Engineering Bacteria to Harvest Light

Commonly used lab bacteria called E. coli can be converted into light-harvesting organisms in a single genetic step, according to new research from MIT. The genetic enhancement allows microorganisms that normally derive their cellular energy from sugars to switch to a diet of sunlight. These findings could ultimately be used to genetically engineer bacteria that can more efficiently produce biofuels, drugs, and other chemicals.
Some bacteria, such as cyanobacteria, use photosynthesis to make sugars, just as plants do. But others have a newly discovered ability to harvest light through a different mechanism: using light-activated proteins known as proteorhodopsins, which are similar to proteins found in our retinas. When the protein is bound to a light-sensitive molecule called retinal and hit with light, it pumps positively charged protons across the cell membrane. That creates an electrical gradient that acts as a source of energy, much like the voltage, or electromotive force, supplied by batteries.

First discovered in marine organisms in 2000, scientists recently found that the genes for the proteorhodopsin system–essentially a genetic module that includes the genes that code for both the protein and the enzymes required to produce retinal–are frequently swapped among different microorganisms in the ocean. (While we usually think of genes being passed from parent to offspring, microorganisms can exchange bits of DNA laterally.)

Intrigued by the prospect that a single piece of DNA is really all an organism needs to harvest energy from light, the researchers inserted it into E. coli. They found that the microorganisms synthesized all the necessary components and assembled them in the cell membrane, using the system to generate energy. “All it takes to derive energy from sunlight is that bit of DNA,” saysEd Delong, professor of biological engineering at MIT and author of the study. The results were published last week in the Proceedings of the National Academy of Sciences.

Technology Review