Regulation of the secreted phospholipase PhlA and flagellar expression in S. marcescens.

CASTELLI, MARÍA EUGENIA; GARCÍA VÉSCOVI, ELEONORA

Tucumán

Congreso; XLV Reunión anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2009

SAIB

Serratia marcescens is a gram-negative enteric bacteria, that can become an opportunistic pathogen in immunocompromised hosts. Despite numerous reported S. marcescens infections and the emergence of antibiotic-resistant strains, the virulence mechanisms of this organism are poorly understood. S. marcescens secretes many extracellular proteins. Among these, the secreted phospholipase PhlA is the only described exoprotein that belongs to the flagellar regulon and is also secreted by the flagellar apparatus. We conducted a generalized insertional mutagenesis and screened for PhlA-deficient strains. We found that three independent mutations in the wec cluster, which impair the assembly of enterobacterial common antigen (ECA), provoked the inhibition of PhlA expression. We determined that in the ECA-defective strains, the transcriptional cascade that controls flagellar assembly was turned off due to the down-regulation of flhDC expression. We performed a second mutagenesis to identify the regulatory mechanism involved in this flagellar repression. Our results show that the inactivation of the ECA biosynthesis leads to the activation of the RcsCDB phosphorelay system which in turn represses flhDC. Although highly conserved in all enteric bacteria, the role of ECA remained largely uncharacterized. These findings open a new perspective on its physiological role.