Abstract

The purpose of this study was to screen isolates of Streptomyces producing nonpolyenic antifungals. This choice was made to limit the problem of rediscovery of well-known antifungal families, especially polyenic antifungals. 68 Streptomycesstrains were isolated from the soil sample collected from Tunisian oases ecosystem. These strains were tested for their capacity to produce active compounds using the diffusion method against two bacteria: Escherichia coli ATCC 8739, Micrococcus luteus LB 14110; two filamentous fungi: Verticillium dahliae and Fusarium sp. and two yeasts: Candida tropicalis R2 CIP203 and Candida albicans ATCC 2019. Among these isolates, 40 strains (58.82%) showed antibacterial activity, 18 strains (26.47%) showed antifungal activity, while 12 strains (17.64%) exhibited a broad-spectrum activity against all tested indicator cells. The production of nonpolyenic antifungal metabolites by promising isolates was investigated using their antibacterial activity and ergosterol inhibition as well as the UV-vis spectra of their corresponding active extracts. The obtained results showed that 13 isolates (19.11%) produced nonpolyenic antifungal activity. These data indicate the richness of the Tunisian oases ecosystem in actinomycetes bacteria producing active compounds. This fact, may partly explain the resistance phenomena of the Tunisian oasis palms against some phyto-pathogen fungus such as Fusarium oxysporum sp. albidenis (bayoud).

Key words: Soil of Tunisian oases ecosystem, Streptomyces, nonpolyenic antifungal activity.