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Articles by Mahmoud M. Berekaa
Total Records ( 3 ) for Mahmoud M. Berekaa
  Mahmoud M. Berekaa , Nadia A. Soliman and Yasser R. Abdel-Fattah
  In a molecular screening program to select a potent thermostable amylase from a previously isolated thermophiles, a locally isolated, thermophilic lipase-producing Geobacillus thermoleovorans YN (accession number AF385083), was shown to secrete a thermostable α-amylase constitutively. The optimal enzyme activity was measured at 75°C, where 90% of the activity was retained at 80°C after one hour of incubation. A catabolite repression due to the addition of glucose to the basal salt medium was demonstrated, while 4 folds increase in volumetric production was achieved in LB and starch-supplemented basal salt media and presented in SDS-PAGE and zymogram. A blunt end PCR fragment (2146 bp) was amplified from genomic DNA using a designed set of primers and ligated to Bluescript —II KS(+) vector, transformed to E. coli DH5-α competent cells by electroporation and screened on LB-agar plates induced with IPTG. Nucleotide sequencing of selected clone revealed two ORFs, the first was (GTG) with a molecular size 1649 nucleotides encoding 549aa residues of a predicted molecular weight 62.592 kD and the second (ATG) with a molecular size 1613 nucleotides encoding 537aa residues of a predicted molecular weight 61.04 kD.
  Mahmoud M. Berekaa
  A bacterium isolated from old tire sample in Alexandria, Egypt, was shown to be able to utilize natural rubber and other isoprenoide compounds as a sole source for carbon and energy. Taxonomic analysis of the strain based on morphological and physiological studies indicated that the bacterium belongs to nocardioform actinomycete Nocardia sp. strain-MBR. Degradation behavior as well as SEM examinations indicated that the strain grow adhesively and depends on direct contact with the rubber substrate so belongs to the CMN group. Semicontinuous degradation of NR granules resulted in approximately 7% increase in percent CO2 release during growth. Schiff`s reagent staining revealed that the bacterium showed a higher colonization efficiency on small and treated pieces of NR-latex gloves, while a lower colonization efficiency when grown on large and nontreated NR-latex gloves. Formation of bacterial films and occurrence of compounds containing aldehyde groups during cultivation was also confirmed. Degradation of synthetic rubbers as well as other acyclic isoprenoids and compounds of analogous structure namely, phytol, squalene, squalane and prostane was recognized indicating that the bacterium has the metabolic capability to utilize these compounds as sole carbon source.
  Mahmoud M. Berekaa , Yasser R. Abdel-Fattah , Samia M. El-Sayed , Aliaa M. EL Borai and Samy A. El Aassar
  An optimization study of biopolymer production by locally isolated Bacillus sp. strain-R was carried out, where analysis indicated that it is a polyamide homopolymer consists mainly of glutamate. Preliminary experiment to address the most suitable carbon and nitrogen sources revealed that a production of 14.25 g L-1 of the polyamide (polyglutamate) was achieved in the presence of glucose and ammonium sulfate. To evaluate the effect of different culture conditions on the production of PGA, Plackett-Burman factorial design was carried out. Ten variables were examined for their significance on PGA production. Among those variables K2HPO4, KH2PO4, (NH4)2SO4 and glucose were found to be the most significant variables that encourage PGA production. The pre-optimized medium showed approximately three folds increase in PGA production.
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