Secretion of fructosyltransferase by Streptococcus salivarius involves the sucrose-dependent release of the cell-bound form

Three strains of Streptococcus salivarius including a recent clinical isolate were found to possess Ca2(+)-dependent fructosyltransferase (FTF) activity. The extracellular FTF activity of cells grown on sucrose increased as much as 9-fold compared with cells grown on either glucose, fructose or galactose. This increase in activity was due not to induction of FTF by sucrose, but to the release of the cell-bound form of the enzyme. Studies with washed cells of S. salivarius ATCC 25975 showed that the extent of release of the cell-bound FTF activity was dependent upon the sucrose concentration up to 4 mM, at which concentration maximum release (95%) of cell-bound FTF occurred. Several lines of evidence suggested that either substrate binding or de novo synthesis of fructan is required for the release of the cell-bound FTF activity.