Person: TOKSOY ÖNER, EBRU
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TOKSOY ÖNER
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Publication 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 ToksoyFructans, 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.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 Open Access Fructans of the saline world(PERGAMON-ELSEVIER SCIENCE LTD, 2018-09) TOKSOY ÖNER, EBRU; Kirtel, Onur; Versluys, Maxime; Van den Ende, Wim; Oner, Ebru ToksoySaline and hypersaline environments make up the largest ecosystem on earth and the organisms living in such water-restricted environments have developed unique ways to cope with high salinity. As such these organisms not only carry significant industrial potential in a world where freshwater supplies are rapidly diminishing, but they also shed light upon the origins and extremes of life. One largely overlooked and potentially important feature of many salt-loving organisms is their ability to produce fructans, fructose polymers widely found in various mesophilic Eubacteria and plants, with potential functions as storage carbohydrates, aiding stress tolerance, and acting as virulence factors or signaling molecules. Intriguingly, within the whole archaeal domain of life, Archaea possessing putative fructan biosynthetic enzymes were found to belong to the extremely halophilic class of Halobacteria only, indicating a strong, yet unexplored link between the fructan syndrome and salinity. In fact, this link may indeed lead to novel strategies in fighting the global salinization problem. Hence this review explores the unknown world of fructanogenic salt-loving organisms, where water scarcity is the main stress factor for life. Within this scope, prokaryotes and plants of the saline world are discussed in detail, with special emphasis on their salt adaptation mechanisms, the potential roles of fructans and fructosyltransferase enzymes in adaptation and survival as well as future aspects for all fructanogenic salt-loving domains of life.Publication 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.Publication 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.Publication Metadata only Review of Levan polysaccharide: From a century of past experiences to future prospects(PERGAMON-ELSEVIER SCIENCE LTD, 2016) TOKSOY ÖNER, EBRU; Oner, Ebru Toksoy; Hernandez, Lazar; Combie, JoanLevan is a fascinating beta-(2,6)-linked fructose polymer with an unusual,combination of properties characterized in this review. In nature, levan is synthesized from sucrose by a wide range of microorganisms and a few plant species. Bacterial levans often have molecular weights over 500,000 Da, are commonly branched, and form compact nanospheres offering a broad spectrum of applications. The most relevant genetic, biochemical and structural aspects of the biosynthetic enzyme levansucrase are detailed. Optimization of parameters for levan production by intact bacteria and by the isolated enzyme is surveyed. The diversity of current and potential applications of levan is illustrated by a discussion of uses ranging from personal care and aquaculture to the medical and food industries. (C) 2016 Elsevier Inc. All rights reserved.Publication 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 ToksoyFructans 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.