Abstract
Francisella tularensis is an intracellular bacterium and as such is expected to encounter a continuous attack by reactive oxygen species (ROS) in its intracellular habitat and efficiently coping with oxidative stress is therefore essential for its survival. The oxidative stress response system of F. tularensis is complex and includes multiple antioxidant enzymes and pathways, including the transcriptional regulator OxyR and the H2O2-decomposing enzyme catalase, encoded by katG. The latter is regulated by OxyR. A deletion of either of these genes, however, does not severely compromise the virulence of F. tularensis and we hypothesized that if the bacterium would be deficient of both catalase and OxyR, then the oxidative defense and virulence of F. tularensis would become severely hampered. To test this hypothesis, we generated a double deletion mutant, ΔoxyR/ΔkatG, of F. tularensis LVS and compared its phenotype to the parental LVS strain and the corresponding single deletion mutants. In accordance with the hypothesis, ΔoxyR/ΔkatG was distinctly more susceptible than ΔoxyR and ΔkatG to H2O2, ONOO−, and , moreover, it hardly grew in mouse-derived BMDM or in mice, whereas ΔkatG and ΔoxyR grew as well as F. tularensis LVS in BMDM and exhibited only slight attenuation in mice. Altogether, the results demonstrate the importance of catalase and OxyR for a robust oxidative stress defense system and that they act cooperatively. The lack of both functions render F. tularensis severely crippled to handle oxidative stress and also much attenuated for intracellular growth and virulence.
Highlights
Francisella tularensis, a Tier 1 select agent and the causative agent of tularemia, is a zoonotic, facultative intracellular bacterium with two clinically relevent subspecies, tularensis and holarctica, the former of which causes an aggressive disease with high mortality if left untreated (Oyston et al, 2004)
There are several reactive oxygen species (ROS) with potent antibacterial effects, such as superoxide and H2O2. The former is produced at high levels by the phagocyte oxidase and it rapidly combines with nitric oxide (NO), which is produced at high levels by inducible nitric oxide synthase, to form peroxynitrite, a highly reactive compound
To explore if a reduced oxygen tension could rescue the growth of oxyR/ katG, the strains were cultivated under microaerobic conditions, i.e., 10% O2 and
Summary
Francisella tularensis, a Tier 1 select agent and the causative agent of tularemia, is a zoonotic, facultative intracellular bacterium with two clinically relevent subspecies, tularensis and holarctica, the former of which causes an aggressive disease with high mortality if left untreated (Oyston et al, 2004). Phagocytes constitute a hostile environment utilizing a wide array of anti-bacterial mechanisms, such as phagosome acidification, disruption of pathogen membrane integrity, removal or sequestration of nutrients, and the production of reactive oxygen species (ROS) (Flannagan et al, 2009) and since F. tularensis is an intracellular bacterium, it will encounter a continuous exposure to ROS. Vital macromolecules, such as proteins and DNA, will react with ROS, thereby disrupting their functions (Fridovich, 1998; Schaible and Kaufmann, 2004; Flannagan et al, 2009). H2O2 is toxic per se, but the damage it exerts can be exacerbated in combination with intracellular ferrous iron, resulting in the formation of hydroxyl radicals (HO) and hydroxide anions (OH−) through the Fenton reaction
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
