Combining multiple stressors unexpectedly blocks bacterial migration and growth

Area of Science:

• Microbiology
• Cell Biology
• Biophysics

Background:

• Organisms in nature face multiple stressors simultaneously.
• Laboratory studies often oversimplify conditions by examining single stressors.
• Understanding combined stress effects is crucial for realistic biological insights.

Purpose of the Study:

• To investigate the synergistic effects of simultaneous physical (shear flow) and chemical (hydrogen peroxide) stressors on *Pseudomonas aeruginosa*.
• To re-evaluate hydrogen peroxide (H₂O₂) efficacy under environmentally relevant conditions.
• To identify key molecular responses and mechanisms involved in combined stress tolerance and resistance.

Main Methods:

• Utilized a microfluidic device to apply controlled levels of shear flow and H₂O₂.
• Cultured and treated *Pseudomonas aeruginosa* with combinations of flow and H₂O₂.
• Analyzed bacterial growth, gene regulation (OxyR regulon), scavenging systems, and single-cell behaviors like pilus-driven migration.

Main Results:

• Flow significantly enhances H₂O₂ effectiveness by 50-fold, reducing the concentration needed to inhibit growth.
• Identified the core H₂O₂ regulon and characterized OxyR-mediated dynamic regulation under naturalistic conditions.
• Discovered that combined H₂O₂ and flow block pilus-driven surface migration, impacting bacterial colonization.

Conclusions:

• Laboratory findings using single stressors can significantly overestimate required H₂O₂ concentrations.
• Natural levels of H₂O₂ and flow synergize to restrict bacterial survival and colonization.
• Combined physical and chemical stressors yield unpredictable effects, highlighting the limitations of oversimplified experimental models.