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In a screening program to study the antimicrobial activities of desert actinomycetes as potential producers of active metabolites, 75 actinomycete strains were isolated from the Egyptian desert habitats and tested. Out of the isolated 75 organisms, 32 (42.67%) showed activity against the used test organisms. The antimicrobial activities of the active desert actinomycete strains were classified into four groups according to their spectrum of activity on different groups of test organisms and it was found that 43.75% of the active isolates have activity against Gram-positive bacteria only, 28.13% have activity against both Gram-positive and Gram-negative bacteria, 15.63% have activity against Gram-positive bacteria and yeast, 12.50% have activity against Gram-positive, Gram-negative bacteria and yeast. The most potent actinomycete strain, designated D332, was selected for further studies including its identification and isolation of its active compound. Strain D332 was identified by studying its morphology, chemotaxonomy, biochemical characteristics and phylogenetic analysis of the 16S rRNA gene sequence. All phenotypic and genotypic characteristics were consistent with the classification of strain D332 to genus Streptomyces where it formed a distinct phyletic line in the Streptomyces 16S rRNA gene tree. On the other hand, the culture broth of strain D332 was extracted with ethyl acetate after fermentation for the production of the active compound then, the crude extract was partially purified by thin layer chromatography using a solvent system composed of heptane: ethyl acetate (3: 2). The results revealed that strain D332 produced one major compound active against Gram-positive and Gram-negative bacteria and yeasts.
Key words: Desert actinomycetes, antimicrobial activities, new Streptomyces strain, production of the active metabolite.