Stringent response governs the oxidative stress resistance and virulence of Francisella tularensis

Abstract

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.

Proteome Expression and Survival Strategies of a Proteorhodopsin-ContainingVibrioStrain under Carbon and Nitrogen Limitation

“…S4 ) confirm that both C- and N-limited cultures engage stringent-response transcriptional programs by stationary phase. While the effects of the stringent response in the N-limited cells are less clear, we observed in stationary phase a higher proteomic expression of stringent response protein A (SspA), a stringent response transcription factor which has previously been linked to amino acid starvation, acid resistance, and virulence ( 61 – 64 ). Together, these observations suggest that the stringent responses in Vibrio campbellii to carbon limitation and nitrogen starvation differ and cause distinct downstream effects on gene expression.…”

Enhanced stress resistance of Bifidobacterium breve NRBB57 by induction of stress proteins at near-zero growth rates

“…In addition to previously proposed roles for transcriptional regulators in B. breve UCC2003 that activate stress defence in selected stress conditions conceivably by loss of repressor function (Zomer et al, 2009;Zomer and Van Sinderen, 2010), our current study provides evidence for activation of a multiplicity of stress defence proteins in retentostat cells at near-zero growth rates, conceivably linked to the induction of the stringent response in B. breve NRBB57 under these extreme nutrient-limited conditions (Ortiz Camargo et al, 2022). The stringent response is known to be induced by nutrient deprivation, and is mediated by the alarmones guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp) (Irving et al, 2021), and (indirectly) controls expression of stress defence proteins, such as DnaK, GroESL, and ClpB (Carneiro et al, 2011;Schäfer et al, 2020), and oxidative stress response proteins such as thioredoxin and glutaredoxin (Khakimova et al, 2013;Ma et al, 2019). Activation of genes involved in stringent response was described for a range of bacteria including acid-stressed B. longum (Jin et al, 2012;Schell et al, 2002).…”

Metazoan stringent-like response mediated by MESH1 phenotypic conservation via distinct mechanisms

“…Iron starvation can activate the stringent response in Bacillus Subtilis and E. coli [24] , [25] . Additionally, oxidative stresses can activate the stringent response in Francisella tularensis and Staphylococcus aureus and the removal of the alarmone makes the bacterial cells more susceptible to oxidative stresses such as H 2 O 2 [26] , [27] . The bacterial stringent response alters the expression of antioxidant defense mechanisms.…”