Optimized production of antimicrobial compounds by endophytic Aspergillus niger CBMAI 2766

Fungi can adapt their metabolism to different cultivation conditions, which may accompany changes in secondary metabolites, but few cost-effective approaches were presented. Therefore, Aspergillus niger CBMAI 2766 was studied aiming at the obtention of antibacterial compounds using KBr, an innocuous and inexpensive salt. The addition of this salt to culture medium was an interesting strategy for obtention of natural products at higher concentrations, as observed by the increased extract mass that favored the isolation of biologically active compounds. Furthermore, an experimental design with temperature, pH, and KBr concentration was performed to maximize the obtained products. Seven compounds were isolated: the phenylalanine derivatives Aspernigrin A 1 and Pestalamide B 2, the polyketides RF-3192C 3, Foncesinone A 6 and Aurasperone A 7, and the bicoumarins Orlandin 4 and Kotanin 5. The bactericidal activity of 5 against Gram-positive bacteria was observed for the first time in this study. Furthermore, antimicrobial activities of the isolated metabolites 3-7 were described in the literature. In summary, the employed experimental design showed that 34 °C and 10g.L-1 KBr were optimal conditions for producing the bioactive compounds 5-7 employing this inexpensive salt as medium modifier. Thus, indicating that this proposal presents potential for enhancing antimicrobials production.