A NEW Streptomyces STRAIN AHA8 FROM DESERT SOIL: ISOLATION, TAXONOMIC IDENTIFICATION, AND ANTAGONISTIC PROPERTIES

Abstract

Actinobacteria from extreme environments represent a valuable source of novel bioactive secondary metabolites with potential antimicrobial applications. The aim of this study was to isolate, identify, and evaluate the antimicrobial potential of a newly isolated strain of actinobacteria. AHA8 strain, was isolated from an Algerian desert soil sample in the Ahaggar region (Tamanrasset) by the dilution-agar plating method using a chitin-vitamins B medium supplemented with nalidixic acid and actidione. Morphological characterization indicated that this strain belonged to the genus Streptomyces. Phylogenetic analysis based on the 16S rRNA gene showed that the strain is closely related to Streptomyces djakartensis NBRC 15409T (99.57% sequence similarity). Strain AHA8 showed very strong activity against pathogenic staphylococci, including Staphylococcus aureus (MRSA 639c), as well as against other Gram-positive bacteria: Bacillus subtilis (ATCC 663) and Listeria monocytogenes (ATCC 13932). Additionally, the strain exhibited a moderate activity against mycotoxigenic and phytopathogenic fungi, including Aspergillus carbonarius (M333), A. westerdijkiae (ATCC 3174), Fusarium culmorum (Fc), and Umbelopsis ramanniana (NRRL 1829). Almost the same results were observed for Gram-negative bacteria and the pathogenic yeast Candida albicans (M3). Therefore, four solvents (n-hexane, dichloromethane, ethyl acetate, and n-butanol) were used to extract the bioactive secondary metabolites produced by the AHA8 culture on a synthetic starch medium. The highest antibacterial activity was obtained with the butanolic and ethyl acetate extracts. These findings demonstrate that the desert-derived strain AHA8 represents a promising source of antimicrobial secondary metabolites and supports further studies aimed at the purification and characterization of its bioactive compounds.