CULTURAL CONDITIONS AFFECTING ANTIBIOTIC PRODUCTION BY STREPTOMYCES SPECIES
A total of 106 actinomycetes isolated from the rhizosphere of plants in abbatoir and refuse dumps in Awka and Onitsha were investigated for the production of antimicrobial substances. Five of them were found to show antimicrobial activity against Gram positive and Gram negative bacteria as well as fungi on solid media. Three of the very active isolates designated MP-75, SP -76 and QP-100 were further investigated in submerged medium in a shake-flask experiment using glucose and soy bean as carbon and nitrogen sources respectively. Isolates MP-75 and SP-76 were found to produce antimicrobial substances. The antimicrobial substance produced by isolates SP-76 showed the highest antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Klebsiella sp, Staphylococcus aureus and Bacillus sp. The isolates were identified as Streptomyces species based on their characteristic features. Activity of the antimicrobial substance produced by Streptomyces SP-76 was maximum when 4% (w/v) glucose and 2% (w/v) soybean were used in the fermentation process. Influence of surfactants on accumulation of antimicrobial substance by Streptomyces SP-76 in the fermentation broth showed that Tween 80, oleic acid, palmitic acid and stearic acid enhanced antimicrobial activity. The effect of growth promoters on antibiotic production by Streptomyces SP-76 indicated that peptone, casein and yeast extract stimulated antimicrobial activity against the test organisms. The effect of varying pH on antibiotic production by Streptomyces SP-76 showed that there was maximum antimicrobial activity at pH 7. In a time course for antibiotic production, maximum antimicrobial activity was obtained at 120h. Paper chromatography of the culture filtrate of Streptomyces SP-76 indicated that it contains more than one antimicrobial substance. From this, it can be seen that the growth and subsequent production of bioactive metabolites by Streptomyces SP-76 isolated from the soil.