1. Exploring the Capacity of Halophilic Microorgansisms to Synthesize Exopolysaccharides with Interesting Properties

Margarita Kambourova

Although microbial exopolysacchaides (EPSs) have been intensively studied during the last two decades, the knowledge on these compounds is still scarce due to the phylogenetic diversity of microbial producers and the complexity of their molecules. Halophilic producers have been described in both bacterial and archaeal domains. Most of them require sugar and organic nitrogen for high yield synthesis. Halophiles synthesize molecules containing different monosaccharides, aminosugars, sulphates, uronic acids. Investigations into the halophilic EPS properties reveal their biotechnological potential in the field of the bio-medical applications, food products as emulsifiers and gelling agents, bioremediation for removing of toxic compounds, heavy metal removal, and in the petroleum industry for an enhanced oil recovery. The current review aims to increase the basic knowledge on EPS production by halophiles focusing on the recent investigations on halophilic producers of EPSs, culture conditions for attaining high yield, chemical composition and structure of their molecules, and the potential applications based on their physico-chemical properties.

2. Sources, Biosynthesis, Properties, Structures and Applications of Halophilic Exopolysaccharides

Annarita Poli, Paola Di Donato, Ilaria Finore, Luigi Leone and Barbara Nicolaus

Saline and hypersaline environments such as natural saline seas, lakes, coastal lagoons, marine salterns, deserts, saline soils, etc. are considered extreme habitats for microbial life. They harbor halophiles as well as halotolerant microorganisms growing in the absence of salt and in the same time tolerant to relatively high salt concentrations. Halophilic microorganisms suggest many advantages for biotechnological exploration like relatively short time course of fermentations, lack of pathogenicity and the production of stable biomolecules, such as exopolysaccharides (EPS), under the extreme conditions of the most industrial processes. The aim of this review is to present a summary of the status of the research about the structures and the biosynthesis of exopolysaccharides by halophilic microorganisms, including medium-released and biofilm embedded polysaccharides. Moreover, relationships between the structure and the function of the exopolysaccharides and their possible biotechnological and industrial applications, are discussed.

3. Exopolysaccharide Production by Thermophilic Microorganisms

Songul Yasar Yildiz

In recent years, the demand for natural polymers for various industrial applications led to increased interest in microbial exopolysaccharide (EPS) production. Several microorganisms have the ability to synthesize extracellular polysaccharides either as soluble or insoluble polymers. Among those, EPS from thermophilic microorganisms are of special interest owing to its advantages such as short fermentation time, better oxygen mass transfer, decreased viscosity of synthesized polymer and the corresponding culture and the non-toxic nature of the polymer allowing applications in food and pharmaceutical industries. Despite this interest, there is very limited knowledge on EPS biosynthesis mechanisms by thermophilic bacteria, as opposed to the vast amount of reports on mesophilic EPS producers. In this review, we present a brief overview of life under extreme environmental conditions especially high temperatures. This is followed by a discussion of thermophilic microorganisms and their adaptation mechanisms, and specifically focuses on the production of EPSs and their ecological and physiological functions. The application areas of industrially important EPSs from various thermophilic producer strains are also mentioned.

4. Engineering of Microbial Polysaccharide Structures

Jochen Schmid

This review will deal with the structural diversity of bacterial (exo)polysaccharides based on the biosynthesis pathways and the highly specific glycosyltransferase proteins. Especially the so called Wzx/Wzy biosynthesis pathway will be explained in detail and the challenges and prospects of tailoring the chemical structures and thus polysaccharide properties will be highlighted. The differences of chemical modification and in-vivo modification will be discussed. Finally, genetic engineering approaches for altered chemical structures and enhanced productivities will be displayed and discussed to highlight challenges and prospective for engineering hetero- as well as homopolysaccharides.

5. Microbial Exopolysaccharides Based Drug Delivery Systems

Aynur Muduroglu Kirmizibekmez, Songul Yasar Yildiz and Özlem Ateş Duru

Microbial exopolysaccharides (EPSs), one of the main groups of microbially produced biopolymers, have long been accepted as significantly important biomaterials in industrial areas. Therefore there is an increased interest in microbial EPSs that show great diversity and functions with unique and commercially relevant material properties. These biodegradable, biocompatible, both human and environmental friendly polysaccharides have many uses as drug delivery vehicles, controlled drug carriers or scaffolds for tissue engineering, implantable biomaterials, etc. In this chapter, after a brief description of main principles and routes of drug delivery and microbial exopolysaccaharides, the microbial EPSs xanthan, dextran, levan, gellan, and curdlan are discussed in more detail with a special focus on their uses in drug delivery systems.

6. Fructan Biosynthesis in Bacteria

Lázaro Hernández, Yamira Quintero and Alexis Musacchio

In nature, fructans are synthesized from sucrose by a relative low number of plant species and a wide range of microorganisms, including bacteria, archaea, and fungi. Levan, the predominant bacterial fructose polymer, is a biofilm-forming exopolysaccharide that fulfills diverse biological roles. The biosynthetic enzyme levansucrase (EC 2.4.1.10) catalyzes sucrose hydrolysis, sucrose fructosylation, and fructan polymerization, as the three main activities. The hydrolase/transferase ratio, the spectrum of fructan products, and the overall levan yield vary depending on the intrinsic properties of each enzyme and the reaction conditions. This review provides a detailed update on the most relevant genetic, biochemical, structural, and evolutionary aspects of levansucrase. Several levan-producing bacteria are enzymatically equipped to utilize the polymer as an alternative carbon source under starving conditions. The last section describes how the strictly controlled transcription of levanase genes ensures the prevalence of levan synthesis over degradation whenever exogenous sucrose is available as an energetic substrate.

7. Exopolysaccharides from Genus Weissella and their Functional Applications

Rwivoo Baruah and Arun Goyal

The microbial exopolysaccharides that have a wide variety of applications are predominantly produced by Lactic acid bacteria (LAB). In recent times the focus on Weissella, a specific genus of LAB, has grown. In the genus Weissella two species, cibaria and confusa are the major producer of exopolysaccharides (EPS). These species chiefly produce the exopolysaccharide "dextran" a biopolymer of D-glucose. The physicochemical properties of dextran from Weissella makes it uniquely suitable for several food applications. Besides dextran the genus Weissella has been also reported to produce heteropolysaccharides containing alternating monomers such as mannose and galactose and also capsular polysaccharides (EPS covalently bound to the cells). Variety of applications using exopolysaccharide from Weissella such as improving the texture of bread in baking, its anti-oxidative and immunomodulatory properties are known. The ability to produce high amount of exopolysaccharides by members of genus Weissella have led to the development of novel food products such as quinoa-based yogurt made using dextran producing Weissella cibaria. This review describes the different types of EPS produced by genus Weissella and their characteristics with the functional properties.

8. Fructans as Natural, Bioactive Cosmeceutical Ingredients

Merve Erginer Hasköylü, Margarita Kambourova and Ebru Toksoy Öner

Fructans have novel characteristics and have many applications in cosmetic market as bioactive ingredient or rheology and formulation improver. Cosmeceuticals are not only used for aesthetic reasons but also for the treatment of ailments. Here in this review we focus on cosmeceuticals, applications, natural polysaccharides and their needs, fructans and their usage and activity in cosmetic formulations. Main attention is paid on fructan based skin care cosmeceuticals (moisturizing, antiaging, and whitening) based on new formulations with natural ingredients. The annual exponential growth of consumers that are fully aware of natural, and bioactive ingredients determines the special impact of this review for evaluation the future of the pharmaceutical industry.

9. Levan as a Bioactive Material for Medical Applications

Sinem Selvin Selvi̇, Elif Pi̇ranlioğlu, Tuğçe Doğruel, Edina Eminagic, Muhammed Yusuf Kandur and Ebru Toksoy Öner

Levan is a fructan homopolymer with β-(2, 6) glycosidic bonds between its fructose monomers and can be obtained from plants and numerous microorganisms. This extracellular polysaccharide distinguishes from other natural polysaccharides with its unique properties and hence, its wide range of possible applications have been studied thoroughly in the past decade resulting with interesting findings related to its wound healing, heparin-mimetic, anti-cancer, anti-inflammatory, antiviral, non-toxic, antihyperlipidemic, hypocholesterolemic, hyperglycaemic inhibitory and anti-AIDS properties. Besides medical properties, it is also digestible by human gastrointestinal (GI) tract and shows prebiotic activity allowing it to be used in functional foods. This review will mainly focus on levan polysaccharide and its medical applications such as bioactive carrier in drug delivery systems and bioactive surfaces produced by laser technologies.

10. Molecular Modification of Levan and Biotechnological Applications of its Derivatives

Edmilson Clarindo de Siqueira, Bogdan Doboszewski, Juliana de Souza Rebouças, Irapuan Oliveira Pinheiro, Ebru Toksoy Öner and Fabio Rocha Formiga

Levan is a fructose-based homopolymer, a fructan, with emerging potential in different fields, including biotechnology, food and health. It is obtained from sucrose by a wide range of microorganisms. Levan has become a versatile biopolymer due to its physicochemical and biological properties stemming from its molecular weight, functional groups and degree of substitution. Levan can undergo changes in its molecular structure to broaden its functional properties and consequently its applications. Molecular modification methods mainly involve chemical, physical and biological changes. Chemical modification is the most widely used method to enhance the bioactivity of levan, which occurs through the addition or substitution of functional groups. Physical and biological modifications alter only the molecular weight into varied sizes. This review offers a description of the main molecular modification methods of levan and the contributions to its physicochemical and biological properties.

11. Cloning and Partial Characterization of an Extracellular Dextransucrase Coding Region (DSR-V) from Leuconostoc citreum M-3   Free download

Reinaldo H. Fraga Vidal, Sandra Pacios Michelena, Roberto C. Arísticas Ribalta, Lisandra Martínez Valdés, Meinardo Lafargue Gámez, Amanda Montes Alvarez, Magali Remaud-Siméon and Pierre Monsan

The dextransucrase enzymes synthesize dextran, a glucose polymer with broad industrial applications, making the search for new dextransucrases of great interest. The work described aimed at the partial characterizing of a recombinant dextransucrase enzyme from Leuconostoc citreum M-3. From the genomic DNA of strain M-3, an amplicon containing a coding region of a dextransucrase called DSR-V was isolated, and deposited in the GenBankTM (Accession number: KF724950). The amino acid sequence alignment of DSR-V with other dextransucrases demonstrated that it shares a 94% identity with the DSR-D of L. mesenteroides Lcc4 and the DSR-S of L. mesenteroides NRRL B-512F. The DSR-V was cloned and expressed in Escherichia coli JM109 facilitating the formation and detection of DSR-V specific dextran. The SDS-PAGE soluble fraction zymography of E. coli DSR-V and the 13C-NMR spectra of dextran polymers synthesized by this clone confirm that L. citreum M-3 dsrV gene codes for a different dextransucrase synthesizing linear dextrans with mainly α(1-6) linkages.