Leuconostoc mesenteroides, dextran produced from sucrose

The majority of dextrans in nature are produced extracellularly via dextran-sucrase from sucrose by several lactic acid bacteria, principally Leuconostoc and Streptococcus species [13]. Dextran is also synthesised by dextrinase of different Gluconobacter species [56]. Referring to this enzyme, fermentation of maltodextrins leads to a- —4) branched dextrans with comparatively lower Mw. However, dextransucrase from Leuconostoc mesenteroid.es NRRL B-512F has attracted most interest because of commercial use. 

The number of enzymes responsible for the formation of polysaccharides from sucrose is also restricted. The two best known enzymes that form polysaccharides from sucrose are the dextran, synthesized by the microorganism Leuconostoc mesenteroides (8) and related organisms, and the levan, produced from the same substrate by Acetobacter levanicum (9) and other species. 

Leuconostoc mesenteroides and Leuconostoc ssp. are found in fermented foods of plant origin [11]. The occurrence of these bacteria in sugar refineries is responsible for problems in filtration processes because of increased viscosity by the presence of soluble dextran [12,13]. Furthermore, dextran retards the rate of crystallisation of sucrose and adversely affects the crystal shape. The occurrence of dextran in the matrix of dental plaque results from certain Streptococcus strains [14]. The principle organism, Streptococcus mutans, is able to produce water-soluble glucan (named dextran) and water-insoluble... 

Dextrans are polysaccharides composed of linear glucose residues. They are produced from a polysaccharide synthesized by the bacteria Leuconostoc mesenteroides grown on sucrose media. Dextrans... 

Dextran Sucrose. Dextrans are produced by the bacteria Leuconostoc mesenteroides from sucrose. The reaction is catalyzed by a glucotrans-ferase, which has been purified and which produces little if any free glucose.Similar enzymes appear to be present in other bacteria. The reaction catalyzed by dextran sucrase is ... 

Some lactic acid bacteria have the ability to metabolize sucrose to produce polymers known as dextrans (viscous, slimy). While most strains of Oeno-coccus oeni are negative for this attribute (Edwards et al., 1991), some strains of Lactobacillus (Edwards et al., 1993) and Leuconostoc mesenteroides (Garvie, 1984) are positive. The outlined method originates from Pilone and Kunkee (1972). To test for dextran formation, touch a sterile inoculating needle straight down into an isolated colony and move the needle straight back up. A positive reaction is one where threads or strands are drawn up on the needle. 

In the nineteenth century, there were reports of a mysterious thickening and sometimes gelling of cane and beet sugar solutions. Pasteur [148] reported in 1861, that these viscous fermentations of sucrose resulted from microbial action. Sucrose solutions were observed to be converted into viscous solutions, gels, and/or flocculent precipitates [149]. The material that produced such changes in the sucrose solutions was isolated and found to be a polysaccharide that was called dextran [150]. Van Tieghem isolated and named the bacterium that produced the polysaccharide, Leuconostoc mesenteroides [151]. 

The synthesis of dextran from sucrose by a cell-free bacterial culture filtrate was first reported by Hehre in 1941 [152]. The genera of bacteria that are recognized to produce enzymes capable of synthesizing polysaccharides from sucrose are principally Leuconostoc and Streptococcus. These genera are gram positive, facultatively anaerobic cocci that are very closely related to each other. One notable difference between them is that the L. mesenteroides strains required sucrose in the growth medium to induce the formation of the enzyme(s), whereas the Streptococcus species did not require sucrose in the medium to form the enzymes [153]. 

Leuconostoc species may be satisfactorily cultured on a variety of carbohydrates, but, for the production of dextransucrases, sucrose must be included in the nutrient medium indeed, it has been suggested that the enzyme-induction process may be triggered by the n-fructofuranosyl group of the sucrose molecule. In consequence of this condition, preparations of dextransucrases from Leuconostoc species have contained various proportions of dextran that could not be removed by any fractionation procedures available. The presence of this tenaciously boimd dextran, once regarded as an integral part of the dextransucrase molecule, has presented a major obstacle to further study of the enzyme. Stacey and associates attempted to produce a dextran-free enzyme by growing L. mesenteroides NRRL B-1375 on a sucrose mediiun contain-... 

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