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Light-powering Escherichia coli with proteorhodopsin
Jessica M Walter1, Derek Greenfield, Carlos Bustamante
1Department of Physics, University of California, Berkeley, CA 94720, USA.
Summary
Proteorhodopsin (PR) allows Escherichia coli to use light for energy when respiration fails. This light-powered proton pump generates a proton motive force, enabling cell motility and survival in challenging environments.
Area of Science:
- Microbiology
- Biochemistry
- Oceanography
Background:
- Proteorhodopsin (PR) is a light-powered proton pump found in marine environments.
- Its ecological distribution and enzymatic activity are known, but its role in cellular energy production and ocean energy flux is unclear.
Purpose of the Study:
- To investigate the role of proteorhodopsin in powering cells under conditions of inhibited respiration.
- To quantify the energy coupling between light-driven and respiratory proton currents.
Main Methods:
- Escherichia coli cells expressing PR were subjected to inhibited respiration (low oxygen or azide).
- Cellular proton motive force (pmf) was measured under illumination.
- PR's Michaelis-Menten constant (Km) was estimated.
Main Results:
- Illuminated PR-expressing E. coli generated pmf, drove flagellar motors, and swam.
- Light-driven proton pumping by PR could fully substitute for respiration.
- PR-expressing cells showed increased resistance to azide, indicating maintained pmf and viability.
Conclusions:
- Proteorhodopsin enables Escherichia coli to harvest light energy, providing an alternative power source when respiration is compromised.
- PR enhances cellular viability by maintaining pmf under environmental stress.
- This finding highlights PR's significant contribution to cellular energy metabolism and survival in marine ecosystems.
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