Produção de celulases e xilanases por actinobactérias isoladas do cerrado mineiro

Abstract

In general, the soil is one of the most diverse and heterogeneous habitats for Bacteria and Archaea in the planet. Among bacteria, Phylum Actinobacteria, consisting of micro-organisms Gram-positives, stands out for its wide biotechnological application, such as producing of bioactive compounds, including antibiotics, enzymes and several other metabolites of industrial interest. The Actinobacterias have been isolated in various biomass, all over the world. However, the Brazilian Cerrado, whose rich biodiversity is significant, has been poorly explored in the bioprospecting of actinobacterias species with potential biotechnological applications. Thus, this study aimed to isolate actinobacterias from Brazilian Cerrado soil during the season of high rainfall. A total of 1.432 actinobacterias strains were isolated in the municipalities, Arcos, Passos and Luminárias (Minas Gerais State, Brazil). The soils were characterised by chemical and microbiological analysis. The microbiological analysis led to the identification of nine genus (Streptomyces, Artrobacter, Rhodococcus, Amycolatopsis, Microbacterium, Frankia, Leifsonia, Nakamurella e Kitasatospora) and 92 distinct species in the season of high rainfall. The pH values of the soil samples from three regions varied from 4.1 to 5.5. There was not significant difference in the concentrations of phosphorus, magnesium and organic matter in the soils, among the studied areas. The samples from Arcos area showed large amounts of aluminum, which does not seem to have affected the actinobacterias populations found. The present data suggest that the number and diversity of actinobacterias species in tropical soils represent a vast resource, still little explored, for the production of bioactive compounds. The biotechnological application of actinobacterias identified was assessed as the ability of the isolated to produce enzymes of cellulolytic and xylanolytic complex. The strains isolated were evaluated in both seasons studied, high and low rainfall, being these last from another study, realized in the same sampling site. Preliminary semi-quantitative tests, made in Petri plates containing carboxymethylcellulose CMC and beech wood xylan as carbon sources, indicated, among the 92 species identified, 11 potential species producing enzymes, all belonging to the Streptomyces genus. The species were subsequently grown in the same substrates in submerged fermentation and analyzed for the enzymes production endoglucanase, β-glucosidase, endoxylanase and β-xylosidase. The best results were obtained in endoxylanase enzyme production by Streptomyces termitum. Subsequently, the strain was grown on lignocellulosic residues (bagasse and straw sugar cane and cocoa straw) in natura and pre-treated. The medium containing sugar cane bagasse in natura showed best results for the production of endoxylanase enzyme. An experimental model was then, proposed to optimize the production of the enzyme in said substrate, varying concentrations of sugar cane bagasse, yeast extract and pH from the medium culture. The results showed that the highest enzyme production (25.8 times higher) was when combining 2.75% sugar cane bagasse and 1.0 g/L of yeast extract to the medium culture alkaline (pH 9.7). From the results obtained may suggest the use of Streptomyces termitum species in biotechnological processes, due to production of endoxylanase in a medium culture simple and economical.