Transcription Factors DksA and PsrA are synergistic contributors toL. pneumophilavirulence inAcathamoeba castellaniiprotozoa

Abstract

AbstractThe environmental bacteriumLegionella pneumophila, an intracellular parasite of free-living freshwater protozoa as well as an opportunistic human pathogen, has a biphasic lifestyle. The switch from the vegetative replicative form to the environmentally resilient transmissive phase form is governed by a complex stringent response-based regulatory network that includes RNA polymerase co-factor DksA. Here we report that, through a dysfunctional DksA mutation (DksA1), a synergistic interplay was discovered between DksA and transcription regulator PsrA. InAcanthamoeba castellaniiprotozoa, the presence of DksA1 ensured optimal intracellular growth, whereas PsrA could partially rescue the growth defect of thedksA1strain. Conversely, overproduction of DksA rescued the growth defect of a ΔpsrAstrain. Observedin vitro; either DksA or DksA1 were required for extended culturability of bacterial cells in depleted broth, but normal cell morphology and pigmentation required DksA only. Comparative structural modeling predicts that the DksA1 mutation affects coordination of Mg2+into the active site of RNAP compromising transcription efficiency. Taken together, we propose that PsrA transcriptionally assists DksA. Additionally,in vitroevidence suggests that the long chain fatty chain metabolic response is mediated by PsrA together with DksA inferring a novel regulatory link to the stringent response pathway.