Functional and Structural Characterization of Melanin from Brevibacillus invocatus Strain IBA

Melanin is a polyphenol or indolic dark brown to black pigment of macromolecules that has a variety of biological functions including UV defence, desiccation, and oxidation. The pigment is classified as a heterogenic polymer. Analytical characterization of melanin can be difficult due to its heterogeneity. In this study, a newly isolated strain of Brevibacillus invocatus strain IBA capable of extracellular melanin production was grown on nutrient agar and the bacteria were molecularly identified. Chemical and physical methods were used to characterize melanin. The solubility of melanin in organic and inorganic solvents was used to characterise it chemically. According to the UV-visible wavelength scan, physical characterization revealed absorption in the UV region 200 to 300 nm, but declining towards the visible region. Functional group identification of extracted melanin was carried out by FTIR with different stretching vibrations at 3226, 2920, 2849, 1628, 1555, 1340 cm^-1 and weak absorption bands at 1104 and 1015 cm^-1. Structural characterization was carried by SEM of extracted melanin which showed irregular shape and size at different magnifications. The crystallinity of melanin was studied using X-ray crystallography, with a lattice parameter of approximately a = 8.54. The XRD spectrum of the extracted melanin crystallographic pattern revealed peaks at 2θ = 27.32, 31.66, 45.41, 53.84, 53.84, 56.44, 66.18, 73.10, 75.26, and 83.94, which correspond to reflections (111), (200), (220), (311), (222), (400), (331), (420), and (422), respectively. The analytical methods available for melanin analysis are largely complementary, providing detailed knowledge required to draw reliable conclusions about the sample under investigation.