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Articles by S. Tork
Total Records ( 2 ) for S. Tork
  S. Tork , W.K. Hegazy , T.M.A. El-kawokgy and O.G.A. El-Gebaly
  The present study aimed to induce heat tolerant mutants in haploid Saccharomyces cerevisiae 5a FAIII strain by using different mutation methods. Three different mutation induction experiments were carried out to produce genetically stable heat tolerant Saccharomyces cerevisiae strains. The haploid strain 5a of the S. cerevisiae FAIII that has the highest growth rate was used throughout these experiments. Three thermo-tolerant mutants named as 5a1, 5a2 and 5a3 were obtained using N-methyl N-nitro N-nitrosoguanidine (MNNG), combination of ultra-violet radiation and hydroxylamine (UV+HA) treatments and spontaneous mutation, respectively. The mutants could tolerate 42 and 42.5°C but they couldn’t survive extended period of time at 43°C. The growth rate of the mutants indicated that they exhibited well growth at 42°C, while they exhibited slow growth rate at 42.5°C. Although (MNNG) induced thermotolerance mutation at high frequency, it was found that mutants induced following synergistic effect of (UV and HA) exhibited more stability. On the other hand, the spontaneous mutant exhibited the best growth rate at high temperature.
  S. Tork , M.M. Aly and L. Nawar
  This study aimed to isolate and identify a new local bacterial strain, able to completely degrade keratin-rich wastes into soluble and useful materials which can be used in many proposes. Bacterial keratinases are of particular interest because of their action on insoluble keratin substrates and generally on a broad range of protein substrates. These enzymes have been studied for de-hairing processes in the leather industry and hydrolysis of feather and keratin. Samples from poultry industry wastes, soil, water, fodder and feather were collected from different places in Jeddah, Saudi Arabia. Each sample was plated on feather meal agar plates containing 5 g L-1 feather as the sole carbon and nitrogen source and the obtained colonies were selected, purified and their growth were detected on skimmed milk agar and feather meal broth media. The well grown isolates on feather meal agar which producing the largest clearing zone on skimmed milk plate were selected for keratinase assays. Out of 23 bacterial isolates, 7 isolates were selected. The best keratinase producing bacterium kera MS21 was selected and identified based on morphological, physiological and some biochemical characteristics. It was recorded as a species belonging to the genus Pseudomonas and identified as Pseudomonas sp. The results of identification were confirmed by 16S rDNA studies. Precipitation and purification of the keratinase enzyme in addition to factors affecting enzyme activity were studied. The enzyme molecular weight was determined to be of 30 KDa using sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. The optimum temperature and pH were determined to be 37°C and pH 8.0, respectively. The effect of some proteases inhibitors and activators were also studied.
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