The Francisella tularensis migR,trmE, andcphAGenes Contribute to F. tularensis Pathogenicity Island Gene Regulation and Intracellular Growth by Modulation of the Stress Alarmone ppGpp

Abstract

ABSTRACTTheFrancisella tularensispathogenicity island (FPI) encodes many proteins that are required for virulence. Expression of these genes depends upon the FevR (PigR) regulator and its interactions with the MglA/SspA and RNA polymerase transcriptional complex. Experiments to identify how transcription of the FPI genes is activated have led to identification of mutations within themigR,trmE, andcphAgenes that decrease FPI expression. Recent data demonstrated that the small alarmone ppGpp, produced by RelA and SpoT, is important for stabilizing MglA/SspA and FevR (PigR) interactions inFrancisella. Production of ppGpp is commonly known to be activated by cellular and nutritional stress in bacteria, which indicates that cellular and nutritional stresses act as important signals for FPI activation. In this work, we demonstrate that mutations inmigR,trmE, orcphAsignificantly reduce ppGpp accumulation. The reduction in ppGpp levels was similar for each of the mutants and correlated with a corresponding reduction iniglAreporter expression. In addition, we observed that there were differences in the ability of each of these mutants to replicate within various mammalian cells, indicating that themigR,trmE, andcphAgenes are likely parts of different cellular stress response pathways inFrancisella. These results also indicate that different nutritional and cellular stresses exist in different mammalian cells. This work provides new information to help understand howFrancisellaregulates its virulence genes in response to host cell environments, and it contributes to our growing knowledge of this highly successful bacterial pathogen.