Purification and structure elucidation of antifungal and antibacterial activities of newly isolated Streptomyces sp. strain US80

A new actinomycete strain, designated US80 and producing antimicrobial activities against Gram-positive and Gram-negative bacteria and fungi, was isolated from Tunisian oasis soil. Cultural characteristic studies strongly suggested that this strain belongs to the genus Streptomyces. The nucleotide sequence of the 16S rRNA gene (1517 pb) of Streptomyces sp. strain US80 exhibited close similarity (97-98%) with other Streptomyces 16S rRNA genes. Similarity of 98% was obtained with the 16S rRNA gene of Streptomyces roseoflavus, which produces the aminoglycoside antibiotic flavomycin. Study of the influence of different nutritional compounds on production of bioactive molecules showed that the highest antimicrobial activities were obtained when glucose at 1% (w/v) was used as sole carbon source in the presence of magnesium. Extraction of fermentation broth of Streptomyces sp. strain US80 and various separation and purification steps led to isolation of three pure active molecules. The chemical structure of these three compounds, named irumamycin (1a), X-14952B (1b) and 17-hydroxy-venturicidin A (1c), was established on the basis on their IR, ESI-MS, 1H and 13C/APT NMR data and by comparison with reference data from the literature.