effects of ORF14 gene on melanin expression, fermentation conditions and properties of melanin production in modified strains.

Melanin with antioxidant and antibacterial properties can be used in food, cosmetics, biotechnology, and other fields, but its insolubility become a main challenge hindering for its application. In this study, water-soluble melanin produced by the novel species Streptomyces vilmorinianum YP1 was characterized using scanning electron microscopy (SEM), UVvisible spectroscopy (with an absorption peak at 220 nm), and Fourier transform infrared (FTIR) spectroscopy. The glycosyltransferase gene ORF14 was knocked out, which improved the production of water-soluble melanin by inhibiting competitive pathway. In order to further enhance production of melanin, PlackettBurman and response surface methodology statistical design was employed to screen for key factors and determine the optimal combination. The maximum melanin production (4.00 g/L) was obtained under the conditions: amylodextrine concentration of 40 g/L, soya peptone concentration of 7 g/L, tryptone concentration of 5 g/L, NaCl concentration of 5.4 g/L, pH of 6.7 and temperature of 36 °C for 180 h. The physicochemical properties and bioactivity of melanin were further investigated, revealing that melanin had a good stability across a pH range of 4-12, antioxidant (with a survival rate of over 85 %), and resistance to reducing agents (with a survival rate of over 99 %). The results underscored that S. vilmorinianum YP1 is a promising candidate for water-soluble melanin production.