Variations in surface polymers of Streptococcus mutans

Dispensable genes and foreign DNA in Streptococcus mutans

A range of properties, including the ability to utilize various sugars, bind macromolecules and produce mutacins, are known to vary in their occurrence in different strains of Streptococcus mutans. In addition, insertion-sequence elements show a limited distribution and sequencing of the genome of S. mutans UA159 has revealed the presence of putative genomic islands of atypical base composition indicative of foreign DNA. PCR primers flanking regions suspected of having inserted DNA were designed on the basis of the genome sequence of S. mutans UA159 and used to explore variation in a collection of 39 strains isolated in various parts of the world over the last 40 years. Extensive differences between strains were detected, and similar insertion/deletion events appear to be present in the genomes of strains with very different origins. In two instances, insertion of foreign DNA appears to have displaced original S. mutans genes. Together with previous results on the occurrence of deletions in genes associated with sugar metabolism, the results indicate that S. mutans has a core genome and a dispensable genome, and that dispensable genes have become widely distributed through horizontal transfer.

Effect of whole saliva on the rheologic behavior of extracellular water-soluble glucan produced by Streptococcus mutans

The viscosity of mixtures of Streptococcus mutans water-soluble glucan and stimulated whole saliva or buffer was measured at pH 5, 6, 7, and 8. The viscosity was measured as a function of shear rate in the range 15 s-1-230 s-1. Though the centrifuged saliva had a viscosity close to that of water it increased the viscosity of the glucan up to 65% at pH 6 and 55% at pH 7 and at a shear rate of 20 s-1, indicating an interaction between saliva components and glucan that could be an important part of the cohesive forces of plaque matrix. The interaction between saliva and glucan was less pronounced at pH 5 and 8, which indicates a charge-dependent interaction. The viscosity increase at pH 6 and 7 was higher at low than at high shear rates, suggesting a higher contribution to plaque stability when weak as opposed to high mechanical forces are exerted on the plaque.

Inter-serotype comparison of polysaccharides produced by extracellular enzymes from Streptococcus mutans

The biochemical and morphological characteristics of polysaccharides synthesized from sucrose by extracellular enzymes from D-glucose-grown Streptococcus mutans representing serotypes a-g were compared. The polysaccharides synthesized by the enzymes from serotypes a, d, and g formed visible aggregates and firmly adhered to glass surfaces, whereas those formed by the enzymes from serotypes b, c, e, and f floated homogeneously and were poorly adherent. The enzymes of serotypes a, d, and g produced large amounts of water-insoluble polysaccharides (IPs, D-glucans), and those of serotypes b, c, e, and f water-soluble polysaccharides (SPs, D-glucans and D- fructans ). As compared with the IPs of serotypes b, c, e, and f, the IPs of serotypes a, d, and g (a) contained a higher proportion of (1----3)-alpha-D-glucosidic linkages and alpha-D-(1----3,6) branch linkages; (b) showed higher susceptibility to (1----3)-alpha-D-glucanase (serotype a excepted) and lower (1----6)-alpha-D-glucanase sensitivity; (c) contained larger amounts of high-molecular-weight fractions; (d) showed higher intrinsic viscosities (serotype b excepted); and (e) had lower S. mutans cell-agglutination activities. On electron-microscope observation, the IPs of all serotypes showed two fibrillar components; a double-stranded fibril, with short, fluffy protrusions extending out of its periphery, and a fine, single-stranded fibril. Thus, the serotypes could be divided into two major groups: a, d, and g; and b, c, e, and f. No similar grouping of serotypes was indicated by the chemical and morphological properties of SPs.

Teichoic acids from chemostat-grown cultures of Streptococcus mutans and Lactobacillus plantarum

We examined the effect of growth conditions in chemostat culture on the quantity and composition of the cell wall teichoic acids of Streptococcus mutans BHT and Lactobacillus plantarum NCIB 7220 and the membrane lipoteichoic acid from S. mutans Ingbritt. With the cell wall teichoic acids, which are covalently linked to peptidoglycan, the amount of teichoic acid is independent of the growth conditions employed. However, the extent of glucosyl substitution of the polymer from L. plantarum was dependent on growth conditions. S. mutans Ingbritt lipoteichoic acid, on the other hand, was little affected by growth conditions in terms of composition or serological activity, but the amount produced was markedly affected by changes in growth conditions.

Effect of fructose and other carbohydrates on the surface properties, lipoteichoic acid production, and extracellular proteins of Streptococcus mutans Ingbritt grown in continuous culture

Streptococcus mutans Ingbritt was grown in a chemostat at destined dilution rates in either 0.5% fructose or 0.5% sorbitol and at destined pH values in 0.5% fructose. The yield of cells was affected by the carbohydrate source, as well as by the pH, with the lowest yield being at pH 5.5 in 0.5% fructose. Fructose-grown cells showed greater susceptibility to lysis by a muramidase than the corresponding glucose-grown cells, but there were no marked differences in the lytic susceptibilities of the corresponding cell wall preparations or in the serological reactivities of wall lysates with antiserum to S. mutans Ingbritt. The greatest amounts of cellular lipoteichoic acid were obtained at high dilution rates in both fructose and sorbitol, as well as at high pH values in fructose. The greatest amounts of extracellular lipoteichoic acid were found at low dilution rates, as estimated by rocket immunoelectrophoresis and also by hemagglutination. Three major extracellular protein components were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the effects of growth conditions on these components were determined. Results for batch-grown cultures showed that there was genotypic variation in the susceptibility of cells to lysis by a muramidase. The enhancement of lipoteichoic acid production by fructose and sorbitol in batch cultures was not identical in representative strains of S. mutans serotype c, nor was the effect of fructose found uniformly in representative strains of the different S. mutans serotypes.

Extracellular polysaccharide synthesized by the oral bacterium Streptococcus mutans of serotype a to e in vitro

Extracellular polysaccharide (EPS) synthesized in vitro by Streptococcus mutans belonging to serotypes a, b, c, d and e was shown to consist mainly of glucan. Only strains of type b and e regularly produced substantial amounts of fructan, too. Strains of type d synthesized significantly higher quantities of glucan than strains of the other types per gram of bacterial mass. The percentage of insoluble glucan was lowest in samples from strains of type a and c, and highest in samples from strains of type d. In contrast to the insoluble glucan, the linkage pattern of the soluble glucan of the five types showed only small differences. The percentage of alpha-1,3-linked glucose units was highest in the insoluble glucan from strains of type d and e, and lowest in glucan from type c. The differences were significant. Incubation of Strep. mutans under various culture conditions showed that the quantities and composition of EPS formed depend on the culture condition used. The effect of culture conditions, however, was similar for all strains. Therefore the differences found with respect to the quantities and composition of EPS synthesized in vitro by Strep. mutans of different types are apparently type-dependent.