Shift-down in growth rate rather than high cell density induces toxic shock syndrome toxin-1 gene expression in Staphylococcus aureus.

A luciferase-based reporter system for the expression of the toxic shock syndrome toxin-1 gene (tst) of Staphylococcus aureus FRI 1187 was used in continuous culture to determine whether high cell density on transient shift-down or shift-up of specific growth rate (mu) induced expression of tst. Little expression occurred at steady state at a low dilution rate (D) and in a transient period of increasing mu. However, a rapid and approximately 130-fold increase in expression occurred during a transient shift-down of mu. These findings suggest reduction of mu is a key element in the control of tst expression.