Journal of Dental Research, Vol 66, 1364-1369, Copyright © 1987 by International & American Associations for Dental Research Online Journals
Ultrastructure of extracellular polysaccharides produced by serotype c Streptococcus mutans
Y. Toda, I. Moro, T. Koga, H. Asakawa and S. Hamada
The ultrastructure of extracellular polysaccharides produced in colonies by
two clinical isolates and that of a nitrosoguanidine-induced mutant of
serotype c Streptococcus mutans with different polysaccharide-synthesizing
abilities were compared electron-microscopically. A large amount of
polysaccharide was produced from sucrose by colonies of typical serotype c
strain MT8148R and a clinical variant MT6801R with an enhanced
fructan-synthesizing ability. Transmission electron-microscopy (TEM)
revealed that the polysaccharides consisted of three structural components,
i.e., globular, single-stranded filamentous, and double-stranded fibrillar
structures. These structures were ascribed to production of fructan,
water-soluble glucan, and water-insoluble glucan, respectively. On the
other hand, two kinds of structures, a globular body and an amorphous
substance, were observed by scanning electron-microscopy (SEM). The former
was composed of fructan, while the latter contained a mixture of
water-soluble and water-insoluble glucans which formed filamentous and
double-stranded fibrillar structures under TEM. Very small quantities of
polysaccharides were formed in colonies of mutant NG7183, which was derived
from S. mutans MT6801R. This strain was found to possess low glucan- and no
fructan-synthesizing abilities. The polysaccharides produced in colonies of
mutant NG7183 were composed only of filamentous and double-stranded fibrils
under TEM. A small amount of amorphous substance was observed by SEM in
colonies of NG7183.
