Dextran from Sucrose

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. 

Prepare lOOOmL apple juice Rogosa agar (Section 13.6.1). 

Filter sterilize the sucrose solution through a 0.45 pm membrane and aseptically add to the tempered agar medium. 

Once solidified, streak each test strain on the agar medium and incubate at 25°C/77°F for approximately 2 weeks before examining the culture for dextrans using a sterile needle. 

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In 1861, Louis Pasteur1 reported a polysaccharide that was produced from sucrose. In 1874, Scheubler2 determined its empirical formula and named it dextran. The formation of polysaccharide (dextran) was observed as the result of bacterial transformation of sucrose solutions into viscous solutions, gels, and/or flocculent precipitates.3 The synthesis of dextran from sucrose by a cell-free... 

Bailey obtained dextransucrases from cultures of a rumen strain of S. bovis grown on a series of carbohydrates in the presence of carbon dioxide. A preparation of the enzyme, purified by precipitation from a D-glucose medium with ammonium sulfate, contained less than 4% of dextran, and appeared to synthesize a (l- 3)-branched dextran from sucrose. ... 

A reducing disaccharide, consisting of D-glucose and D-fructose, named levjcrose 214) is formed in the reaction mixture to the extent of about 3 % during the synthesis of dextran from sucrose by an enzyme isolated from the microorganism Leuconostoc mesenteroides. Its specific rotation is [a]o —6.8° (in water) m.p. 161-162°C. Methylation studies show that its structure is 5-0-a-D-glucopyranosyl-D-fructopyranose. 

In commercial production, enzymes from a strain of Leuconostoc mesente-roides are used to synthesize dextran from sucrose, water, essential minerals, and vitamins (see under Synthesis, below). The native dextran so obtained is then carefully hydrolyzed to the proper molecular-weight average and recovered by fractional precipitation from solution with methanol (1 8). 

VIII. SYNTHESIS OF DEXTRAN 1. Dextran from Sucrose... 

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]. 

It should not produce dextran from sucrose or mannitol from fructose. If mannitol appears, it should be able to ferment it rapidly. 

A reducing disaccharide, composed of D-glucose and D-fructose and named leucrose was isolated in 7.9% yield from the reaction mixture produced by the synthesis of dextran from sucrose by an enzyme from Leuconosioc mesenteroides NRRLB-512A. Methylation and other evidence showed that this disaccharide is 0-a-D-glucopyranosyl-(i -> 5)-fructop5n anose. 

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