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

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.