Avaliação da produção de melanina por Streptomyces sp. isolado do manguezal

Abstract

Melanin is a biopolymer, generally dark in color, present in virtually all living things such as animals, plants, and microorganisms. This pigment presents high antioxidant capacity and UV rays absorption. Due to these properties, it has several applications in the pharmaceutical, food, cosmetics, biomaterials, and agricultural industries. This pigment can be extracted from a microbiological source and is found in various environments, including mangroves. The mangrove swamp is a transitional ecosystem between marine, terrestrial, and freshwater environments, creating a highly unique environment that is prone to serve as a source of microbiological diversity and microbial metabolites. With this in mind, the present work aimed at the isolation of melanin-producing microorganisms from a mangrove sediment sample, as well as the production of the pigment and its characterization by spectroscopy techniques. Two different culture media were used for the isolation of the mangrove microorganisms and a medium containing tyrosine for the identification of melanin production. Four isolates were selected for an initial screening in liquid medium evaluated for melanin production and the one that presented the highest amount of the purified biopolymer was identified by 16S rRNA gene sequencing and its phylogenetic tree was built. The culture medium was evaluated through a 24-1 factorial design by varying the composition of: corn starch, soy peptone, yeast extract and tyrosine and the effects that these variables had on melanin production was evaluated. The pigment obtained was purified by the acid hydrolysis method and analyzed by UV-Vis spectrophotometer and FTIR. In all, 75 isolates from the mangrove were obtained and 12 showed production of dark pigment similar to melanin. Among the four microorganisms tested for melanin production, isolate MG08 was chosen as a model organism and identified as Streptomyces sp. After analyzing the results of the statistical planning, it was identified that only soy peptone had a significant effect on melanin production. The isolate MG08 produced a maximum of 11.18 g.L-1 of melanin. Therefore, the concentrations of the medium components were defined as (g.L-1): corn starch, 2.0; soy peptone, 20.0; yeast extract, 12.5; L-tyrosine, 1.0; magnesium sulfate, 0.5; calcium chloride, 0.1; sodium chloride, 5.0; copper sulfate, 0.05; iron sulfate, 0.05; pH 6.5, temperature 28 °C, agitation 150 rpm for 7 days. Through the spectroscopy techniques performed, the pigment obtained was classified as eumelanin. Therefore, it was concluded that the mangrove soil sample used was able to provide a large amount of melanin-producing microorganisms.