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

Department of Physics, University of California, Berkeley, CA 94720, USA.
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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    ABSTRACT: Uncovering the metabolic capabilities of microbes is key to understanding global energy flux and nutrient transformations. Since the vast majority of environmental microorganisms are uncultured, metagenomics has become an important tool to genotype the microbial community. This study uses a recently developed computational method to confidently assign metagenomic reads to microbial clades without the requirement of metagenome assembly by comparing the evolutionary pattern of nucleotide sequences at non-synonymous sites between metagenomic and orthologous reference genes. We found evidence for new, ecologically relevant metabolic pathways in several lineages of surface ocean bacterioplankton using the Global Ocean Survey (GOS) metagenomic data, including assimilatory sulfate reduction and alkaline phosphatase capabilities in the alphaproteobacterial SAR11 clade, and proteorhodopsin-like genes in the cyanobacterial genus Prochlorococcus. These findings raise new hypotheses about microbial roles in energy flux and organic matter transformation in the ocean.
    Environmental Microbiology Reports 10/2013; 5(5):686-696. DOI:10.1111/1758-2229.12068 · 3.29 Impact Factor
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    • "A wide variety of metabolic engineering and systems biology approaches, including synthetic biology with microorganisms, has been made for exploitation of diverse biomass resources (Walter et al., 2007; Rude and Schirmer, 2009; Oh et al., 2011; Zhang et al., 2011). Although these approaches are promising, there are still limitations in terms of the technical feasibility of cost-effective energy resources and the availability of rapid genetic tools and in-depth physiological knowledge for the effective manipulation of energy transduction systems. "
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    ABSTRACT: The finite reservation of fossil fuels accelerates the necessity of development of renewable energy sources. Recent advances in synthetic biology encompassing systems biology and metabolic engineering enable us to engineer and/or create tailor made microorganisms to produce alternative biofuels for the future bio-era. For the efficient transformation of biomass to bioenergy, microbial cells need to be designed and engineered to maximize the performance of cellular metabolisms for the production of biofuels during energy flow. Toward this end, two different conceptual approaches have been applied for the development of platform cell factories: forward minimization and reverse engineering. From the context of naturally minimized genomes,non-essential energy-consuming pathways and/or related gene clusters could be progressively deleted to optimize cellular energy status for bioenergy production. Alternatively, incorporation of non-indigenous parts and/or modules including biomass-degrading enzymes, carbon uptake transporters, photosynthesis, CO2 fixation, and etc. into chassis microorganisms allows the platform cells to gain novel metabolic functions for bioenergy. This review focuses on the current progress in synthetic biology-aided pathway engineering in microbial cells and discusses its impact on the production of sustainable bioenergy.
    Frontiers in Microbiology 04/2013; 4:92. DOI:10.3389/fmicb.2013.00092 · 3.99 Impact Factor
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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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    ABSTRACT: Rhodopsin-containing marine microbes such as those in the class Flavobacteria play a pivotal role in the biogeochemical cycle of the euphotic zone . Deciphering the genome information of flavobacteria and accessing the diversity and ecological impact of microbial rhodopsins is important in understanding and preserving the global ecosystems. The genome sequence of the orange-pigmented marine flavobacterium Nonlabens dokdonensis (basonym: Donghaeana dokdonensis) DSW-6 was determined. As a marine photoheterotroph, DSW-6 has written in its genome physiological features that allow survival in marine oligotrophic environments. The sequence analysis also uncovered a gene encoding an unexpected type of microbial rhodopsin containing a unique motif in addition to a proteorhodopsin gene and a number of photolyase or cryptochrome genes. Homologs of the novel rhodopsin gene were found in other flavobacteria, alphaproteobacteria, a species of cytophaga, a deinococcus, and even a eukaryote diatom. They all contain the characteristic NQ motif and form a phylogenetically distinct group. Expression analysis of this rhodopsin gene in DSW-6 indicated that it is induced at high NaCl concentrations, as well as in the presence of light and the absence of nutrients. Genomic and metagenomic surveys demonstrate the diversity of the NQ rhodopsins in nature and the prevalent occurrence of the encoding genes among microbial communities inhabiting hypersaline niches, suggesting its involvement in sodium metabolism and the sodium-adapted lifestyle.
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