A Quantitative Study of the Production of Dextran from Sucrose by Rumen Strains of Streptococcus bovis

Summary auto-generated

Bailey and Oxford (1958) quantitatively studied dextran production by Streptococcus bovis strains isolated from rumen. They demonstrated that S. bovis produces water-soluble dextran from sucrose, similar chemically to Leuconostoc dextran but with less branching. The key requirement for dextran production was carbon dioxide availability, either as gas or provided through HCO₃⁻ buffering—most strains produced little or no dextran in strict anaerobiosis without CO₂. An initial CO₂ concentration of at least 0.005 M was necessary. The researchers characterized the polysaccharide as having α1→6 glucosidic linkages as the major bonds, confirmed through chromatographic detection of isomaltose, periodate oxidation, and optical rotation measurements. Optimal dextran yields (up to 80% conversion of available anhydroglucose) were achieved with pH control and CaCO₃ presence, along with additional sucrose supplementation during incubation. Tween 80 partially substituted for CO₂ in stimulating production. Fructose and a reducing fructose-containing disaccharide accumulated in cultures during dextran formation.

Key findings

Rumen Streptococcus bovis strains require CO₂ or HCO₃⁻ for appreciable dextran production from sucrose, unlike the heterofermentative Leuconostoc species
The dextran produced is biochemically similar to Leuconostoc dextran with α1→6 glucosidic linkages as the major structure, though with less α1→3 branching
Optimal dextran yields (nearly 80% conversion) were achieved with CaCO₃ buffering, pH control, and supplemental sucrose addition during culture
Minimum CO₂ concentration of 0.005 M (as HCO₃⁻) was necessary for good dextran production in closed systems
Fructose and reducing oligosaccharides consistently accumulated in high dextran-producing cultures

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Abstract

SUMMARY: Freshly isolated and old stock strains of Streptococcus bovis originating from the rumen will produce dextran at 37° in liquid sucrose-containing media. For good yields the presence of CO₂ in some form is necessary. The CO₂ may be provided as HCO^-₃ at the start or during the life of the culture or by incubation in a CO₂ atmosphere. The dextran has [α]²⁰_d + 187° to + 190° and is similar chemically to the leuconostoc dextran save that branching of the α 6 linked anhydro-glucose chain is rarer. With some strains practically no dextran is formed in H₂ as gas-phase or in a closed system without HCO^-₃ from which air is excluded. Other strains seem to have a limited power of producing dextran under these conditions, possibly because their action is not entirely homofermentative. Tween 80 will partially replace CO₂ even with the first kind of strain. Highest yields of dextran, up to 80% of the anhydro-glucose provided, are obtained when the life of the culture is prolonged by repeated neutralization and when additional sucrose is supplied. This is best achieved by the continuous neutralization obtained when solid CaCO₃ is present in the culture. Dextran production is always accompanied by accumulation of fructose in the culture liquid together with a reducing fructose-containing disaccharide. Dextran can sometimes be produced in a simple liquid sucrose + proteose peptone medium with no phosphate buffering. Other things being equal, the presence of CO₂ or HCO^-₃ does not greatly increase the yield of bacterial protein in sucrose media.