Résumé:
In the interest of discovering new antibiotic molecules, the antibacterial activity of ten fungal species of Aspergillus genus isolated from soils taken from particular ecosystems (Laghouat and Teleghma) was sought against six bacterial strains; three with Gram + staining and three with Gram - staining. The results of the demonstration by different techniques (cylinders, disks and wells) have allowed us to select for the rest of our work three fungal species (A. quadrilineatus, A. niveus and A. wentii) that have a considerable antibacterial effect, and which are not well developed by researchers in the field of secondary metabolites with antibacterial activity. In order to optimize the extraction conditions of the bioactive molecules of these strains, five solvents in different polarities were tested, of which chloroform turned out to be the best one. After the selection of this solvent, four culture media of various compositions were used to determine the most adequate medium for the production of antibacterial substances. The results show that the nature of the components of these media (carbon source, nitrogen, and mineral source) greatly influences the production capacity of antibiotics in fungi. Moreover, the study of the stability of bioactive molecules reveals that the majority of active extracts maintain their activity after heat treatment (up to 100 °C) and exposure to light. In addition, the separation of antibacterial molecules by chromatographic techniques allowed us to select an active fraction. After the analysis of this fraction by UPLCMS, 24 peaks corresponding to 24 molecules were revealed with determination of their chemical characteristics: m/z ratios, formulas, retention time and intensities.
