Studies on the Antimicrobial Activity of Streptomyces sp. Isolated from Jazan

Antimicrobial activity of streptomyces sp. (j12) isolatedfrom soil sample collected from jazan was studied. the isolate wasclassified according to the color of its mature sporulated aerialmycelia. it showed antimicrobial activities on solid and liquid mediaagainst some gram positive (bacillus subtilis and staphylococcusaureus), gram negative bacteria (escherichia coli and salmonellatyphi), as well as fungi (fusarium oxysporum f. sp. melongenae,rhizoctonia solani and candida albicans). results showed that oatmeal, starch casein and sabouraud media improved antibiotic biosynthesismore than yeast malt extract medium. biosynthesis of antibioticsby the species under agitated culture conditions was decreased.the influence of different cultural conditions on antibiotic biosynthesisby streptomyces j12 was studied. it showed that the highestantimicrob-ial activities were obtained after 6 days of growth at ph 7.2and a medium composition of 10g/l starch as the sole carbon source,2.5g/l of potassium nitrate as a nitrogen source and 0.3g/l casein.