Bacteria Made to Harvest Light
A set of genes found in marine microörganisms can give common bacteria the ability to generate energy from light

Source: “Proteorhodopsin ­Photo­system Gene Expression ­Enables Photophosphorylation in a ­Heterologous Host”
Edward F. DeLong et al.
Proceedings of the National Academy of Sciences 104(13): 5590-5595

Results: The common bacterium E. coli can be converted into a light-­harvesting organism in a single genetic step. MIT researchers modified the E. coli genome to include a string of DNA found in marine microörganisms that can generate energy from light. The resulting bacteria synthesized all the components necessary to duplicate that feat and assembled them in the cell membrane.

Why it matters: The genetically modified E. coli, which would normally derive their energy from organic compounds like sugars, were able to switch to a diet of sunlight. Similar modifications could lead to bacteria that more efficiently produce biofuels, drugs, and other chemicals, since they could use more of their carbon food sources as material for bioproducts rather than “burning” them for energy.

The findings also shed light on microbial evolution. Scientists had previously found that the genes for the light-harvesting system, which are often found grouped together in the genome, are frequently swapped among different microörganisms in the ocean. The fact that a single genetic transfer can provide cells with all the genes they need to harvest energy from light helps explain how that capacity could travel so widely. (The mechanism for converting light into energy described here, which was discovered just a few years ago, is different from chlorophyll-based photosynthesis.)

Methods: The genes inserted into the E. coli enabled them to synthesize two proteins: proteo­rhodopsin, which is similar to a protein found in the human retina, and retinal, a light-­sensitive molecule that binds to proteo­rhodopsin. When the proteo­rhodopsin is bound to retinal and struck with light, it pumps positively charged protons across the cell membrane. That creates an electrical gradient that acts as a source of energy.

Next Steps: The researchers are now working on ways to boost the modified bacteria’s ability to harvest and use energy from light.