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TOKSOY ÖNER, EBRU

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Mühendislik Fakültesi

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TOKSOY ÖNER

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EBRU

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Now showing 1 - 9 of 9

Open Access
Levansucrase from Halomonas smyrnensis AAD6(T): first halophilic GH-J clan enzyme recombinantly expressed, purified, and characterized
(SPRINGER, 2018-11) TOKSOY ÖNER, EBRU; Kirtel, Onur; Menendez, Carmen; Versluys, Maxime; Van den Ende, Wim; Hernandez, Lazaro; Oner, Ebru Toksoy
Fructans, homopolymers of fructose produced by fructosyltransferases (FTs), are emerging as intriguing components in halophiles since they are thought to be associated with osmotic stress tolerance and overall fitness of microorganisms and plants under high-salinity conditions. Here, we report on the full characterization of the first halophilic FT, a levansucrase from Halomonas smyrnensis AAD6(T) (HsLsc; EC 2.4.1.10). The encoding gene (lsc) was cloned into a vector with a 6xHis Tag at its C-terminus, then expressed in Escherichia coli. The purified recombinant enzyme (47.3kDa) produces levan and a wide variety of fructooligosaccharides from sucrose, but only in the presence of high salt concentrations (>1.5M NaCl). HsLsc showed Hill kinetics and pH and temperature optima of 5.9 and 37 degrees C, respectively. Interestingly, HsLsc was still very active at salt concentrations close to saturation (4.5M NaCl) and was selectively inhibited by divalent cations. The enzyme showed high potential in producing novel saccharides derived from raffinose as both fructosyl donor and acceptor and cellobiose, lactose, galactose, and -arabinose as fructosyl acceptors. With its unique biochemical characteristics, HsLsc is an important enzyme for future research and potential industrial applications in a world faced with drought and diminishing freshwater supplies.
Open Access
Synthesis and characterization of interpenetrating network (IPN) based levan-polyacrylamide hydrogels and their application in conservation of cultural heritage
(2023-11-01) ÜNAL YILDIRIM, SEMRA; OKTAR, FAİK NÜZHET; GENÇ, SEVAL; TOKSOY ÖNER, EBRU; Özen Sağlam R., Ünal Yıldırım S., Oktar F. N., Genç S., Erdem G., Toksoy Öner E.
In this study, an IPN based enzymatic levan-polyacrylamide hydrogel (EL-PA) was developed and characterized for its structural, morphological, rheological properties and swelling kinetics to underline hydrogel properties and its potential use in paper conservation. The addition of levan also led to changes in the viscoelastic behavior of the hydrogels, with the complex viscosity of EL-PA samples showing pronounced dependence on shear rate. The swelling and the overall surface area of the hydrogels were increased with the addition of levan into the polymer network. Source associated structural differences were found to be negligible such that both microbially produced linear and enzymatically produced branched forms of levan performed equally well. Solvent loaded hydrogels were then applied on an artifact, a 19th century book of Namık Kemal, and investigated using FTIR, SEM, XRD and colorimetric analysis. Old adhesive layers were successfully removed, and hydrogels showed good compatibility and ease of application. This study has shown that levan has improved hydrogel properties and levan based systems bear high potential in conservation science.
Open Access
Biosynthesis of Levan by Halomonas elongata 153B: Optimization for Enhanced Production and Potential Biological Activities for Pharmaceutical Field
(2022-01-01) TOKSOY ÖNER, EBRU; Erdal Altıntaş Ö., TOKSOY ÖNER E., ÇABUK A., AYTAR ÇELİK P.
Halophilic organisms are a novel attractive option as cell factories for the production of industrially valuable bioproducts. Halomonas elongata is the cell factory of choice for ectoine production, but its levan production has not been well researched. Based on this scientifc motivation, in this study, we evaluated the chemical and biological properties of levan produced by the halophilic extremophile Halomonas elongata 153B (HeL). First, the central composite design was used to determine the optimal process variables for maximum levan biosynthesis. Then, the levan produced from HeL was purifed, quantifed, and chemically characterized with FTIR, 1 H-NMR, and GPC analyses. This was followed by antioxidant, anti-infammatory, antibioflm, and antimicrobial activity tests to assess its biological activities as well as a cytotoxcity assay. Maximum levan yields of 5.13±0.38 g/L were achieved after dialysis at the optimum levels of process variables. The 1 H-NMR spectrum of HeL revealed characteristic signals. It showed a strong antioxidant activity of 67.88% and the best radical scavenger. At a concentration of 400 µg/mL, HeL showed the most anti-infammatory efcacy. Also, at all indicated concentrations (250, 500, 750, and 1000 μg/mL) HeL, acted against bioflms formed by Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 11778, Candida albicans ATCC 10231. Furthermore, HeL displayed antimicrobial activities against all strains tested. Finally, HeL showed high Cell viability in all dosages and no cytotoxicity was observed. In light of these results, HeL may have high potential in the medical, pharmaceutical and dermo-cosmetics industries.
Open Access
Co-production of levan with other high-value bioproducts: A review
(2023-04-30) TOKSOY ÖNER, EBRU; de Siqueira E. C., TOKSOY ÖNER E.
Levan is a homopolysaccharide of fructose that has both scientific and industrial importance, with various applications in health, pharmaceutical, cosmetic and food industries. Despite its broad spectrum of uses, there are only a limited number of commercial levan sources due to the high costs related to its production. To make production economically viable, efforts have been concentrated on the selection of levan-producing microorganisms, the genetic manipulation of new strains, and the use of inexpensive agro-industrial byproducts as substrates. Another efficient strategy involves the concomitant synthesis of other products with high market value and as such, the successful co-production of levan was demonstrated with fructooligosaccharides, ethanol, sorbitol, poly-ε-lysine, poly-γ-glutamic acid and polyhydroxyalkanoates. This paper offers a systematic review of important aspects regarding recent strategies involving the simultaneous synthesis of levan and other bioproducts of aggregate value reported to date and discusses the challenges and opportunities for its large-scale production and applications.
Open Access
Production of a high molecular weight levan by Bacillus paralicheniformis, an industrially and agriculturally important isolate from the buffalo grass rhizosphere
(2022-09-01) TOKSOY ÖNER, EBRU; Nasir A., Ahmad W., Sattar F., Ashfaq I., Lindemann S. R., Chen M., Van den Ende W., TOKSOY ÖNER E., Kirtel O., Khaliq S., et al.
A new exopolysaccharide (EPS) producing Gram-positive bacterium was isolated from the rhizosphere of Bouteloua dactyloides (buffalo grass) and its EPS product was structurally characterized. The isolate, designated as LB1-1A, was identified as Bacillus paralicheniformis based on 16S rRNA gene sequence and phylogenetic tree analysis. The EPS produced by LB1-1A was identified as a levan, having beta(2 -> 6) linked backbone with beta(2 -> 1) linkages at the branch points (4.66%). The isolate LB1-1A yielded large amount (similar to 42 g/l) of levan having high weight average molecular weight (Mw) of 5.517 x10(7) Da. The relatively low degree of branching and high molecular weight of this levan makes B. paralicheniformis LB1-1A a promising candidate for industrial applications.
Open Access
Discovery of fructans in Archaea
(ELSEVIER SCI LTD, 2019-09) TOKSOY ÖNER, EBRU; Kirtel, Onur; Lescrinier, Eveline; Van den Ende, Wim; Oner, Ebru Toksoy
Fructans are fructose-based oligo-and polysaccharides derived from sucrose that occur in a plethora of Eubacteria and plants. While fructan-producing (fructanogenic) Eubacteria are abundant in hypersaline environments, fructan production by Archaea has never been reported before. Exopolysaccharides accumulated by various Archaea from the Halobacteria class (belonging to the genera of Halomicrobium, Haloferax and Natronococcus) originating from different locations on Earth were structurally characterized as either levans or inulins with varying branching degrees (10%-16%). Thus, we show for the first time in the literature that fructans are produced in all three domains of life, including Archaea. This proof of concept will not only provide insight into Archaeal glycans and evolution but it may also open new frontiers for innovative strategies to overcome the ever-increasing threat of excessive salinization.
Open Access
Production and characterization of a high molecular weight levan and fructooligosaccharides from a rhizospheric isolate of Bacillus aryabhattai
(ELSEVIER, 2020-04) TOKSOY ÖNER, EBRU; Nasir, Anam; Sattar, Fazal; Ashfaq, Iram; Lindemann, Stephen R.; Chen, Ming-Hsu; Van den Ende, Wim; Oner, Ebru Toksoy; Kirtel, Onur; Khaliq, Shazia; Ghauri, M. Afzal; Anwar, Munir A.
Bacillus aryabhattai GYC2-3 strain, capable of synthesizing EPS, was isolated from the rhizosphere of Taraxacum spp. plant. The EPS was identified as levan by C-13 NMR spectroscopy and methylation analysis. The levan produced had a high weight average molecular weight of 5.317 x 10(7) Da and degree of branching 5.19%. Thin layer chromatography and high-performance anion-exchange chromatography revealed that it is capable of producing broad range of fructooligosaccharides (FOS) and higher levels of FOS synthesis were observed with increasing sucrose concentrations. The optimum temperature, initial pH and sucrose concentration for levan biosynthesis were studied to be 30 degrees C, 8.0 and 250 g/L, respectively. Levan production was increased by similar to 38% (26 g/L) when provided aeration as compare to static cultures. To the best of our knowledge, this is the first report on biosynthesis of levan and FOS by a B. aryabhattai strain.
Open Access
Genomic analysis reveals the biotechnological and industrial potential of levan producing halophilic extremophile, Halomonas smyrnensis AAD6T
(SPRINGER INTERNATIONAL PUBLISHING AG, 2015-12) TOKSOY ÖNER, EBRU; Diken, Elif; Ozer, Tugba; Arikan, Muzaffer; Emrence, Zeliha; Oner, Ebru Toksoy; Ustek, Duran; Arga, Kazim Yalcin
Halomonas smyrnensis AAD6T is a gram negative, aerobic, and moderately halophilic bacterium, and is known to produce high levels of levan with many potential uses in foods, feeds, cosmetics, pharmaceutical and chemical industries due to its outstanding properties. Here, the whole-genome analysis was performed to gain more insight about the biological mechanisms, and the whole-genome organization of the bacterium. Industrially crucial genes, including the levansucrase, were detected and the genome-scale metabolic model of H. smyrnensis AAD6T was reconstructed. The bacterium was found to have many potential applications in biotechnology not only being a levan producer, but also because of its capacity to produce Pel exopolysaccharide, polyhydroxyalkanoates, and osmoprotectants. The genomic information presented here will not only provide additional information to enhance our understanding of the genetic and metabolic network of halophilic bacteria, but also accelerate the research on systematical design of engineering strategies for biotechnology applications.
Open Access
Understanding the effects of chitosan, chia mucilage, levan based composite coatings on the shelf life of sweet cherry
(2023-08-01) TOKSOY ÖNER, EBRU; Mujtaba M., Ali Q., Yilmaz B. A., Seckin Kurubas M., Ustun H., ERKAN M., Kaya M., Cicek M., Oner E. T.
Sweet cherry (Prunus avium L.) fruits are prone to quality and quantity loss in shelf-life conditions and cold storage due to their short post-harvest life. Until now efforts have been made to extend the shelf life of the sweet cherry. However, an efficient and commercially scalable process remains elusive. To contribute to this challenge, here in this study, biobased composite coatings consisting of chitosan, mucilage, and levan, were applied on sweet cherry fruits and tested for postharvest parameters in both market and cold storage conditions. Results demonstrated that the shelf life of sweet cherries can be extended until the 30th day while retaining important post-harvest properties like decreased weight loss, fungal deterioration, increased stem removal force, total flavonoid, L-ascorbic acid, and oxalic acid. Given the cost-effectiveness of the polymers used, the findings of this study indicate the feasibility of extending the shelf-life of sweet cherries on a larger scale.