Inhibitory effects of endo-α-1,3-glucanase on glucan film formation and glucan synthesis by the glucosyltransferase of the oral bacterium Streptococcus mutans

Abstract

Glucan film formed on glass by the action of cell-free glucosyltransferase prepared from Streptococcus mutans OMZ176 was not removed by treatment with high concentrations of purified endo-α-1,3-glucanase from Streptomyces chartreusis strain F2. However, de-novo formation of a glucan film on glass was significantly inhibited by the presence of α-1,3-glucanase at low concentrations. The presence of increasing amounts of α-1,3-glucanase in glucan-synthesizing mixtures resulted in decreased production of water-insoluble (WIS) glucan and increased production of water-soluble (WS) glucan. WIS glucan produced in the presence of α-1,3-glucanase contained higher proportions of α-1,3-linked glucose residues than did WIS glucan produced in the absence of this enzyme; the presence of α-1,3-glucanase resulted in synthesis of WS glucan containing lower proportions of α-1,3-linkages. With increasing concentrations of α-1,3-glucanase, the number of both α-1,6- and α-1,3-linkages was lower in WIS glucans and higher in WS glucans formed. The modified WIS glucans possessed lower intrinsic viscosity than control glucans, but retained high mol. wt, whereas the modified WS glucans remained unchanged in viscosity, but had lower mol. wt. These results suggest that endo-α-1,3-glucanase reduces WIS glucan production by suppressing synthesis of α-1,3-linkages and by solubilizing a portion of the WIS glucan molecule. The resulting decreased α-1,6-linkage content appears to contribute to decreased viscosity of WIS glucan. The combined effect of these glucanase-mediated actions is the inhibition of the formation of a glucan film on glass.