Dynamic velocity response of E. coli powered by proteorhodopsin

Area of Science:

• Microbiology
• Biophysics
• Cellular Biophysics

Background:

• Bacterial swimming motility relies on flagellar motors, powered by proton flux.
• Proton motive force (PMF) drives these motors, often modeled as a simple electrical circuit.
• The precise dynamics of proton flow and its dissipation remain incompletely understood.

Purpose of the Study:

• To investigate the dynamical response of bacterial proton motive force under tunable optical driving.
• To test the validity of simplified circuit models for describing proton flux in E. coli.
• To identify the primary sinks for proton motive force discharge and characterize their resistive behavior.

Main Methods:

• Utilized a light-driven outward proton pump (proteorhodopsin) in E. coli.
• Monitored bacterial swimming activity under controlled optical illumination.
• Applied tunable optical driving to probe system dynamics and proton current.

Main Results:

• Flagellar motors are not the dominant pathway for proton motive force discharge.
• Other membrane channels carry a larger proton current than flagellar motors.
• These alternative membrane channels exhibit nonlinear resistive properties.

Conclusions:

• The simple circuit model for proton motive force dissipation is insufficient.
• Non-flagellar membrane channels play a critical role in proton current dynamics.
• Direct quantification of proteorhodopsin activity provides insights into light-driven proton pumping.