The Legionella pneumophila Incomplete Phosphotransferase System Is Required for Optimal Intracellular Growth and Maximal Expression of PmrA-Regulated Effectors.

The nitrogen phosphotransferase system (PTSNtr) is a regulatory cascade present in many bacteria, where it controls different functions. This system is usually composed of three basic components: enzyme INtr (EINtr), NPr, and EIIANtr (encoded by the ptsP, ptsO, and ptsN genes, respectively). In Legionella pneumophila, as well as in many other Legionella species, the EIIANtr component is missing. However, we found that deletion mutations in both ptsP and ptsO are partially attenuated for intracellular growth. Furthermore, these two PTSNtr components were found to be required for maximal expression of effector-encoding genes regulated by the transcriptional activator PmrA. Genetic analyses which include the construction of single and double deletion mutants and overexpression of wild-type and mutated forms of EINtr, NPr, and PmrA indicated that the PTSNtr components affect the expression of PmrA-regulated genes via PmrA and independently from PmrB and that EINtr and NPr are part of the same cascade and require their conserved histidine residues in order to function. Furthermore, expression of the Legionella micdadei EIINtr component in L. pneumophila resulted in a reduction in the levels of expression of PmrA-regulated genes which was completely dependent on the L. pneumophila PTS components and the L. micdadei EIINtr conserved histidine residue. Moreover, reconstruction of the L. pneumophila PTS in vitro indicated that EINtr is phosphorylated by phosphoenolpyruvate (PEP) and transfers its phosphate to NPr. Our results demonstrate that the L. pneumophila incomplete PTSNtr is functional and involved in the expression of effector-encoding genes regulated by PmrA.