Antioxidant, antimicrobial and cytotoxic activities of secondary metabolites from Streptomyces sp. isolated of the Amazon-Brazil region

Bacteria of Streptomyces genus are a promising source of biologically active products, with applications in medicine, industry and agriculture. Therefore, the objective of this work was to evaluate the cytotoxic, antioxidant and antimicrobial activities of fermented rice extract and their semipurified fractions from Streptomyces spp. isolated of the rhizosphere of Paullinia cupana, Amazon-Brazil. For this, a bioguided study was carried out by the cytotoxic activity with methanolic extract of Streptomyces sp. ACTMS-12H UFPEDA 3405 (EMeOH-12H) partitioned with n-hexane, ethyl acetate and 2-butanol. The antioxidant activity was analyzed using the DPPH, ABTS and phosphomolybdenum methods, while the antimicrobial activity was investigated by microdilution method to determine the minimum inhibitory concentration (MIC) against species of bacteria and yeast. In the cytotoxicity test, the butanolic phase (FbuOH-12H) presented IC50 of 1.1 µg/mL against MOLT-4, with cell death probably by apoptosis, but did not cause cytotoxicity on peripheral blood mononuclear cell (PBMC) or human erythrocytes. Chemical prospecting detected the presence of saponins and reducing sugars on 2-butanol fraction (FBuOH-12H), which can be related to cytotoxicity. On the antioxidant activity by ABTS, the partition with ethyl acetate (FAcOEt-12H) showed antioxidant capacity of 1161.7 ± 0.04 µM of Trolox/g of extract, indicating an expressive reactivity of the phase with this radical. The aqueous phases (from hexane, ethyl acetate and methanol extracts) were active in all tested microorganisms, except E. faecalis.