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Background: The opportunistic bacterial pathogen Legionella pneumophila uses substrate effectors of Dot/Icm type IVB secretion system (T4BSS) to accomplish survival and replication in amoebae cells and mammalian alveolar macrophages. During the conversion between its highly resistant, infectious dormant form and vigorously growing, uninfectious replicative form, L. pneumophila utilizes a complicated regulatory network in which proteolysis may play a significant role. As a highly conserved core protease, ClpP is involved in various cellular processes as well as virulence in bacteria, and has been proved to be required for the expression of transmission traits and cell division of L. pneumophila. Results: The clpP-deficient L. pneumophila strain failed to replicate and was digested in the first 3 h post-infection in mammalian cells J774A.1. Further investigation demonstrates that the clpP deficient mutant strain was unable to escape the endosome-lysosomal pathway in host cells. We also found that the clpP deficient mutant strain still expresses T4BSS components, induces contact-dependent cytotoxicity and translocate effector proteins RalF and LegK2, indicating that its T4BSS was overall functional. Interestingly, we further found that the translocation of several effector proteins is significantly reduced without ClpP. Conclusions: The data indicate that ClpP plays an important role in regulating the virulence and effector translocation of Legionella pneumophila. [ABSTRACT FROM AUTHOR]

Background: Legionella pneumophila, the intracellular bacterial pathogen that causes Legionnaires' disease, exhibit characteristic transmission traits such as elevated stress tolerance, shortened length and virulence during the transition from the replication phase to the transmission phase. ClpP, the catalytic core of the Clp proteolyticcomplex, is widely involved in many cellular processes via the regulation of intracellular protein quality.Results: In this study, we showed that ClpP was required for optimal growth of L. pneumophila at high temperatures and under several other stress conditions. We also observed that cells devoid of clpP exhibited cellelongation, incomplete cell division and compromised colony formation. Furthermore, we found that the clpPdeletedmutant was more resistant to sodium stress and failed to proliferate in the amoebae host Acanthamoebacastellanii. Conclusions: The data present in this study illustrate that the ClpP protease homologue plays an important role inthe expression of transmission traits and cell division of L. pneumophila, and further suggest a putative role of ClpPin virulence regulation. [ABSTRACT FROM AUTHOR]