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Abstract -69- SUMMARY Actinomycetes espeoially members of the genus streptomyces produoe several valuable biologioally active substances such as enzymes, vitamins growth stimulators, pigments, toxins and antibiotics. Antibiotics are very important for plant, human, animals, poultry as therapeutic agents against different kinds of diseases. Therefore, this study was carried out to search for streptomyces isolate from the Egyptian soils, potent in the antibiotics production. Then studying the different factors affecting the antibiotics production. The results of the study could be summarized aa follow : 1. In this investi, gation 890 streptomyces isolates were obtaind from samples oolleoted from different areas in Egypt, namely EI-Kalubia, El-Sharkia, El-Dakahlia, EI-Beheira, Kafer El-Shaikh and Demyatta governorates. These isolates were purified on staroh nitrate agar then maintained on the o same medium at 4-5 C . 2. Soreen1Jlg of streptomyces isolates was made according to their antibiotio activity against the following test organisms : Staphylococcus aur,us, Klebsiella pneumonia, Bacillus, cereus. Salmonella typh1murium. Sarcina lutea, Escheriohia co11 and Candida Mbicans. -70- Seventy one strains of streptomyces were selected which produced antibiotic substances, and clearly inhibited the growth of the test organisms. Finally, these strains were compared with each other to determine the most antibiotic producer. Two strains namely Streptomyces~. (818) and Streptomyces~. (813) were selected as the highest producer of the a.ntibiotics among the other investigated strains. ’fwo organisms namely xi , Imewnonia and !!. cereus were selected, among the other investigated test organisms, which were the most sensitive to antibiotic substances produced by StreptoffiYcas~. (818) and Streptomyces ~. (873). Modified nutrient agar medium was selected as the medium of choice for carrying out the sensitivity teat siBce it gave the best growth of the test organisms. Selection of the fermentation medium :- -------------------~-~------------- ~’ive media na.ely wheat straw infusioll, wheat bran infusion,corn starch nitrate, rice bran infusion and Barseem straw infua10n were investigated for the antibiotic production bi streIfOmyC8s~. (818) and StreptOmYces ~. (873) to select the most suitable one. Wheat bran Lnfus10n was fou.nd to be toe best medium for the antibiotic productiOA. So, ’this ••••. um was selected to be used i.D the following experimea~s. _._~~-- -71- 5. ~he sensi~1vity test was carried out by the cup method and the disc method. No great differences were found between the results obtained by the two methods. So the disc method was used in the following experiments because it is easier to perform. 6- Results also showed that the most suitable concentration of agar in the medium used for testing the sensitivity of the test organisms towards the produced intibiotics was 9-12 gram agar/litre of the medium. This level of agar permitted more diffusion of the antibiotic which caused wider inbibiotion zone. 1- The optimum temperature for the antibiotic produ.ction by o Streptomyces ~. (818) was 26 0, while that for Streptomyces o ~. (813) was 31 C. 8. The optimwn pH for tbe antibiotic production was found to be ~ for both the two strains of streptomyces. 9. The optimum fermentation period for the antibiotic production by an.y of the 1wo Streptom.yces strains was found to be 9 days. -72- 10. Different carbon sources namely starch. glycerol. maltose, lactose, fructose, sucrose. substituted glucose in wheat bran infusion medium (control). Results showed that starch was the best carbon source in increasing the antibiotic production by Streptomyces ~. (818) and Streptomyces ~. (87.3). 11. The most suitable concentration of starch for antibiotic production in the fermentation medium was 8 gm/L. for Streptomyces~. (818) and 10 emiL for Streptomyces ~. (87.3) • ll. Different nitrog,en sources namely ammonium sulphate, LAsparagine, potassium nitrate, ammonium chloride, magnesium nitrate and urea substituted peptone in the wheat bran infusion medium. itesults showed that L-asparagine was 8Uperior to peptone in increasing the antibiotic. 13. The concentration of L-asparag1nlwhich produced the greatest amount of the antibiotic was found to be 5 gram of LAsparaginel L ot the aedium. 14. The antibiotic production at all optimum condi tiona was higher than any of -.ae other treatments this was found with both the two strept-.yces strains. --~-- -_._-------------- |