December 12, 2019
Israeli scientists have revealed a potential weapon in the battles against air pollution, deforestation and climate change: bacteria engineered to eat carbon dioxide (CO2) from the environment.
Prof. Ron Milo's plant and environmental sciences research lab at the Weizmann Institute of Science published a report on the study in Cell on November 27.
Milo's team spent nearly a decade using rational design, genetic engineering and a sped-up version of evolution to create unique CO2-eating E. coli bacteria.
First, they identified the genes that plants use for the process of carbon fixation — taking carbon from CO2 and turning it into protein, DNA and other biological molecules. Many of these genes were already present in the bacteria. Others could be added or modified.
They also inserted a gene that allows bacteria to get energy from formate, a readily available substance that can be produced directly from electricity and air.
Once the cultured bacteria had the necessary genetic mechanics, they still had to be coaxed into making the switch from their normal food (sugar) to CO2.
Postdoctoral fellow Shmuel Gleizer, the lead researcher, did this with a technique called lab evolution.
Together with PhD students Roee Ben-Nissan, Yinon Bar-On and other members of Milo's team, Gleizer weaned the bacteria gradually off the sugar they were used to eating.
At each stage, cultured bacteria were given just enough sugar to keep them from complete starvation, as well as plenty of CO2 and formate.
Subsequent generations of the original cultured bacteria were given less and less sugar. After about a year of adapting to the new diet, some of them did switch to living and multiplying in an environment of pure CO2.
The researchers even used a special method to make sure the E. coli weren't "snacking" on other nutrients.
Researchers converted sugar-eating E. coli bacterium (left) to producing all of its biomass from CO2, using metabolic engineering combined with lab evolution. The new bacterium (center) uses the compound formate as a form of chemical energy to drive CO2 fixation. The bacterium may provide the infrastructure for renewable production of food and green fuels (right). (Chart courtesy of the Weizmann Institute)
Cultured bacteria for a healthier planet
"Our lab was the first to pursue the idea of changing the diet of a normal heterotroph (one that eats organic substances) to convert it to autotrophism ('living on air')," said Milo.
"It sounded impossible at first, but it has taught us numerous lessons along the way, and in the end we showed it indeed can be done. Our findings are a significant milestone toward our goal of efficient, green scientific applications."
The researchers believe that the cultured bacteria could prove healthy for the planet in a variety of ways.
"There are several scenarios in which this current research could be potentially applied in the future to address climate change," Bar-On tells ISRAEL21c.
"Engineering an E. coli strain capable of utilizing energy sources such as formate, which could be synthesized electrochemically from renewable energy, opens the possibility of producing net-zero emissions ethanol, butanol, and potentially even denser fuels such as diesel fuels, which could replace fossil fuels," says Bar-On.
Industrial renewable food production
In addition, the research could serve as the basis for future methods to increase food production without the vast land masses currently needed for raising meat and vegetables.
"Reducing the land demand of food production can help to reduce the greenhouse gas emissions associated with agriculture, for example by reducing the amount of deforestation," Bar-On explains.
Biotech companies that currently feed large amounts of corn syrup to bacteria or yeast to produce commodity chemicals could instead use cultured bacteria that live on a diet of CO2 and renewable electricity. That's another potential way to reduce land demand.
The CO2-eating bacteria also could be useful in producing alternative protein, a major goal in the food-tech world.
"In the future, we may be able to use renewable energy to drive carbon fixation and protein production in such bacteria," says Bar-On. "This process can be scaled up to produce protein from renewable sources, which could serve as the feedstock of livestock, for example."
Because E. coli are "the powerhouse of molecular biology research," says Bar-On, cultured E.coli that live on air alone will allow researchers "to probe much closer the components of the carbon fixation machinery, which also operates in all of the plants providing our food.
"As such, this bacterium could serve as a stepping-stone for discoveries that may improve the process of carbon fixation and could someday be implemented in crops to increase food production."