Person: TOKSOY ÖNER, EBRU
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
TOKSOY ÖNER
First Name
EBRU
Name
72 results
Search Results
Now showing 1 - 10 of 72
Publication Metadata only Rheological characteristics of exopolysaccharides (EPSs) produced by Brevibacillus thermoruber(ELSEVIER SCIENCE BV, 2012) TOKSOY ÖNER, EBRU; Yildiz, Songul Yasar; Ozer, Tugba; Radchenkova, Nadia; Genc, Seval; Oner, Ebru Toksoy; Kambourova, MargaritaPublication Metadata only Purification, biochemical characterization and gene sequencing of a thermostable raw starch digesting alpha-amylase from Geobacillus thermoleovorans subsp stromboliensis subsp nov.(SPRINGER, 2011) KASAVİ, CEYDA; Finore, Ilaria; Kasavi, Ceyda; Poli, Annarita; Romano, Ida; Oner, Ebru Toksoy; Kirdar, Betul; Dipasquale, Laura; Nicolaus, Barbara; Lama, LiciaThis study reports the purification and biochemical characterization of a raw starch-digesting alpha-amylase from Geobacillus thermoleovorans subsp. stromboliensis subsp. nov. (strain Pizzo(T)). The molecular weight was estimated to be 58 kDa by SDS-PAGE. The enzyme was highly active over a wide range of pH from 4.0-10.0. The optimum temperature of the enzyme was 70A degrees C. It showed extreme thermostability in the presence of Ca2+, retaining 50% of its initial activity after 90 h at 70A degrees C. The enzyme efficiently hydrolyzed 20% (w/v) of raw starches, concentration normally used in starch industries. The alpha-amylase showed an high stability in presence of many organic solvents. In particular the residual activity was of 73% in presence of 15% (v/v) ethyl alcohol, which corresponds to ethanol yield in yeast fermentation process. By analyzing its complete amyA gene sequence (1,542 bp), the enzyme was proposed to be a new alpha-amylase.Publication Metadata only The Stimulatory Effect of Mannitol on Levan Biosynthesis: Lessons from Metabolic Systems Analysis of Halomonas smyrnensis AAD6(T)(WILEY, 2013) TOKSOY ÖNER, EBRU; Ates, Ozlem; Arga, Kazim Y.; Oner, Ebru ToksoyHalomonas smyrnensis AAD(T) is a halophilic, gram-negative bacterium that can efficiently produce levan from sucrose as carbon source via levansucrase activity. However, systems-based approaches are required to further enhance its metabolic performance for industrial application. As an important step toward this goal, the genome-scale metabolic network of Chromohalobacter salexigens DSM3043, which is considered a model organism for halophilic bacteria, has been reconstructed based on its genome annotation, physiological information, and biochemical information. In the present work, the genome-scale metabolic network of C. salexigens was recruited, and refined via integration of the available biochemical, physiological, and phenotypic features of H. smyrnensis AAD6(T). The generic metabolic model, which comprises 1,393 metabolites and 1,108 reactions, was then systematically analyzed in silico using constraints-based simulations. To elucidate the relationship between levan biosynthesis and other metabolic processes, an enzyme-graph representation of the metabolic network and a graph decomposition technique were employed. Using the concept of control effective fluxes, significant links between several metabolic processes and levan biosynthesis were estimated. The major finding was the elucidation of the stimulatory effect of mannitol on levan biosynthesis, which was further verified experimentally via supplementation of mannitol to the fermentation medium. The optimal concentration of 30 g/L mannitol supplemented to the 50 g/L sucrose-based medium resulted in a twofold increase in levan production in parallel with increased sucrose hydrolysis rate, accumulated extracellular glucose, and decreased fructose uptake rate. (c) 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1386-1397, 2013Publication Metadata only Improving the catalytic behaviors of Lactobacillus-derived fructansucrases by truncation strategies(ELSEVIER SCIENCE INC, 2021) TOKSOY ÖNER, EBRU; Ni, Dawei; Kirtel, Onur; Yin, Dejing; Xu, Wei; Chen, Qiuming; Oner, Ebru Toksoy; Mu, WanmengFructansucrases (FSs), including inulosucrase (IS) and levansucrase (LS), are the members of the Glycoside Hydrolase family 68 (GH68) enzymes. IS and LS catalyze the polymerization of the fructosyl moiety from sucrose to inulin- and levan-type fructans, respectively. Lactobacillus-derived FSs have relatively extended N- and Cterminal sequences. However, the functional roles of these sequences in their enzymatic properties and fructan biosynthesis remain largely unknown. Limosilactobacillus reuteri (basionym: Lactobacillus reuteri) 121 could produce both IS and LS, abbreviated as Lare121-IS and Lare121-LS, respectively. In this study, it was found that the terminal truncation displayed an obvious effect on their activities and the N-terminal truncated variants, Lare121-IS Delta 177-701 and Lare121-LS Delta 154-686, displayed the highest activities. Melting temperature (Tm) and the thermostability at 50 degrees C were measured to evaluate the stability of various truncated versions, revealing the different effects of N-terminal on the stability. The average molecular weight and polymerization degree of the fructans produced by different truncated variants did not change considerably, indicating that N-terminal truncation had low influence on fructan biosynthesis. In addition, it was found that N-terminal truncation could also improve the activity of other reported FSs from Lactobacillus species.Publication Metadata only Optimizing medium composition for TaqI endonuclease production by recombinant Escherichia coli cells using response surface methodology(ELSEVIER SCI LTD, 2005) TOKSOY ÖNER, EBRU; Nikerel, IE; Toksoy, E; Kirdar, B; Yildirim, RThe effect of medium composition on the TaqI endonuclease production, by recombinant Escherichia coli cells carrying a plasmid encoding TaqI endonuclease, was investigated using response surface methodology. The concentration of glucose, di-ammonium hydrogen phosphate, potassium di-hydrogen and magnesium sulphate in media were changed according to a central composite rotatable design consisting of 29 experiments and enzyme yields were determined. The results were fitted to a second order polynomial with an R-2 of 0.828. The model equation was then optimized using the Nelder-Mead simplex method to maximize enzyme yield within the experimental range studied. The optimum medium composition was found to be 6 g L-1 glucose, 1.5 g L-1 (NH4)(2)HPO4, 8 g L-1 KHPO4, and 0.8 g L-1 MgSO4 center dot 7H(2)O. The model prediction of 179 x 10(6) U g DCW-1 enzyme yield at optimum conditions was experimentally verified. This value is higher than any value obtained in the initial experiments as well as in the previously reported studies. The response surface methodology was found to be useful in improving the production of recombinant TaqI endonuclease in E. coli. (c) 2004 Elsevier Ltd. All rights reserved.Publication Metadata only Genome-Scale Metabolic Model of a Microbial Cell Factory (Brevibacillus thermoruber 423) with Multi-Industry Potentials for Exopolysaccharide Production(MARY ANN LIEBERT, INC, 2019) TOKSOY ÖNER, EBRU; Yildiz, Songul Yasar; Nikerel, Emrah; Oner, Ebru ToksoyBrevibacillus thermoruber 423 is a thermophilic bacterium capable of producing high levels of exopolysaccharide (EPS) that has broad applications in nutrition, feed, cosmetics, pharmaceutical, and chemical industries, not to mention in health and bionanotechnology sectors. EPS is a natural, nontoxic, and biodegradable polymer of sugar residues and plays pivotal roles in cell-to-cell interactions, adhesion, biofilm formation, and protection of cell against environmental extremes. This bacterium is a thermophilic EPS producer while exceeding other thermophilic producers by virtue of high level of polymer synthesis. Recently, B. thermoruber 423 was noted for relevance to multiple industry sectors because of its capacity to use xylose, and produce EPS, isoprenoids, ethanol/butanol, lipases, proteases, cellulase, and glucoamylase enzymes as well as its resistance to arsenic. A key step in understanding EPS production with a systems-based approach is the knowledge of microbial genome sequence. To speed biotechnology and industrial applications, this study reports on a genome-scale metabolic model (GSMM) of B. thermoruber 423, constructed using the recently available high-quality genome sequence that we have subsequently validated using physiological data on batch growth and EPS production on seven different carbon sources. The model developed contains 1454 reactions (of which 1127 are assigned an enzyme commission number) and 1410 metabolites from 925 genes. This GSMM offers the promise to enable and accelerate further systems biology and industrial scale studies, not to mention the ability to calculate metabolic flux distribution in large networks and multiomic data integration.Publication Metadata only Investigation of anti-cancer activity of linear and aldehyde-activated levan from Halomonas smyrnensis AAD6(T)(ELSEVIER, 2014) TOKSOY ÖNER, EBRU; Sarilmiser, Hande-Kazak; Oner, Ebru ToksoyThe main aim of this study was to investigate the potential role of levan polysaccharide in developing polysaccharide-based anticancer therapeutics. Moreover, by periodate oxidation, chemically modified forms of levan harboring increasing amounts of aldehyde groups were obtained and characterized. All the samples were found to be biocompatible when treated with the mouse fibroblast cell line L929. Anticancer activities of levan and its derivatives were investigated in A549 (human lung adenocarcinoma), HepG2/C3A (human liver hepatocellular carcinoma), AGS (human gastric adenocarcinoma), and MCF-7 (human breast adenocarcinoma) cell lines and were found to depend on the dose as well as on the cell type. The observed decrease in cancer cell viability was shown to be due to apoptosis via luminogenic-based caspase-3/7 activity assay. This study established the high potential of these levan-based polymers in developing polysaccharide-based nanocarrier systems for anti-cancer drugs. (C) 2014 Elsevier B.V. All rights reserved.Publication Metadata only From healing wounds to resorbable electronics, levan can fill bioadhesive roles in scores of markets(IOP PUBLISHING LTD, 2019) TOKSOY ÖNER, EBRU; Combie, Joan; Oner, Ebru ToksoyLevan is a fructose homopolysaccharide which gained attention recently for its unusual combination of properties distinguishing it from other natural biodegradable polysaccharides like chitosan, cellulose or starch. Among the strongest bioadhesives, film-forming levan is garnering interest for its role in some simple solutions to difficult problems. One of these is illustrated by the elegant research using laser-based techniques to construct levan films for healing wounds and burned tissue. Another is the development of bioresorbable electronic implants. Levan has been found in habitats as diverse as salterns and thermal waters to tropical plants and sugar factories. This review of the low viscosity, levan adhesive describes the mechanisms by which it forms bonds and the reasons behind some of its practical and industrial applications. Here we present descriptions from the literature for feasible approaches ready to transition from the laboratory to those searching for answers in fields as varied as medicine, packaging and furniture assembly.Publication Metadata only Exopolysaccharides from extremophiles: from fundamentals to biotechnology(TAYLOR & FRANCIS LTD, 2010) TOKSOY ÖNER, EBRU; Nicolaus, Barbara; Kambourova, Margarita; Oner, Ebru ToksoyExopolysaccharides (EPSs) make up a substantial component of the extracellular polymers surrounding most microbial cells in extreme environments like Antarctic ecosystems, saline lakes, geothermal springs or deep sea hydrothermal vents. The extremophiles have developed various adaptations, enabling them to compensate for the deleterious effects of extreme conditions, e.g. high temperatures, salt, low pH or temperature, high radiation. Among these adaptation strategies, EPS biosynthesis is one of the most common protective mechanisms. The unusual metabolic pathways revealed in some extremophiles raised interest in extremophilic microorganisms as potential producers of EPSs with novel and unusual characteristics and functional activities under extreme conditions. Even though the accumulated knowledge on the structural and rheological properties of EPSs from extremophiles is still very limited, it reveals a variety in properties, which may not be found in more traditional polymers. Both extremophilic microorganisms and their EPSs suggest several biotechnological advantages, like short fermentation processes for thermophiles and easily formed and stable emulsions of EPSs from psychrophiles. Unlike mesophilic producers of EPSs, many of them being pathogenic, extremophilic microorganisms provide non-pathogenic products, appropriate for applications in the food, pharmaceutical and cosmetics industries as emulsifiers, stabilizers, gel agents, coagulants, thickeners and suspending agents. The commercial value of EPSs synthesized by microorganisms from extreme habitats has been established recently.Publication Metadata only Conformational analysis of sulfated and unmodified levan polysaccharides via molecular dynamics simulations(ELSEVIER SCIENCE BV, 2016) TOKSOY ÖNER, EBRU; Oner, Ebru Toksoy; Coskunkan, Binnaz; Turgut, Deniz; Rende, Deniz; Bucak, Seyda; Baysal, Nihat; Ozisik, Rahmi