S. H. Omar

Alexandria University, Al Iskandarīyah, Alexandria, Egypt

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Publications (7)20.02 Total impact

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    ABSTRACT: Acetone fractionation of Bacillus lentus culture filtrate yielded the highest -amylase activity and the 66.6% fraction reached 13-fold that of the crude enzyme preparation. Gel filtration and ion exchange chromatography afforded a pure -amylase (relative molecular mass, 42 000). The pure enzyme was highly active on starch and dextrin. It produced a mixture of oligosaccharides as major products of starch hydrolysis. Maximal activity was reached at 70 C and pH 6.1. Ca2+, Na+, K+ and Sr2+ ions stabilized or slightly stimulated the enzyme whereas Ag+, Co2+, Hg2+, Zn2+, Cd2+ and Fe3+ ions strongly inhibited the activity. The enzyme contained 16 amino acids, of which aspartic and glutamic acids were present in the highest proportions.
    No preview · Article · Nov 1992 · Applied Microbiology and Biotechnology
  • Sanaa Hamdy Omar · Siegfried Honecker · Hans-Jürgen Rehm
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    ABSTRACT: The formation of citric acid, oxalic acid, erythritol and glycerol by three strains of Aspergillus niger immobilized in calcium alginate was investigated and compared with that of free cells when cultivated in shake flasks under phosphate limitation. Morphological changes were followed using an electron microscope. The production of acids and polyols, the consumption of glucose and fructose, and also the morphological changes were strain-dependent. The results also reflected the influence of long storage of a strain on productivity, morphological behaviour and phosphate consumption.
    No preview · Article · Dec 1991 · Applied Microbiology and Biotechnology
  • S. H. Omar · U.W. Büdecker · H.-J. Rehm
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    ABSTRACT: The degradation rate of hydrocarbons in oily sludge obtained from a flotation unit by free and immobilized cells in shaking flasks and in a stirred tank reactor was investigated. For the biodegration of 3.3% hydrocarbons free cells and cells immobilized on granular clay were used. Free cells needed 7–8 weeks to use 30% of the 3.3% hydrocarbons, whereas with immobilized cells the same result was obtained after 3–4 weeks only. In shaken flasks with high hydrocarbon concentrations (8%), immobilized Candida parapsilosis degraded 90% of the hydrocarbons in the oily sludge within 3 weeks, while free cells degraded only 27.5% in the same period. In degradation experiments with a bioreactor, free and immobilized cells of the isolate ISO-OS B 20 showed better results compared to cultures in shaken flasks due to better aeration and mixing. Free cells degraded 50% of the 5% hydrocarbon-containing oily sludge in 7 weeks, whereas immobilized cells gave the same result after only 4 weeks.
    No preview · Article · Oct 1990 · Applied Microbiology and Biotechnology
  • S. A. El-Aassar · S. H. Omar · H. -J. Rehm
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    ABSTRACT: Living cells of Candida parapsilosis KSh 21 were immobilized by adsorption on different types of glass rings. The presence of n-tetradecane enhanced the cell adsorption especially on normal glass rings. The high adhesion of cellulose-coated glass rings and of sintered glass rings induced a quick adsorption of the cells. The quantity of 1-tetradecanol produced in the cultures of immobilized cells especially on SGR was higher than that of the free cells. Low numbers of free cells released in the immobilized cultures were observed. Better contact between the immobilized cells and oil droplets was noticed.
    No preview · Article · Oct 1988 · Applied Microbiology and Biotechnology
  • S. H. Omar · H. -J. Rehm
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    ABSTRACT: The immobilization intensity of cells of Penicillium frequentans and Candida parapsilosis on materials such as granular clay, granular clay + aquifer sand and aquifer sand alone, was followed by scanning electron microscopy (SEM). The results demonstrate that the granular clay was the best adsorbent for both organisms, followed by the mixture of both granular clay and aquifer sand. Poor adhesion of cells was detected on using aquifer sand alone with C. parapsilosis. The highest degree of degradation of the alkane mixture (C12−C18) used was achieved by cells immobilized on granular clay, followed by those cells adsorbed on clay and sand. The weakest degradation was observed with cells immobilized on the sand alone.
    No preview · Article · Feb 1988 · Applied Microbiology and Biotechnology
  • S.H. Omar · H.J. Rehm
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    ABSTRACT: The study of the effect of different carbon sources reflected the following results: 1. Candida parapsilosis (wild type and mutant) could not utilize citrate and glyoxylate and could grow well on pyruvate, acetate and to some extent on α-ketoglutarate, trans-aconitate, isocitrate and succinate. 2. Cells grown on tetradecane and pentadecane formed much more pseudomycelium than cells grown on the other tested carbon sources. 3. The catalase activities of the cells grown on tetradecane were generally much higher than those of the cells grown on acetate or glucose. 4. The tetradecane-grown cells of both organisms contain more lipid than glucose-, acetate- or succinate-grown cells. 5. Among the fatty acids found in the cells, the even-numbered dominate. A few odd-numbered were detected. 6. Enzymes of the glyoxylate cycle had very high activities on acetate and tetradecane, but very low ones on glucose and succinate medium. The two strains had with all the carbon sources a high citrate synthase activity. 7. High concentrations of glucose (2.5% and more) repressed the enzyme activities tested while acetate abolished this effect. Many authors have reported the fermentative production of citric acid from hydrocarbons (Nakanishi et al. 1972; Puklowski et al. 1976; Schröder 1976), the effect of hydrocarbons on the morphology of n-alkane degrading yeasts (Hirai et al. 1972), the effect of substrate on the fatty acid composition of hydrocarbon utilizing microorganisms (Dunlap and Perry 1967; Mishina et al. 1973; Source on enzymes of the tricaboxylic acid- and glyoxylate cycle (Gosling and Duggan 1971; Lozinov et al. 1976; Kleber and Aurich 1973, 1974; Fritsche 1968; Nabeshina et al. 1977), and catalase activity of hydrocarbon metabolizing yeasts (Teranishi et al. 1974a, b). Each author used a different yeast strain and no work has reported these different physiological studies for one organism at a time. In a previous work we reported the effect of pH, temperature, age and trans-aconitate on growth and enzymes of Candida parapsilosis (Omar and Rehm 1980). The following paper deals with experiments on the utilization of various carbon sources and on the comparison of enzyme activities of the TCC and glyoxylate cycle, catalase and fatty acid composition of C. parapsilosis.
    No preview · Article · Mar 1980 · European Journal of Applied Microbiology and Biotechnology
  • Sanaa Hamdy Omar · H. J. Rehm
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    ABSTRACT: The activity of enzymes of the tricarboxylic acid (TAC) and glyoxylate (GC) cycles in Candida parapsilosis (wild type KSh 21 and mutant 337) were studied under different physiological and metabolic conditions. C. parapsilosis differed in most of its enzyme activities from other non-citric acid producing yeasts. Furthermore, pH-value, temperature and age of culture proved to act differently on both strains of the tested organism.The addition of trans-aconitate increased not only the growth but also the activities of citrate synthase and some other enzymes while that of aconitase decreased enormously.The high citrate synthase activity might be connected with the role of citrate in the transport of acetyl groups.
    No preview · Article · Feb 1980 · Applied Microbiology and Biotechnology

Publication Stats

85 Citations
20.02 Total Impact Points


  • 1992
    • Alexandria University
      • Department of Botany and Microbiology
      Al Iskandarīyah, Alexandria, Egypt
  • 1980-1991
    • University of Münster
      • Institute of Mineralogy
      Muenster, North Rhine-Westphalia, Germany