Levan, formation

Harrison, Tarr and Hibbert96 investigated the production of levan from sucrose by the action of Bacillus subtilis Cohn and B. mesentericus Trevisan. Nutrient solutions containing 10% carbohydrate, 0.1% peptone, 0.2% disodium hydrogen phosphate and 0.5% potassium chloride were incubated at 37° for six days. Levan formation occurred only with sucrose and raffinose, and not with melezitose, lactose, maltose, D-xylose, D-glucose or D-fructose. It was therefore suggested that only those carbohydrates with a terminal D-fructofuranose residue were satisfactory substrates for levan formation. 

However, some carbohydrates with a terminal D-fructofuranose residue are not suitable substrates for levan formation, e. g., methyl /3-d-fructofuranoside and inulin,64 even in the presence of enzymes98 which hydrolyze these substrates. 

Hestrin, Avineri-Shapiro and Aschner9 report that levan formation by means of B. subtilis is greater if cultural products other than levan are continually removed by dilution or dialysis. The organism was inoculated into a phosphate-buffered solution contained in a cellophane bag suspended in a large volume of sucrose peptone solution. 

The specificity of levansucrase98 is dependent not only on the d-fructoside but also on the aldoside residue of the substrate. Neither inulin nor methyl D-fructofuranoside was hydrolyzed by levansucrase, and even when these two substrates were hydrolyzed by inulase (prepared from inulin-fermenting Torula yeast) or by yeast invertase respectively, no levan formation occurred with levansucrase. However, neither methyl D-fructofuranoside nor inulin inhibited levan formation from sucrose by levansucrase. No levan was formed from potassium D-glucose... 

Owen conducted experiments on sucrose inoculated with yeast and with organisms of the potato group, e. g., B. mesenterieus, B. vulgatus, and found that levan formation was very markedly reduced by excessive inversion in the presence of the yeast (or of yeast invertase) or by the addition of excess invert sugar. Apparently the nascent D-fructose liberated by yeast is not in a suitable condition for polymerization to levan. On the other hand (page 217), symbiotic association of L. mesenteroides with Saccharomyces cerevisiae produces much larger yields of dextran. ... 

Fig. 13 Inulin and levan formation by fructosyltransferase from sucrose...

The synthesis of cellulose by A. xylinum from various polyalcohols14 is accompanied by the formation of carbon dioxide, formic acid, nonvolatile acids, ketoses and sometimes ethanol. The much greater variety of substrates suitable for cellulose synthesis, as compared with the small number for dextran or levan, may account for the widespread natural occurrence of cellulose. 

The occurrence of fructosans in plants is widespread (see page 253).M The formation of a bacterial fructosan, levan, by a number of different organisms has also been investigated. 

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. 

Bacillus delbrucki, emulsins, V, 63 Bacillus knemieniewski, polysaccharide formation by, II, 220 Bacillus leoaniformans, levan formed by, II, 226... 

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