Marine-derived Streptomyces sp. isolated from the Persian Gulf as a novel source of melanin

In this study, the structure and biological properties of melanin pigment produced by Streptomyces strain SEA5 isolated from Persian Gulf sediments were investigated. This strain was cultured in an enriched culture medium (L-tyrosine, meat extract). Pigment production was also performed in culture media containing different sources of amino acid L-tyrosine such as soybean meal. Pigment extraction was performed using hydrochloric acid (6 M). In order to investigate its physicochemical nature, TLC, HPLC, UV-Vis spectroscopy, FTIR and 1 H NMR analysis was performed. On the other hand, strong UV absorption with SPF, antioxidant activity and cytotoxicity assay of this pigment were also studied. The results showed that strain SEA5 was well grown and melanized well (1.5 g/L) in medium containing L-tyrosine. It was 1.36 g/L when cultured in medium containing soybean meal. The UV-vis spectrum had an absorption peak at 225 nm. FTIR identified the functional groups of eumelanin with very high peaks at 3414.46 cm-1 (N-H group) and 1650-1540 cm-1 (CO and CN vibrations). Also, the ¹HNMR spectrum showed several peaks between 6.9 and 8.0 ppm, indicating aromatic protons. On the other hand, the extracted pigment had an SPF of 22.55 and showed significant antioxidant activity with 60-77 % reduction of DPPH radicals. The pigment in the formulation selectively inhibited the growth of A375 melanoma cells (IC50- 79.82 μg/mL), whilst it was non-toxic when tested against normal human dermal fibroblasts and HaCaT keratinocytes. Overall, these findings suggest the potential of SEA5-derived melanin as a human skin care product, pharmaceutical product and antioxidant material.