Combining multiple stressors blocks bacterial migration and growth.

Area of Science:

• Microbiology
• Biophysics
• Pathogen Research

Background:

• Organisms in nature encounter multiple stressors simultaneously.
• Laboratory studies often simplify conditions, focusing on single stressors and population-level responses.
• Microfluidic techniques allow for single-cell resolution of bacterial stress responses.

Purpose of the Study:

• To investigate the combined effects of physical (shear flow) and chemical (hydrogen peroxide, H₂O₂) stressors on Pseudomonas aeruginosa.
• To determine if naturally occurring levels of these stressors impact bacterial growth and behavior.
• To re-evaluate previously reported H₂O₂ concentrations required to inhibit bacterial growth under more realistic conditions.

Main Methods:

• Utilized a microfluidic system to apply simultaneous shear flow and H₂O₂ exposure to Pseudomonas aeruginosa.
• Quantified bacterial growth and survival under combined stress conditions relevant to human host tissues.
• Analyzed single-cell behavior, including surface migration and gene regulation.

Main Results:

• Flow was found to increase the effectiveness of H₂O₂ by 50-fold, reducing the required concentration for growth inhibition.
• Identified the core H₂O₂ regulon and characterized OxyR-mediated regulation at natural H₂O₂ levels.
• Observed that combined H₂O₂ and flow synergistically inhibit pilus-driven surface migration, impacting bacterial motility and survival.

Conclusions:

• Laboratory studies overestimating H₂O₂ toxicity due to the absence of physical flow.
• Natural levels of H₂O₂ and flow synergize to restrict bacterial motility and survival.
• Combined stressors can lead to unpredictable effects, highlighting the limitations of simplified experimental models.