Fractionation and Properties of Glucans Produced by Streptococcus mutans

Abstract

Water-insoluble (ISG) and water-soluble (SG) fractions of glucans produced by cell-free glucosyltransferase of Streptococcus mutans AHT (serotype g ) were isolated by centrifugation at 20,000 × g for 15 min. No further resolution of slightly sonicated ISG was observed with gel filtrations on any Bio-Gel beads, including A-50m. Bio-Gel P-100 filtration subdivided SG into two fractions with higher and lower molecular weights (designated SG-A and SG-B, respectively). SG-A was further resolved into two subfractions, SG-A-I and SG-A-II, by 10 to 40% and 50 to 80% ethanol precipitation, respectively. Relative amounts of ISG, SG-A-I, SG-A-II, and SG-B were 66.3:9.4:4.4:19.9. The molecular sizes of these fractions were >1.5 × 10 7 , ≧1.5 × 10 7 , ≦5 × 10 6 (>1 × 10 5 ), and ≦1 × 10 4 daltons, and their α-1,3 glucosidic linkage contents were approximately 35, 35, 16, and 4% for fractions ISG, SG-A-I, SG-A-II, and SG-B, respectively. Both ISG and SG-A-I were resistant to hydrolysis by dextranase and possessed the ability to aggregate with concanavalin A and to agglutinate S. mutans cells. SG-A-II had extremely low dextranase susceptibility and significant agglutinating activities, whereas SG-B showed high dextranase sensitivity and neither aggregating nor agglutinating activity. These results indicate that SG of S. mutans AHT consists of three types of glucans with distinctly different molecular sizes and chemical structures and strongly suggest that the ISG and SG-A-I fractions are different physical states of an inherently identical glucan. Preliminary observations suggest that the glucans produced by other S. mutans strains of several serotypes may be similarly classified.