Properties, various functions and application of bacterial melanins – some properties and possible application of melanin produced by Azotobacter chroococcum

Abstract

Melanins are a group of macromolecular pigments formed as a result of oxidative polymerization of phenolic and indole compounds. They are considered the most common, heterogeneous, resistant and evolutionarily oldest pigments found in nature. Melanins occurrred very early in the evolution of various groups of organisms. They have already been found in dinosaur, bird and primitive cephalopod fossils. Today, melanins are found in every kingdom of living organisms and play an important role in the processes of reproduction, thermoregulation, chemoprotection and camouflage. In addition to the important functions they perform in organisms, they exhibit a different chemical structure and are characterized by a wide range of colors, from black-brown to yellow-red. Differences in chemical structure have become the criterion for dividing melanins into four groups, i.e. eumelanin, allomelanin, pheomelanin and neuromelanin. Production of melanins is characteristic for many microorganisms, including free-living Azotobacter bacteria. The genus Azotobacter comprises eight species and only Azotobacter bryophylli does not produce pigments. Azotobacter chroococcum, the most abundant in soils all over the world, produces a dark brown melanin pigment non-diffusible into the substrate. Melanins synthesized by this species of bacteria increased the growth of some plants and detoxification of soils and waters polluted with heavy metals. In addition, the method of obtaining melanin produced by A. chroococcum is simple and relatively cheap compared to the cost of obtaining synthetic melanins, which gives the opportunity to conduct further research on the use of this pigment in biotechnology and molecular biology. In work it was describe the physicochemical properties, various functions and possible applications of bacterial melanins in various industries. The publication also summarizes the current knowledge on some properties and the possibility of use in bioremediation of soils and waters contaminated with heavy metals melanins synthesized by Azotobacter chroococcum.