Francisella tularensis is a Gram-negative bacterium responsible for causing
tularemia in the northern hemisphere. F. tularensis has long been developed as a
biological weapon due to its ability to cause severe illness upon inhalation of as few as ten organisms and, based on its potential to be used as a bioterror agent is now classified as a Tier 1 Category A select agent by the CDC. The stringent response facilitates bacterial survival under nutritionally challenging
starvation conditions. The hallmark of stringent response is the accumulation of the effector molecules
ppGpp and (
p)ppGpp known as stress alarmones. The relA and spoT gene products generate alarmones in several Gram-negative bacterial pathogens. RelA is a ribosome-associated
ppGpp synthetase that gets activated under
amino acid starvation conditions whereas, SpoT is a bifunctional
enzyme with both
ppGpp synthetase and
ppGpp hydrolase activities. Francisella encodes a monofunctional RelA and a bifunctional SpoT
enzyme. Previous studies have demonstrated that stringent response under nutritional stresses increases expression of virulence-associated genes encoded on Francisella Pathogenicity Island. This study investigated how stringent response governs the oxidative stress response of F. tularensis. We demonstrate that RelA/SpoT-mediated
ppGpp production alters global gene transcriptional profile of F. tularensis in the presence of oxidative stress. The lack of stringent response in relA/spoT gene deletion mutants of F. tularensis makes bacteria more susceptible to
oxidants, attenuates survival in macrophages, and virulence in mice. This work is an important step forward towards understanding the complex regulatory network underlying the oxidative stress response of F. tularensis.