Mechanistic Studies on the Formation and Functionality of High Molecular Levans from Acetic Acid Bacteria

The exopolysaccharide levan is synthesized by the enzyme levansucrase, which is secreted into the environment by specific microorganisms. Levan consists of β-(2,6)-linked β-D-fructose units and is a natural component of many bacterial biofilms and fermented foods. In contrast to other food biopolymers, levan has unique functional properties that make it particularly interesting for various technological applications. Thus, many attempts have been made to optimize the yield of levan using suitable production organisms. In only a few of these studies the molecular weight, which is described as extremely variable, has been correlated with the functional properties of levan. As a result, there is a lack of thorough knowledge on the use of levan with specifically selected properties limiting the application of levan in food systems. Previous studies have shown that levan from acetic acid bacteria of the genus Gluconobacter have exceptional high molecular sizes and unique macromolecular properties. But it is not understood how acetic acid bacteria can form such high molecular weights under certain conditions and why the functional properties of high molecular weight levan vary from those of low molecular weight levan.The main goal of this project is to establish systematic correlations between the natural formation, the molecular weight, and the resulting macromolecular and functional properties of levan from acetic acid bacteria. The findings will enable a controlled production and provide a profound and expanded understanding of the complex synthesis of levan with tailor-made properties. To achieve the project goal, physiologically and enzymatically controlled mechanisms of the formation of levan are correlated with its molecular weight. In addition, molecular weight-, solvent-, and concentration-dependent conformational changes as well as molecular interactions of levan in aqueous systems are investigated and molecular mechanisms for the functionalities turbidity and gel formation are derived.The outcomes of the proposed project enable the development of novel process strategies for the controlled fermentative or enzymatic production of levan with defined properties in food matrices. Moreover, the findings enable the establishment of previously unused levan functionalities in other areas such as the biotechnology and material science. The systematic investigations of natural formation mechanisms and properties of levan should furthermore provide deeper insights into the biosynthesis of microbial polysaccharides during bacterial biofilm formation. In addition, the findings serve as the basis for the comprehensive assessment of complex biotechnological processes to produce biomacromolecules with tailor-made functionalities.

Summary report of the project

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