The Role of SprIR Quorum Sensing System in the Regulation of 94 Invasion.

The bacteria 94 have a LuxI/LuxR type QS system consisting of AHL synthase SprI and the regulatory receptor SprR. We have previously shown that inactivation of the AHL synthase gene resulted in an increase in the invasive activity of correlated with an increased bacterial adhesion. In the present work, the effects of inactivation of the receptor SprR are studied. Our results show that inactivation of the receptor gene leads to an increase in bacterial invasion without any increase in their adhesion. On the other hand, inactivation of the gene increases the activity of the extracellular protease serralysin. Inactivation of the QS system does not affect the activity of the pore-forming toxin ShlA and prevents the ShlA activation under conditions of a limited concentration of iron ions typical of the human body. While the wild type strain shows increased invasion in the iron-depleted medium, deletion of its QS system leads to a decrease in host cell invasion, which is nevertheless similar to the level of the wild type grown in the iron-rich medium. Thus, inactivation of either of the two component of the LuxI/LuxR-type QS system leads to an increase in the invasive activity of these bacteria through different mechanisms and prevents invasion under the iron-limited conditions.