Background: Salmonella Typhimurium LPS structure is regulated by the PmrAB, PhoPQ, and RcsCDB systems. Results: Wzz st is required for lipid A modifications. PbgE 2 and PbgE 3 control formation of short O-antigen region. Conclusion: PmrAB system is the master regulator of LPS remodeling, modulating genes that modify lipid A, core, and O-antigen. Significance: Salmonella exhibits complex mechanisms to modulate its LPS, which influences host interaction.

The degree of polymerization of O-antigen from Salmonella enterica serovar Typhimurium is controlled by the products of the wzzs t and wzzfepE genes. In the present study we investigated the role of the PmrA/PmrB regulatory system in wzzfepE transcription. We report that the direct binding of the PmrA regulator to a specific promoter site induces the expression of the wzzfepE gene. This effect increases the amount of very long (VL) O-antigen, which is required for the resistance of Salmonella to serum human complement and polymyxin B, and for the replication of the bacteria within macrophages. The results obtained here highlight functional differences between WzzfepE and Wzzst, although the genes for both proteins are regulated in a PmrA-dependent way.