Fructans bacterial

Two gram-positive bacterial genera. Bacillus and Streptococcus, have species that elaborate fructansucrases that synthesize fructans from sucrose. Bacillus levani- 

Xanthan is elaborated in a submerged aerobic fermentation process. The primary carbon source is 2-3% (w/v) D-glucose, although sucrose and starch can also be used. During the fermentation, the viscosity of the culture liquor progressively increases. After the fermentation is complete, the liquor is diluted with water to lower the viscosity, and the cells are removed. The xanthan is then precipitated by the addition of methanol or 2-propanol to 50% (v/v) to the cell-free liquor in the presence of 2% (w/v) potassium chloride. 

Xanthan consists of a repeating pentasaccharide unit containing two D-glucose residues, two D-mannose residues, and one D-glucuronic acid residue. The main chain is essentially cellulose with the D-glucopyranosyl units linked P-1 4. A 

Xanthan has found a number of commercial applications due to its emulsion-stabilizing and particle-suspending properties, the small variation in its viscosity with changes in temperature, and its tolerance for high salt concentrations. It is the 

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Particularly preferred polysaccharides are inulin, levans from plants, and bacterial fructans. Suitable glycol-specific oxidizing agents include sodium periodate, or lead tetra acetate. Examples of reducing agents include sodium borohydride and sodium cyano-borohydride (38). 

L. is formed by hydrolysis of - hydroxymetltyl furfural in an equimolecular mixture with formic acid. Starting materials are - fructose, - high-fhictose syrups as well as natural or bacterial - fructans. Yields of 70% can be obtained. 

Two extracellular D-fructans, (2- 6)-linked S-D-fructofuranan or levan and the less common corresponding (2 l)-linked polysaccharide, of the inulin type, are elaborated by different bacteria. These polysaccharides are formed from sucrose by the action of sucrose fructosyltransferases. Terminal )S-D-fructofuranosyl groups are present in some bacterial heteropolysacchar-... 

Fructan was harvested by precipitation from the culture broth by addition of ethanol or isopropanol. Acetone and methanol can also be used. The yield and consistency of the product varied depending on the amount of alcohol added. The fructan started to precipitate at the medium/alcohol v/v ratio of 1 1.2, and the yield peaked at about 1 1.5. Further increase in the ratio hardened the fructan and made the product less fluid. Slightly less isopropanol was needed than ethanol to precipitate levan (fructan). Although most of the bacterial cells, unfermented sugars, and other solubles remained in the aqueous alcohol phase, pre-removal of microbial cells by centrifuging was needed to obtain a pure form of fructan. The product was further purified by repeated precipitation and dissolution in water, followed by dialysis or ultrafiltration. The final product was an... 

Structure. The nmr spectra, shown in Figure 2, indicates that essentially all fructose molecules in the polymers are in the same conformation. In Table I, nmr peaks from fructan are compared to peaks from known inulin 0-(l->2) linked) and bacterial levan (P-(2->6) linked). Data clearly show the fructan to be of the p-(2- 6) type (27). (Sec Table II.)... 

Polysaccharides that exclusively contain D-fructose are known as fructans and there are two known kinds, inulin and levan. Inulin is a polysaccharide containing -D-fructofuranose linked (2 1) [118]. Inulins are found in the roots and tubers of the family of plants known as the Compositae, which includes asters, dandelions, dahlias, cosmos, burdock, goldenrod, chicory, lettuce, and Jerusalem artichokes. Other sources are from the Liliacae family, which includes lily bulbs, onion, hyacinth, and tulip bulbs. Inulins are also produced by certain species of algae [119]. Several bacterial strains of Streptococcus mutans also produce an extracellular inulin from sucrose [120]. 

Bacterial exopolysaccharides (extracellular polysaccharides) include those that are made from sucrose, viz., dextrans and fructans. Dextrans are branched a-glucans containing (1 3) and/or (1 6) and occasionally (1 2) linkages. Fructans contain -D-fructofuranosyl units linked (2 6) or (2 1). 

This obvious structural difference between plant and bacterial inulin has its origin in the individual synthesis related system. Feedstock for both inulins is sucrose. However, the plant inulin production is a two-step reaction, starting with a sucrose-1-fructosyltransferase (1-SST). One sucrose molecule acts as donor and a second one as acceptor of a fructosyl unit. This leads to the formation of the trisaccharide 1-kestose. Catalyzed by a fructan-fructan-1-fructosyltransferase (1-FFT), fructosyl units are shuffled between the 1-kestose and higher polymeric p-(2 1) linked fructan molecules in the second step. Repetition of this step results in inulin with (3-(2 1) linkages only [129-132]. 

Only the fructosyltransferase (FTF, EC 2. 4. 1. 9) is required in bacteria for the synthesis of bacterial inulin. The enzyme shuffles fructosyl units from one sucrose molecule (acting as druior) to another sucrose molecule, 1-kestose, and higher polymeric p-(2 1) linked fructan molecules, respectively (acting as acceptor). This enzyme partly leads to p-(2—>6) linkages, which results in branches within the inulin molecule [130, 133]. 

Fructose occurs rarely in the bacterial polysaccharide. It has been found in the LPS of several Vibrio species [108] and in the K4 [109] and Kll [110] capsular antigens of Escherichia coli. In all cases, fructose appears as a terminal residue. In several plant species, fructans consisting of p-D-fructofuranosyl units are present as important storage polymers. The structure of the polysaccharide isolated from B. caryophylli is different from those of the above polysaccharides however, as levan can be isolated as bacterial exopolysaccharides, this polysaccharide may be a side-product of levan biosynthesis. 

The basic mechanism is a disproportionation. Thus a disaccharide, such as sucrose, could give a triose and a free monosaccharide. Synthesis of a levan (i.e. a fructan) would be accompanied by the release of glucose, while the production of a dextran (i.e. a glucan) would liberate free fructose. By repeated transglycosylations of this type polymers arise. A similar mechanism occurs in the production of some plant fructans, but it is otherwise very rare in eukaryotes. Bacterial levans are usually much larger than their eukaryotic counterparts and other polymers produced in the same way include bacterial arabinans, xylans, galactans and glucans. 

Polymers of fructose are of widespread occurrence in plants, but are common only in a few orders, particularly the Compositae ind Graminae, They differ in several respects from prokaryotic fructans, especially in that they are intracellular rather than extracellular, that they are far smaller than their bacterial counterparts and that they contain relatively more glucose. Their function in plants is as storage polysaccharides and they are synthesised, ultimately from photosynthetic products. In bacteria such polymers are often assembled from exogenous, rather than endogenous disaccharides. 

The plant fructans are of two main types, the linear P2,6-fructans (levans) and the linear P2,l-fructans (inulins). A third class contains both types of linkage and is highly branched. Bacterial levans, by contrast, are mostly composed of a predominance of P2,6 sequences with P2,l branches at rather less frequent intervals than in the branched fructans of plants. Whereas bacterial levans have molecular weights often in excess of one million daltons, the plant fructans seldom reach one-hundreth of this size. 

For the production of bacterial inulin only the enzyme fructosyl transferase (FTF, EC 2.4.1.9) is required, which shuffles fructosyl units from the sucrose donor to another sucrose molecule or 1-kestose or higher polymeric p-(2- 1) linked fructan molecules acting as acceptor. The enzyme partly leads... 

Levans are synthesized in approximately all bacterial versions of fructan production, as well as being possible to produce by fracturing soybean mucilage. Levan, fructose-composed biopolymer of bacterial origin, has potential in biotechnology due to its prebiotic and immunostimulatory properties. It was suggested that the combination of levan and nutritionally important microelements in the form of NPs serves as a first step towards a novel 2 in 1 approach for food supplements to provide safe and efficient delivery of microelements for humans and support beneficial gut microbiota with nutritional oligosaccharides [68],... 

Fructans aspaiagosan. iiisan, sinistran, bacterial levans... 

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