Microbial cell factories for melanin production: progress and opportunities for industrial production

Melanins are ubiquitous pigments distributed throughout the biosphere in different forms and structures based on the substrate (phenolic and indolic) from which they are derived. Melanins are predominantly black/brown and sometimes melanins of color yellow/red have also been observed. Though melanins are widespread, at present their applications are only limited because commercially available melanins are often made through the synthetic process which impedes their application due to poor sensitivity. Melanins from biological sources are of great interest because of their biocompatibility and availability in microbes, especially bacteria. Owing to its rising demand, bacterial melanin can be easily produced and optimized in mass by proper fermentation conditions or by overexpressing the genes encoding enzymes such as polyketide synthase, tyrosinase, and laccase responsible for melanin production cost-effectively. Melanins are produced as a secondary metabolite in bacteria which aids in their survival under stressful environments. Besides providing pigmentation to the cells, many other biological properties, types, and potential applications of melanin in the fields of the textile, food industry, nanotechnology, and biomedical and the research gap that needs to be filled in previous discoveries for better application of melanin has been discussed in this review.