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

The nitrogen phosphotransferase system (PTS) is a regulatory cascade present in many bacteria, where it controls different functions. This system is usually composed of three basic components: enzyme I (EI), NPr, and EIIA (encoded by the , , and genes, respectively). In , as well as in many other species, the EIIA component is missing. However, we found that deletion mutations in both and are partially attenuated for intracellular growth. Furthermore, these two PTS 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 EI, NPr, and PmrA indicated that the PTS components affect the expression of PmrA-regulated genes via PmrA and independently from PmrB and that EI and NPr are part of the same cascade and require their conserved histidine residues in order to function. Furthermore, expression of the EII component in resulted in a reduction in the levels of expression of PmrA-regulated genes which was completely dependent on the PTS components and the EII conserved histidine residue. Moreover, reconstruction of the PTS indicated that EI is phosphorylated by phosphoenolpyruvate (PEP) and transfers its phosphate to NPr. Our results demonstrate that the incomplete PTS is functional and involved in the expression of effector-encoding genes regulated by PmrA.