Exploitation et caractérisation des substances bioactives sécrétées par une souche d’Aspergillus sp.

Abstract

The present work aims to evaluate some biological activities of a strain of spergillus and to identify its bioactive molecules potentially interesting. The exploration of corn samples destined to poultry feed allowed the isolation of 155 fungal strains belonging to the genus Aspergillus. One strain was selected, in vitro, by agar diffusion method, for its strong antimicrobial activity. Morphological and molecular identification of the selected isolate showed that it is Aspergillus creber. Preliminary test of the production of bioactive substances on different submerged culture media revealed that the Czapeck Yeast Broth (CYB) medium is the most favourable medium for this production. After the production of these molecules, the extraction was carried out using ethyl acetate. Study of the antimicrobial activity of ethyl acetate extract has shown that A. creber has a high activity against Candida albicans, with an MIC value of 0.325 mg / mL, followed by the multiresistant Gram-positive bacteria Staphylococcus aureus producing β-lactamase and Staphtloccoccus epidermidis resistant to methicillin with an MIC value of 0.625 mg / mL. Gram-negative bacteria were found to be more resistant with an MIC value ranging from 2.5 to 5 mg / mL. In addition, A. creber extract showed a significant capacity to trap free radicals DPPH • and ABTS • + with IC50 values of 108.76 ± 1.02 μg / mL and 90.82 ± 0.61 μg / mL respectively. A. creber extract showed also a powerful reducing power. The determination of total polyphenols by the FolinCiocalteu method showed a significant content of polyphenolic compounds estimated at 85.76 mg EGA / g. It is important to emphasize, that this work is the first one to have shown the ability of A. creber to produce molecules with antimicrobial and antioxidant activities. The chromatographic analysis of A. creber extract by ultra high performance liquid chromatography coupled with high resolution mass spectrometry (UHPLC-HRMS / MS) allowed the identification of five known molecules as asperlactone, emodin, sterigmatocystin, deoxybrevianamide E and norsolorinic acid, in addition to five other molecules which seem to be close to the known molecules but with some differences demonstrated in this work. Thus, it is probably that are novel molecules. To our knowledge, the demonstration of the production of asperlactone by A. creber, is a first, no study has mentioned the ability of the species of Aspergillus section Versicolores, in particular A. creber, to produce this compound. These results are promising and are considered to be a remarkable advance in the research of natural bioactive substances.