The pH Robustness of Bacterial Sensing.

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Bacteria utilize signal transduction systems with extracytosolic ligand-binding domains (LBDs) for environmental sensing.
• Limited information exists on the pH robustness of bacterial LBDs and their sensing capabilities across varying pH levels.

Purpose of the Study:

• To investigate the pH dependence of ligand recognition by various bacterial LBDs.
• To compare the pH response ranges of periplasmic and cytosolic LBDs.
• To assess the pH robustness of bacterial signaling pathways in vivo.

Main Methods:

• Isothermal titration calorimetry (ITC) to determine pH dependence of ligand binding.
• Analytical ultracentrifugation to analyze LBD dimerization.
• Förster Resonance Energy Transfer (FRET) to measure chemotaxis pathway responses.

Main Results:

• Periplasmic LBDs exhibit broad pH-dependent ligand recognition (over eight pH units), unlike narrower-range cytosolic LBDs.
• The Tar chemoreceptor LBD maintains its dimeric state across tested pH ranges.
• Bacterial motility and chemotaxis show bell-shaped pH dependence centered at pH 7.0.

Conclusions:

• The intrinsic pH resistance of periplasmic LBDs is an evolutionary strategy for bacterial survival in fluctuating environments.
• Extracytosolic sensing robustness facilitates bacterial monitoring of environmental changes.
• Findings will aid in designing robust biosensors for variable pH conditions.