Transglucosidase activity of rumen strains of Streptococcus bovis; structure of the dextran produced from sucrose.

Many extensive studies have been made on the glucose polymers, known as dextrans, whichare produced from sucrose by the transglucosidase activity of species in the genus Leucomostoc. Less work has been described, however, on similar polysaccharides produced from sucrose by streptococcal species. Niven, Smiley & Sherman (1941) reported that various strains of Streptococcus bovis, of unrecorded origin, produced from sucrose a polysaccharide which yielded glucose on hydrolysis and which was therefore assumed to be dextran. Hehre & Neil (1946) showed, mainly by serological tests, that many strains of 'viridans' streptococci isolated from the blood of patients with subacute bacterial endocarditis could convert sucrose into a polysaccharide indistinguishable from Leuconostoc dextran. S. bovis is itself in many respects a 'viridans' streptococcus (Topley & Wilson, 1946). Jeanes et al. (1954) measured, by periodate oxidation, the amounts of main-chain linkages (m-1:6) and branching linkages (a-1:3 and cx-1:4) in the dextrans produced by two strains of Streptococ viridans. These two dextrans were reported to contain 11 and 31% of a-1:3, and 4 and 2% of a-1:4-glucosidic linkages respectively. In contrast with these results Barker, Pautard, Siddiqui & Stacey (1955b) reported that the dextran produced from sucrose by an unidentified Streptooccus, isolated from ropey elderberry wine, contained only a-1:6-glucosidic linkages and was essentially unbranched. Recently Dain, Neal & Seely (1956) reported that with most strains ofS. bovis grown on sucroseagar mucoid colonies containing a glucose polymer were produced only if carbon dioxide was present. The effect of carbon dioxide on the production of this polysaccharide, in liquid sucrose media, by several strains of rumen S. bovis has been investigated in detail by Bailey & Oxford (1958). They found that most of the strains failed to produce dextran in such a medium unless carbon dioxide or HCO3ion was present. The polysaccharide appeared to be a dextran containing few, if any, branching linkages. In view of the lack of information on Streptococcus dextrans it was decided to investigate, in more detail, the structure of the dextrans produced by the S. bovis strains used in the above work. This paper reports the results obtained in a study of the dextrans produced by six strains of rumen S. bovis from sucrose at 370 in the presence of carbon dioxide. The effect of incubation temperature and of Mg2+ ions in the medium on dextran structure is also briefly described.