"Functional profiling and computational optimization of production of extracellular melanin from endophytic Pseudomonas plecoglossicida SSSK-2 isolated from Neolamarckia cadamba".

Melanin is a multifunctional biopolymer with a wide range of applications in biomedical, cosmetic, and environmental industries. While most melanin-producing bacteria are isolated from environmental sources, endophytic bacteria remain largely unexplored despite their metabolic adaptability and potential for high-yield production. This study investigates extracellular melanin biosynthesis by the endophytic bacterium Pseudomonas plecoglossicida SSSK-2, isolated from Neolamarckia cadamba. Melanin production was optimized in submerged culture using an Artificial Neural Network (ANN) linked with a Genetic Algorithm (GA), yielding 7.4 ± 0.39 g/L in seven days. The produced melanin was slightly soluble in water and exhibited a porous, irregular surface. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the presence of functional groups, including NH, OH, COO⁻, CH₃, and CH₂. Its solubility profile, UV-Visible spectral properties, FTIR characteristics, resistance to kojic acid inhibition, and absence of the tyrosinase gene suggest the pigment is likely pyomelanin. It demonstrated a Sun Protection Factor (SPF) of 102.84 ± 6.13 at a concentration of 0.2 mg/mL. It also exhibited 71.8 ± 6.0% free radical scavenging activity at 80 µg/mL, which is slightly lower than the 77.12% activity of ascorbic acid at the same concentration. The highest chelating activity was 64.6 ± 1.67% at a concentration of 200 µg/mL. For anti-inflammatory activity, melanin showed 69.69 ± 1%, lower than the 82 ± 2% recorded for diclofenac sodium at 50 µg/mL. The cytotoxicity of melanin, determined through the brine shrimp nauplii assay, was 1121 µg/mL, exceeding the safe threshold of 1000 µg/mL. These findings suggest that melanin has promising applications in biomedicine, radioprotection, cosmetics, and bioremediation.