Light-powering Escherichia coli with proteorhodopsin. Proc Nat Acad Sci

Department of Molecular and Cell Biology , University of California, Berkeley, Berkeley, California, United States
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 03/2007; 104(7):2408-12. DOI: 10.1073/pnas.0611035104
Source: PubMed


Proteorhodopsin (PR) is a light-powered proton pump identified by community sequencing of ocean samples. Previous studies have established the ecological distribution and enzymatic activity of PR, but its role in powering cells and participation in ocean energy fluxes remains unclear. Here, we show that when cellular respiration is inhibited by depleting oxygen or by the respiratory poison azide, Escherichia coli cells expressing PR become light-powered. Illumination of these cells with light coinciding with PR's absorption spectrum creates a proton motive force (pmf) that turns the flagellar motor, yielding cells that swim when illuminated with green light. By measuring the pmf of individual illuminated cells, we quantify the coupling between light-driven and respiratory proton currents, estimate the Michaelis-Menten constant (Km) of PR (10(3) photons per second/nm2), and show that light-driven pumping by PR can fully replace respiration as a cellular energy source in some environmental conditions. Moreover, sunlight-illuminated PR+ cells are less sensitive to azide than PR- cells, consistent with PR+ cells possessing an alternative means of maintaining cellular pmf and, thus, viability. Proteorhodopsin allows Escherichia coli cells to withstand environmental respiration challenges by harvesting light energy.

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    • "In heterotrophic bacteria, the physiological functions suggested for PR include enhanced survival or growth under starvation conditions (Lami et al., 2009; Gómez-Consarnau et al., 2010; Steindler et al., 2011; Akram et al., 2013) and powering of cell motility (Walter et al., 2007), among others (Fuhrman et al., 2008). Along these lines, PR in cyanobacteria might play a role in nutrient acquisition when photosynthetic activities are limited by bioavailable nutrients such as nitrogen (Van Mooy and Devol, 2008) or iron (Mann and Chisholm, 2000). "
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    • "AND4, another PR-containing strain, exhibited longer survival during starvation than its corresponding PR deletion mutant (Gomez-Consarnau et al. 2010). When expressed in E. coli, a PR from the SAR-86 clade of the Gammaproteobacteria promotes proton-motive force that turns the flagellar motor during light illumination (Walter et al. 2007). Several lines of evidence suggest that the PR in DSW-6 should be a functional equivalent of other PRs and may play similar roles to contribute to the growth or survival of the bacterium in oligotrophic environments. "
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