Person: TOKSOY ÖNER, EBRU
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
TOKSOY ÖNER
First Name
EBRU
Name
6 results
Search Results
Now showing 1 - 6 of 6
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 Simultaneous modeling of enzyme production and biomass growth in recombinant Escherichia coli using artificial neural networks(ELSEVIER, 2008) TOKSOY ÖNER, EBRU; Gunay, M. Erdem; Nikerel, I. Emrah; Oner, Ebru Toksoy; Kirdar, Betuel; Yildirim, RamazanIn this work, the biomass growth and the TaqI endonuclease production by recombinant Esherichia coli were studied using artificial neural networks. The effects of the medium components on biomass growth and enzyme yield were modeled by various networks. After the most successful networks were statistically determined, they were used to extract additional knowledge such as the possible correlations between the biomass growth and the enzyme yield, and the relative significance of the medium components. It was found that the change of the biomass growth and the enzyme yield with the change of KH2PO4 concentration was strongly correlated with an R-value of -0.954. Some mild correlations were also observed for the other components. It was also found that the relative significances of the medium components were in the same order for both outputs: (NH4)(2)HPO4 Concentration was determined as the most important parameter followed by the glucose, KH2PO4 and MgSO4 concentrations. (C) 2008 Elsevier B.V. All rights reserved.Publication Metadata only Evaluation of industrial Saccharomyces cerevisiae strains for ethanol production from biomass(PERGAMON-ELSEVIER SCIENCE LTD, 2012) KASAVİ, CEYDA; Kasavi, Ceyda; Finore, Ilaria; Lama, Licia; Nicolaus, Barbara; Oliver, Stephen G.; Oner, Ebru Toksoy; Kirdar, BetulFive industrial Saccharomyces cerevisiae strains were evaluated for their suitability for strain improvement for future use in ethanol production processes. Principal components analysis of growth-related and production-related fermentation parameters of the 5 strains grown on glucose demonstrated the superiority of the Y9 strain in terms of its rapid growth and highest ethanol yields on both biomass and glucose. The growth and ethanol production performances of these strains on various agro-industrial wastes (including sugar beet pulp, starch and sugar beet molasses) and biological residues (including carrot, tomato and potato peel) were also determined. Ethanol tolerance studies, using both solid and liquid cultures, revealed the remarkable abilities of the BC187 and Y9 strains to survive and grow at high ethanol concentrations. Suspension cultures were found to be highly tolerant to 78.80 g L-1 ethanol however their growth ability showed a distinct decrease with increasing ethanol concentration such that only (1-2)% of the control growth was observed in media containing 118.20 g L-1 ethanol. The importance of choosing the appropriate S. cerevisiae strain to be used in ethanol production was clearly established with this study. Fermentation performances of the cultures under different cultivation conditions pointed to the fact that the choice of strain will not only depend on the ethanol tolerance but also on the preferential utilization of the carbon resources of biological residues. (c) 2012 Elsevier Ltd. All rights reserved.Publication Metadata only Molasses as fermentation substrate for levan production by Halomonas sp.(SPRINGER, 2011) TOKSOY ÖNER, EBRU; Kucukasik, Faruk; Kazak, Hande; Guney, Dilvin; Finore, Ilaria; Poli, Annarita; Yenigun, Orhan; Nicolaus, Barbara; Oner, Ebru ToksoyLevan is a homopolymer of fructose with many outstanding properties like high solubility in oil and water, strong adhesiveness, good biocompatibility, and film-forming ability. However, its industrial use has long been hampered by costly production processes which rely on mesophilic bacteria and plants. Recently, Halomonas sp. AAD6 halophilic bacteria were found to be the only extremophilic species producing levan at high titers in semi-chemical medium containing sucrose, and in this study, pretreated sugar beet molasses and starch molasses were both found to be feasible substitutes for sucrose. Five different pretreatment methods and their combinations were applied to both molasses types. Biomass and levan concentrations reached by the Halomonas sp. AAD6 cells cultivated on 30 g/L of pretreated beet molasses were 6.09 g dry cells/L and 12.4 g/L, respectively. When compared with literature, Halomonas sp. was found to stand out with its exceptionally high levan production yields on available fructose. Molecular characterization and monosaccharide composition studies confirmed levan-type fructan structure of the biopolymers. Rheological properties under different conditions pointed to the typical characteristics of low viscosity and pseudoplastic behaviors of the levan polymers. Moreover, levan polymer produced from molasses showed high biocompatibility and affinity with both cancerous and non-cancerous cell lines.Publication Metadata only Effective stimulating factors for microbial levan production by Halomonas smyrnensis AAD6(T)(SOC BIOSCIENCE BIOENGINEERING JAPAN, 2015) TOKSOY ÖNER, EBRU; Sarilmiser, Hande Kazak; Ates, Ozlem; Ozdemir, Gonca; Arga, Kazim Yalcin; Oner, Ebru ToksoyLevan is a bioactive fructan polymer that is mainly associated with high-value applications where exceptionally high purity requirements call for well-defined cultivation conditions. In this study, microbial levan production by the halophilic extremophile Halomonas smyrnensis AAD6(T) was investigated systematically. For this, different feeding strategies in fed-batch cultures were employed and fermentation profiles of both shaking and bioreactor cultures were analyzed. Initial carbon and nitrogen source concentrations, production pH, NaCl and nitrogen pulses, nitrogen and phosphorous limitations, trace elements and thiamine contents of the basal production medium were found to affect the levan yields at different extends. Boric acid was found to be the most effective stimulator of levan production by increasing the sucrose utilization three-fold and levan production up to five-fold. This significant improvement implied the important role of quorum sensing phenomenon and its regulatory impact on levan production mechanism. Levan produced by bioreactor cultures under conditions optimized within this study was found to retain its chemical structure. Moreover, its biocompatibility was assessed for a broad concentration range. Hence H. smyrnensis AAD6(T) has been firmly established as an industrially important resource microorganism for high-quality levan production. (C) 2014, The Society for Biotechnology, Japan. All rights reserved.Publication Metadata only The Genome-Based Metabolic Systems Engineering to Boost Levan Production in a Halophilic Bacterial Model(MARY ANN LIEBERT, INC, 2018) TOKSOY ÖNER, EBRU; Aydin, Busra; Ozer, Tugba; Oner, Ebru Toksoy; Arga, Kazim YalcinMetabolic systems engineering is being used to redirect microbial metabolism for the overproduction of chemicals of interest with the aim of transforming microbial hosts into cellular factories. In this study, a genome-based metabolic systems engineering approach was designed and performed to improve biopolymer biosynthesis capability of a moderately halophilic bacterium Halomonas smyrnensis AAD6(T) producing levan, which is a fructose homopolymer with many potential uses in various industries and medicine. For this purpose, the genome-scale metabolic model for AAD6(T) was used to characterize the metabolic resource allocation, specifically to design metabolic engineering strategies for engineered bacteria with enhanced levan production capability. Simulations were performed in silico to determine optimal gene knockout strategies to develop new strains with enhanced levan production capability. The majority of the gene knockout strategies emphasized the vital role of the fructose uptake mechanism, and pointed out the fructose-specific phosphotransferase system (PTSfru) as the most promising target for further metabolic engineering studies. Therefore, the PTSfru of AAD6(T) was restructured with insertional mutagenesis and triparental mating techniques to construct a novel, engineered H. smyrnensis strain, BMA14. Fermentation experiments were carried out to demonstrate the high efficiency of the mutant strain BMA14 in terms of final levan concentration, sucrose consumption rate, and sucrose conversion efficiency, when compared to the AAD6(T). The genome-based metabolic systems engineering approach presented in this study might be considered an efficient framework to redirect microbial metabolism for the overproduction of chemicals of interest, and the novel strain BMA14 might be considered a potential microbial cell factory for further studies aimed to design levan production processes with lower production costs.