Effects of dextranases on cell adherence, glucan-film formation and glucan synthesis by Streptococcus mutans glucosyltransferase

Abstract

Adherence of heat-killed Streptococcus mutans AHT cells to glass, induced by incubation with sucrose and cell-free AHT glucosyltransferase (GTF), was markedly inhibited by dextranases at concentrations as low as 45 mU/ml or less. Formation of glucan film on glass from sucrose by GTF was also repressed by dextranases to a similar extent. The low levels of dextranase significantly suppressed water-insoluble (WIS) glucan formation, which was compensated by the increased production of water-soluble (WS) glucans. Higher concentrations, up to 360mU/ml, of dextranases inhibited the production of both WS and WIS glucans. The WIS glucans produced in the presence of dextranase contained a high proportion of α-1,3 (α-1,3,6)-linked glucose residues in contrast to native glucans, whereas both native and modified WS glucans had the almost identical relative proportions of α-1,6 (α-1,)- and α-1,3 (α-1,3,6)-linked glucose residues. The modified WS and WIS glucans were significantly low in intrinsic viscosity, molecular size and ability to agglutinate Strep, mutans cells as compared with control glucans. It was concluded that dextranase markedly represses WIS glucan production, reduces adhesiveness and cell-agglutinating activity of the glucans by lowering their α-1,6 linkage contents and molecular weights, and thus inhibits the formation of glucan film and adherence of Strep, mutans cells on glass.