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    Cadmium biosorption by Bacillus circulans strain EB1
    (Springer, 2005) Yilmaz, EI; Ensari, NY
    A heavy metal resistant bacterium, Bacillus circulans strain EB1 showed a high cadmium biosorption capacity coupled with a high tolerance to this metal when grown in its presence. Bacillus circulans EB1 cells grown in the presence of 28.1 mg cadmium/l were capable of removing cadmium with a specific biosorption capacity of 5.8 mg Cd/g dry wt biomass in the first 8 h. When the cells were pre-conditioned with low concentrations of cadmium in pre-grown medium, the uptake was increased to 6.7 mg Cd/g dry wt biomass. The maximum uptake of cadmium was during mid-logarithmic phase of growth. The resting cells (both wet and dry) of EB1 were also able to biosorb cadmium. Specific biosorption capacities of wet and dry biomass were 9.8 and 26.5 mg Cd/g dry wt biomass, respectively. Maximum cadmium removals by both wet and dry cells were at pH 7.0. The results showed that the cadmium removal capacity of resting cells was markedly higher than that of growing cells. Since both growing and resting cells had a high biosorption capacity for cadmium, EB1 cells could serve as an excellent biosorbent for removal of cadmium from natural environments.
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    Cloning and expression of the Clostridium thermocellum L-lactate dehydrogenase gene in Escherichia coli and enzyme characterization
    (Canadian Science Publishing, Nrc Research Press, 2004) Özkan, M; Yilmaz, EI; Lynd, LR; Özcengiz, G
    The structural gene for L-lactate dehydrogenase (LDH) (EC.1.1.1.27) from Clostridium thermocellum 27405 was cloned in Escherichia coli by screening the Lambda Zap 11 phage library of C. thermocellum genomic DNA. In one positive clone, an open reading frame of 948 base pairs corresponded to C. thermocellum ldh gene encoding for the predicted 315-residue protein. The ldh gene was successfully expressed in E. coli FMJ39 (ldh mutant) under the lac promoter. The recombinant enzyme was partially purified from E. coli cell extracts and its kinetic properties were determined. Clostridium thermocellum LDH was shown to catalyze a highly reversible reaction and to be an allosteric enzyme that is activated by fructose-1,6-diphosphate (FDP). For pyruvate, partially purified LDH had K-m and V-max values of 7.3 mmol/L and 87 mumol/min, respectively, and in the presence of FDP, a 24-fold decrease in K-m and a 5.7-fold increase in V-max were recorded. The enzyme exhibited no marked catalytic activity for lactate in the absence of FDP, whereas K-m and V-max values were 59.5 mmol/L and 52 mumol/min, respectively, in its presence. The enzyme did not lose activity when incubated at 65degreesC for 5 min.
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    Cloning, characterization and heterologous expression of the aspartokinase and aspartate semialdehyde dehydrogenase genes of cephamycin C-producer Streptomyces clavuligerus
    (Elsevier Science Bv, 2004) Tunca, S; Yilmaz, EI; Piret, J; Liras, P; Özcengiz, G
    Carbon flow through the lysine branch of the aspartate biosynthetic pathway is a rate-limiting step in the formation of cephamycin C, a broad spectrum P-lactam antibiotic produced by Streptomyces clavuligerus. In this study, genes which encode the enzymes catalyzing the first two steps of the aspartate pathway, ask (aspartokinase) and asd (aspartate semialdehyde dehydrogenase), in S. clavuligerus NRRL 3585 were cloned and sequenced. Nucleotide sequencing and codon preference analysis revealed three complete open reading frames (ORFs). ORF2 starts within ORFI and terminates by utilizing the same stop codon as ORFI, an arrangement typical of many ask genes. ORF3 is located 2 nucleotides downstream of ORF1,2. Database comparisons with these proteins identified ORFI as the large (a) subunit of aspartokinase, ORF2 as the small (P) subunit of aspartokinase and ORF3 as the aspartate semialdehyde dehydrogenase. The cloned genes were functionally expressed in auxotrophic Escherichia coli strains, CGSC5074 (ask(-)) and E. coli CGSC5080 (asd(-)), the two enzymes were partially purified from E. coli cell extracts and their kinetic parameters were determined. The effects of end product amino acids and diaminopimelic acid on the activity of Ask and Asd enzymes were also described. (C) 2004 Elsevier SAS. All rights reserved.
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    DNA cleavage activity of diazonium salts
    (Scientific Technical Research Council Turkey, 2003) Kizil, M; Yilmaz, EI; Pirinççioglu, N; Aytekin, Ç
    4-Fenoldiazonium tetrafluoroborate and 4-benzoicaciddiazonium tetrafluoroborate was prepared and was shown to be an effective DNA cleavage agent in the presence of the 1-electron donor copper(II) chloride. Its mechanism involves the generation of the aryl radical cleaving DNA by hydrogen atom abstraction from deoxyribose sugar.
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    Metal tolerance and biosorption capacity of Bacillus circulans strain EB1
    (Elsevier Science Bv, 2003) Yilmaz, EI
    A heavy-metal-resistant bacterium Bacillus sp., strain EB1 was isolated from heavy-metal-contaminated soil in the southeast region of Turkey. Based on 16S ribosomal DNA sequencing, the microorganism was closely related to Bacillus circulans. Minimal inhibitory concentrations of metals (MICs) for the bacterium were determined. Bacillus EB1 exhibited high MIC values for metals and a large spectrum of antibiotic resistance. The order of toxicity of the metals to the bacterium was Cd = Co > Cu > Ni > Zn > Mn in solid media. The effects of increasing metal concentrations to the growth rate were determined in order to obtain precise patterns of resistance in liquid cultures. From the results of heavy metal toxicity, inhibitory concentrations in solid media were higher than those in liquid media. Metal biosorption was determined during the course of growth. B. circulans strain EB1 was capable of removing 90% of Mn, 68% of Zn, 65% of Cu, 45% of Ni and 40% of Co during the active growth cycle with a specific biosorption capacity of 25, 22, 20, 13 and 12 mg/l, respectively. Since Bacillus cells could grow in the presence of significant concentrations of metals and due to high metal biosorption capacity in aerobic conditions, this bacterium may be potentially applicable in in situ bioremediation of heavy-metal-contaminated aqueous systems. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.