Otimização da produção de melanina por linhagens recombinantes de Escherichia coli

Abstract

Melanin is a biological pigment responsible for the coloration of the skin, hair, and eyes in humans and many other organisms. It has numerous biotechnological applications in medicine, pharmaceuticals, environmental technologies, and nanotechnology, owing to its antioxidant properties, its use as a natural colorant, and its potential for the bioremediation of heavy metals. Several microorganisms are capable of producing different types of melanin, and recombinant strains have recently been developed to improve the production of this valuable bioproduct. In this context, the present study proposed the cloning of the Bacillus thuringiensis tyrosinase gene (melBt) into different Escherichia coli strains for melanin production from tyrosine. In addition, several process parameters were evaluated, including the carbon source (with glycerol supplementation enabling the production of up to 2 g/L of melanin), medium supplementation with tyrosine, which resulted in a threefold increase in the final melanin concentration compared with unsupplemented cultures, induction conditions, and additional genetic modifications. These modifications included the expression of genes involved in oxygen uptake (vhb50) and the aromatic biosynthetic pathway (tktA, aroE, and aroD), leading to a substantial increase in melanin production compared with strains lacking these genetic targets. The engineered strains were cultivated in triplicate in baffled shake flasks containing LB medium with or without supplementation under orbital agitation. The results demonstrated a strong influence of the E. coli host strain on melanin production, as well as significant effects of the carbon source and the presence of tyrosine in the culture medium. Furthermore, all of the additional genes evaluated positively affected melanin biosynthesis, allowing the engineered strains to outperform several previously reported microbial melanin production systems. Overall, this work resulted in the development of promising recombinant strains for melanin production and provided important initial insights for further optimization of the production process for this biotechnologically relevant compound.