Lecture Notes: The Stringent Response Controls Catalases in Pseudomonas aeruginosa

Abstract

• Pseudomonas aeruginosa is a human opportunistic pathogen.
• It has antioxidant defense enzymes controlled by multiple regulatory systems.
• Inactivation of the stringent response (SR) impairs antioxidant defenses and antibiotic tolerance.
• Catalases are key antioxidant enzymes.
• SR is required for optimal catalase activity and H2O2 tolerance.
• Upregulation of catalase activity occurs upon amino acid starvation.
• katA and katB expression requires SR regulation.
• Overexpression of katA restores H2O2 tolerance and partially rescues antibiotic tolerance.

Introduction

• Reactive oxygen species (ROS) are produced during aerobic respiration and by host phagocytic cells during infections.
• Bacteria have antioxidant defenses to survive aerobic growth and in vivo conditions.
• Nutrient limitation can elicit antioxidant responses.
• The stringent response (SR) is a regulatory mechanism mediated by the alarmone (p)ppGpp.
• P. aeruginosa uses catalases to detoxify H2O2.
• katA is constitutively expressed and dominant during exponential/stationary phases.
• katB is induced by H2O2 stress.
• SR inactivation decreases antibiotic tolerance and is linked to oxidative-stress pathways.

Materials and Methods

• Growth Conditions: Different media (LB, M9) and conditions (planktonic, biofilm) were used.
• Bacterial Strains: Various strains and mutants were used, including SR and RpoS mutants.
• Plasmids and Vector Construction: Standard molecular methods and specific plasmid constructions were employed.
• H2O2 and Antibiotic Challenges: Methods for testing susceptibility and tolerance were outlined.
• Catalase Activity and ROS Measurement: Assays performed to measure catalase activity and ROS levels.

Results

Susceptibility to H2O2

• SR mutant is more susceptible to H2O2.
• Biofilms show increased oxidant killing when SR is inactive.

Catalase Activity

• SR is crucial for full catalase activity in planktonic and biofilm growth.

Role of (p)ppGpp

• SR and (p)ppGpp signaling induce catalase activity during starvation.

Intracellular ROS

• SR inactivation increases endogenous ROS levels.

RpoS and H2O2 Tolerance

• RpoS is significant for H2O2 resistance.
• SR affects catalase activity and H2O2 tolerance through RpoS-dependent and independent mechanisms.

Gene Expression

• SR regulates katA and katB transcription.
• katA expression is growth-phase dependent, while katB is H2O2-induced.

KatA Overexpression

• Restores H2O2 tolerance and partially rescues antibiotic tolerance in SR mutants.

Discussion

• Nutrient limitation induces oxidative stress tolerance.
• SR regulates catalase activity and expression.
• RpoS and quorum sensing are intermediary regulators.
• SR influences H2O2 and antibiotic tolerance by balancing prooxidant stress and antioxidant defenses.

Proposed Model

• SR mediates antibiotic tolerance through regulation of catalases and HAQ molecules.

Acknowledgments

• Funding and support from various institutions and individuals are acknowledged.

References

• Extensive references to previous research and studies are provided throughout the text.