Production, characterization and biochemical properties of melanin from crude salt-associated Hortaea sp. strain PMGTC8

Microbial melanin is a natural macromolecule offering multifaceted use in the environment and biotechnology. Considering this, the current study aimed to optimize physicochemical conditions for maximum melanin production by crude salt-associated Hortaea sp. strain PMGTC8 and to evaluate its biochemical properties. Hortaea cells grew in a 1.5 L fermenter with a maximum of 6.7 ± 1.01 g/L of biomass and 10.1 ± 1.58 mg/L melanin yield in the presence of glucose and glycerol. The acid-precipitated melanin was maximally soluble in alkali. UV–Vis analysis showed a prominent peak at 208 nm, while the fluorescence spectrum revealed peaks at 270, 350, 410, 475, 530 and 575 nm, indicating the conjugated nature of purified melanin. Carbon, hydrogen, nitrogen and sulfur analysis revealed 1,8-dihydroxy naphthalene (DHN) melanin, and the scanning electron micrograph showed spherical morphology. Infrared analyzed NH, CH, NH₂, CO, CH and CH₃-CH₃ groups in melanin. Further, melanin exhibited 64.72 ± 0.64% DPPH (1,1-diphenyl-2-picryl hydrazyl) radical scavenging activity at 100 µg/mL, 61.76 ± 5.26% antihemolytic at 50 µg/mL and 50.33 ± 2.89% chromium adsorption capacity for 5 ppm chromium concentration. Furthermore, melanin was maximally active against Pseudomonas aeruginosa. In addition, the prospects of melanin being used as a fluorescent probe for the detection of picric acid in fluorescence turn-off mode were justified. The study concluded that melanin from Hortaea sp. strain PMGTC8 could be explored from the view of biotechnological and environmental perspectives.

Graphical abstract