Melanin
Melanins are macromolecules that are synthesised during phenolic and/or indolic chemicals being oxidatively polymerized. These hydrophobic pigments are negatively charged, which are found throughout the biological system in a wide range and take part in processes like structure, colouring, free radical scavenging, radiation resistance, and thermoregulation. Many bacteria obtained from nature, includingBacillus, Aeromonas , Rhizobium  and Streptomyces , have been shown to synthesis of melanin using the copper-containing enzyme tyrosinase (monophenol monooxygenase EC 1.14.18.1) (Wang et al., 2020). Bacterial melanin is produced by the usage of the enzyme tyrosinase, which oxidises into L-tyrosine and then converts to L-3, 4-dihydroxyphenylalanine. Finally, the transformed melanin synthesis takes place through the oxidoreduction process with a colour range of black to brown (Velmurugan et al., 2020). Melanin is the most stable, soluble, biochemically resistant, negatively charged, hydrophobic, high molecular weight, amorphous substance, but it is insoluble in common organic solvents, aqueous acid and water. There are three types of melanin based on colour and structural classes: (i) eumelanins (ii) pheomelanins (iii) allomelanins are colour pigments that range from black to brown in colour and that are synthesised via the standard. Pheomelanins are brown, red or yellow coloured pigments which are produced in the course of oxidation of tyrosine and/or phenylalanine to dihydroxyphenylalanine (DOPA) and dopaquinone. Pheomelanin results from cysteinylation of DOPA and these are sulphur-containing compounds. Allomelanins include nitrogen-free heterogeneous groups of polymers formed from catechol precursors. They are found in microorganisms and plants, whereas eumelanins and pheomelanins are found in animals only (Tarangini & Mishra, 2013). Microorganisms used melanin to protect themselves from heat, chemical (heavy metals and oxidising agents), enzymatic lysis, alveolar macrophages. There is a wide range of applications by using melanin in the fields of antimicrobial, antiviral, anticancer, antioxidant and anti-inflammation assays. Melanin has a high absorbing capacity of electromagnetic radiation, viz., visible light, ultraviolet radiation, and X-rays because of this property, the pharmaceutical and cosmetic industries use it in huge amounts. It has the ability to bind heavy metals and radionuclides (Wang et al., 2020), Which is used in the recycling of heavy metal-contaminated waste water. The mass production of melanin pigment is in high demand due to its significant bioactive potential properties and capacity to be employed in a wide range of applications. Furthermore, marine biological organisms as a major source for the synthesis of melanin pigment is an intriguing choice for both researchers and industries for its increased number of characteristics, including being safe, easily degradable and eco-friendly without causing severe side effects (Elsayis et al., 2022).