الفهرس 
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Abstract
The present study was carried out in department of Genetics, Centre of Agriculture Genetic Engineering, and Biotechnology (CAGEB), Faculty of Agriculture and Agriculture Research Centre in the period -#102;-#114;-#111;-#109; 2007 to 2011. br The avermectins, a family of new anthelmintic agents, were isolated -#102;-#114;-#111;-#109; the mycelia of Streptomyces avermitilis. Streptomyces avermitilis is a soil bacterium produce that carries out the production of secondary metabolites, avermectin, is commercially important in human and veterinary medicine the avermectins. Avermectins are the active components of some insicticidal and nematocidal products used in agriculture, it also have killing ability to plant parasite nematode, so the bioassay method used to determine and compare the S. avermitilis culture filtrate killing ability. br The goal of the present work: br • How to obtain and maintain the avermectin producing strain S. avermitilis NRRL 8165. br • Induction of mutation using ethedium bromide to improve the productivity and killing ability of S. avermitilis to plant parasite nematodes. The point is that ethedium bromide could interfere with nucleic acids synthesis that results in replication inhibition and causes framshift mutations in bacteria. br • The parent strain S. avermitilis as well as its mutants were identified morphologically and assayed chromatograpically by TLC and bioassay on plant parasite nematodes. br • br The important results of this study could be summarized as follows: br • Morphological and physiological properties of the strain were determined on different growth medium and by assaying the production of different enzymes. br • Bioassay of avermectin production in S. avermitilis culture filtrate and its killing ability was done on plant parasite nematode larvae, indicating that it has a great killing ability reaching to 99% after five days. br • Another chromatographic assay was done by TLC to improve the production of avermectin in S. avermitilis culture filtrates. br • Avermectin production was improved by introducing mutation in Streptomyces avermitilis NRRL 8165 using different concentrations (25, 50, 75, 100 and 125µg/ml) of ethedium bromide (5g/ml). br • Improvement of killing ability of S. avermitilis NRRL 8165 was occurred by introducing mutation in it using ethedium bromide as a mutagen, we obtained more than 100 different mutants and isolated about 65 mutants with different shape, color, sporulation density and pigmentation color which range -#102;-#114;-#111;-#109; dark brown to yellow and orange. br • Mutant named MC4R51 was more efficient than parental strain in avermectin production when assayed for killing ability on plant parasite nematode larvae -#119;-#104;-#101;-#114;-#101; in the number of survive larvae were 0.0 -#102;-#114;-#111;-#109; the beginning 2000 larvae after 12days compared with the survive larvae of parental strain in the same period of culture filtrate exposure 18 larvae. br • Biochemical assay using SDS-PAGE electrophoresis and chromatographic assay using TLC also occur to the mutants as well as parental wild type S. avermitilis NRRL 8165. br -#102;-#114;-#111;-#109; all the above results we concluded that Streptomyces avermitilis could be maintained and produced avermectin using simple synthetic and natural media. Avermectin production within the culture filtrate of S. avermitilis could be assayed using both bioassay (using avermectin killing ability to nematode larvae) and chromatographic methods (using both TLC). Induction of mutation by ethedium bromide produced new mutant strains that have more killing ability than the parental wild type.