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TOKSOY ÖNER, EBRU

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TOKSOY ÖNER

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2011 - 20163
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    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 Toksoy
    Levan 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.
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    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 Toksoy
    Levan 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.
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    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, Joan
    Levan 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.