Isolation and Molecular Identification of Streptomyces spp. with Antibacterial Activity from KSA

Introduction: The genus Streptomyces represents a group of microorganisms that are widely distributed in nature. The genus Streptomyces, filamentous soil bacteria, has been described as the greatest source of the commercially available antibiotics. Streptomyces are also reported to produce other valuable bioactive secondary metabolites acting as antitumor agents, immune-osuppressive agents, and enzymes. In this study, a wide survey was conducted across Saudi Arabia.  Soil samples were collected from different governorates representing different climatic conditions.
Methods: The soil sample was collected randomly from the agricultural lands in Riyadh and Qassim in Saudi Arabia. All the samples were pre-treated with calcium carbonate to reduce the number of vegetative bacterial cells, while allowing many Actinomycetes spores to survive. The collected samples were isolated by serial dilution method and identified based on cultural, morphological, microscopic, biochemical, and sequence analysis of 16S RNA gene parameters. The collected samples were analyzed for antimicrobial activities by perpendicular streak and disc diffusion methods, against the Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis), Gram-negative Escherichia. coli, Enterococcus aerogenes,  and filamentous fungi  Candida albicans .
Results: Analysis of morphological and biochemical characteristics and the 16S rDNA gene sequence indicated that all  selected isolates belonged to the genus Streptomyces. Moreover, screening of the isolates with regard to their antimicrobial activity against indicator bacteria, the optimum growth and antimicrobial compound production  was found to be a maximal pH 8, in the shaker incubator at 28ºC, for a period of 10 days.
Conclusions: The S. flavogriseus showed a broad spectrum of antimicrobial activities against the test organisms and this opened further research investigations on purification and structural characterization of the active compounds from the crude extract