Production of destomycin-A antibiotic by Streptomyces sp. using rice straw as fermented substrate.

Hundred and twenty microbial isolates could be isolated from different soil samples collected from different localities in Egypt. One of the actinomycete culture AZ-H-A5 from three cultures was found to produce a wide spectrum antimicrobial agent when cultivated on rice straw. The actinomycete AZ-H-A5 could be isolated from a soil sample collected from Helwan district, Egypt. The nucleotide sequence of the 16s RNA gene (1.5 Kb) of the most potent strain evidenced an 85% similarity with Streptomyces pseudovenezue, EU841712 and Streptomyces galilaeus. From the taxonomic features, the actinomycetes isolate AZ-H-A5 matches with Streptomyces rimosus in the morphological, physiological and biochemical characters. Thus, it was given the suggested name Streptomyces rimosus, AZ-H-A5. The parameters controlling the biosynthetic process of antimicrobial agent formation including: inoculum size, different pH values, different temperatures, different incubation period, and different carbon and nitrogen sources, potassium nitrate, K2HPO4, MgSO4.7H2O and KCl concentrations were fully investigates. The active metabolite was extracted using ethyl acetate (1:1, v/v) at pH 7.0. The separation of the active ingredient and its purification was performed using both thin layer chromatography (TLC) and column chromatography (CC) techniques. The physicochemical characteristics of the purified antibiotic viz. color, melting point, solubility, elemental analysis, spectroscopic characteristics and chemical reactions have been investigated. This analysis indicates a suggested empirical formula of C20H37N13O13. The minimum inhibition concentrations "MICs" of the purified antimicrobial agent were also determined. The purified antimicrobial agent was suggestive of being belonging to Destomycin-A antibiotic produced by Streptomyces rimosus, AZ-H-A5.