THE REGULATION OF fepE GENE BY THE PMRA/B TWO COMPONENET SYSTEM IN SALMONELLA TYPHIMURIUM

ESTELA CERASUOLO; ROBERTO MORERO; MÓNICA A. DELGADO

Mar del Plata-Buenos Aires

Congreso; XLIII Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology; 2007

SAIB

The lipopolysaccharide (LPS) is the outermost component of the cell envelope in Gram (-) bacteria.  It consists of the hydrophobic lipid A, a short non-repeating core oligosaccharide and a distal polysaccharide termed O-antigen. We report here the regulation of fepE gene, which product determines the O-antigen very long chain (35 to 100 O-antigen subunits) attached to the lipid A-core. We show that the PmrA/PmrB two-component system, which controls the modification of the lipid A, promotes directly the fepE transcription, when Salmonella experiences PmrA/PmrB-inducing conditions. The PmrA/PmrB system consists of the response regulator PmrA that is activated by Fe3+, the signal sensed by its sensor PmrB; and by low Mg2+, in a PhoP/PhoQ-dependent pathway. The transcriptional induction of fepE increased the amount of O-antigen very long chain, but can not modify the resistance to the serum complement-mediated killing. Nevertheless, we show that the deletion of pbgE2E3 and wzzB genes, which are also induced by the PmrA regulator, resulted in an O-antigen without the region containing 1 to 15 or 16 to 35 O-antigen subunits, respectively, and decreased the sensitivity to serum complement. These results indicated that the PmrA/B system is the master regulator of the LPS synthesis, and that both O-antigen formation and the lipid A modification are required at the same time in Salmonella.