Characterization of Locally Isolated Streptomyces and their Potentialities as Sources of Novel Bioactive Compounds

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Nazik Mohamed Abdalla, Hammad
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University of Khartoum
Out of 175 only fifty five microorganisms isolated from different soil sample were studied morphologically and chemotaxonomically. According to the obtained results fifty two isolates were found to be Streptomyces sp. Whereas the remaining three isolates were identified as Nocardia sp. The isolates were evaluated for their production of secondary metabolites with biological activities. In order to enable preliminary screenings, the strains were cultivated on different culture media and screened for secondary metabolite production using HPLC. Out of the 55 extracts, 24 (44%) showed interesting unknown biologically active metabolites, 21 (39%) were found to contain known secondary metabolites, over 20 compounds were recognized as previously reported structures, and 9 (17%) were found to contain no metabolite of interest Among the 24 extracts which contain unknown secondary metaboites only 15 were tested for their biological activity using agar diffusion assay. The tested extracts vary in their effect against the both tested pathogenic microorganisms (Bacillus subtilis, Staphylococcus aureus, Escherichia coli , Pseudomonas flourescens ,Saccharomyces cerevisiae, Candida albicans and Botrytis cinerea)., 49% have shown activities against bacteria and fungi, 31% against bacteria alone, 13% against fungi alone and 7% have not shown activity against any of the tested organisms. According to the biological activity and HPLC analysis 15 isolates were selected for re-fermentation experiments. Two of the isolates IDU with the retention times of 11.4 and 11.9 and ID3i with the retention time 9.6 and 10 were selected for further investigation. The two isolates were scaled up using 10 and 20l fermentors using a pre-determined maximum production media. The time course of the secondary metabolite production was followed till the end of the fermentation period. After that the metabolites were harvested, isolated and purified using different chromatochraphy columns. Compounds U1 and U2 were isolated from IDU and the compounds A, B were isolated from the isolate ID3i. CAS assay test shows that all of the pure compounds isolated were siderophores. Antitumor test and biological activity shows that the compounds U1 and U2 have a strong effect against different human cell lines (gastric adenocarcinoma, hepatocellular carcinoma and breast carcinoma) and against pathogenic microorganisms. Structure elucidation shows that the two compounds U1 and U2 were a novel steromeric isomers of pyochelin, they are the first thiazolyl-type siderophores to be isolated from any Streptomyces strain any where in the world. They were produced naturally as stable methyl esters. The new compound, designated pyochelin reported here belongs to the pyochelin family, a group of compounds known for their iron chealeting propereties. Structure elucidation of combounds A and B indicated that these antibiotics are indolyl-oxazoles and they registered under the names SF 2583A and SF 2583B
233 Pages
Characterization ,Locally Isolated, Streptomyces ,Potentialities , Sources ,Novel Bioactive,Compounds;Characteristics of Streptomyces;Animal Kingdom