ИСТИНА

Serratia are facultative pathogens primarily causing nosocomial infections. The mechanisms of these infections are, however, poorly understood. We have previously found that the capability of bacteria Serratia proteamaculans to invade eukaryotic cells correlates with the actinase activity of intracellular metalloprotease protealysin (Tsaplina et al., 2009). Along with protealysin, the invasive activity of S. proteamaculans is mediated by pore-forming toxin hemolysin ShlA and extracellular protease serralysin. Many virulence factors of bacteria are regulated by the Quorum Sensing system (QS) that controls expression of specific genes in response to population density. The QS system is composed of a LuxI-type AHL synthase and a LuxRtype AHL receptor. Proteins of the LuxI type produce certain signaling molecules that are bound by receptors of the LuxR type. The aim of our work was to reveal the effect of inactivation of the Lux-type SprI gene on the known virulence factors and the invasive activity of S. proteamaculans. Inactivation of SprI gene (the strain was provided by Dr. Khmel I.A., Institute of Molecular Genetics RAS) results in a 2-fold increase of S. proteamaculans invasion and this increasing may be associated with increasing in adhesive activity of bacteria. This inactivation does not affect activity of the pore-forming toxin ShlA and serralysin, but results in the loss of the actinase activity of protealysin. By mass spectrometry, bacterial outer membrane protein OmpX may be a substrate for protealysin. This enzyme is homologous to the Salmonella Rck protein involved in the zipper-like entry mechanism. We suggest that inactivation of S. proteamaculans AHL synthase gene leads to the increased invasive activity of the bacteria presumably as a result of accumulation of outer membrane protein, and this effect is mediated by the loss of the protealysin activity.