Characterization of extracellular pigments from actinomycetes isolated from different sources and investigation of some biofunctional properties

In this study, a total of 175 isolates, including 130 actinomycetes isolated from 49 soil and 4 mud samples collected from different regions of Turkey (Burdur, Denizli, Kütahya, Balıkesir) and 45 actinomycetes obtained from previous projects, were evaluated for extracellular pigment production. Among the 71 isolates showing pigment production, Streptomyces griseorubens K3, Streptomyces variabilis B23, and Streptomyces variabilis B25 strains were selected, and their cultural and morphological characteristics were examined before species identification. Pigment extracts obtained from the culture medium at the end of the stationary phase were subjected to detailed structural analysis. UV-Vis, FT-IR, ¹H NMR, SEM-EDS, and LC-MS Q-TOF analyses were performed for the structural characterization of melanin pigments. It was determined that the extracts obtained from all strains contained eumelanin, pheomelanin, and neuromelanin components. Melanin extracted from the Streptomyces variabilis B23 strain exhibited antibacterial activity against all Gram-negative and Gram-positive bacteria tested. Melanin extracted from the Streptomyces variabilis B25 strain was tested on SW-620 colon cancer and CCD18Co normal colon cell lines and found to have IC50 values greater than 1000 µg/mL. This study is pioneering in the literature in that it is the first to extract melanin from S. griseorubens and S. variabilis species and to reveal the structural diversity of Streptomyces melanins and their antibacterial and anticancer properties. The obtained data provide important insights into the biotechnological potential of naturally derived melanin pigments.