Isolation, Characterization and Antimicrobial Activities of Actinomycetes Isolated from a Tunisian Saline Wetland

Abstract

The " Sebkha of Monastir " is a Tunisian permanent wetland that constitutes a virgin environment to search new biotechnologically relevant microorganisms and activities. A total of 71 different strains were isolated, including 54 Streptomyces, 2 Micromonospora, 2 Nocardia, 4 Pseudonocardia and 9 non-streptomyces actinomyetes. Interesting antimicrobial activities were detected in liquid and solid cultures. The antimicrobial profiles depended upon the culture medium and/or the organic extraction. Several bioactive compounds were identified by liquid chromatography (LC) combined with mass spectrometry (MS) and then analyzed by MEDINA´s database and the Dictionary of Natural Products Chapman & Hall. Isoflavones (genistein and deidzein) are the most produced known active compounds. The chemical structures of four putative novel compounds were elucidated. Interestingly, unknown compounds produced by two strains (A8 and A11) actives against Gram negative bacteria were selected for further analysis on a large-scale. 16S rDNA sequencing allowed us to classify some active isolates as members of the Streptomyces and Micromonospora genera. All these findings prove the high antimicrobial activity of the actinomycetes strains isolated from the " Sebkha of Monastir " . The potential of this and other relatively unexplored extreme environments constitute a source of new biologically active secondary metabolites.