In Breakthrough, Israeli Researchers Feed CO2 to Bacteria to Curb Greenhouse Gasses

Weizmann Institute scientists wean bacteria off of sugar, possibly leading the way to producing 'green fuel'

Prof. Ron Milo, left and Dr. Shmuel Gleizer at the Weizmann Institute in Rehovot, November 27, 2019.
Ilan Assayag

The human race is now facing some of the greatest challenges in its history. One of these is how to ensure there will be enough food and energy for some 8 billion people in the midst of the growing climate crisis. This crisis raises doubts about the ability of humanity to continue reproducing while also improving quality of life, or even maintaining it at its current level, and of course, preventing a catastrophe that will harm millions of lives.

Whether humanity can successfully meet this challenge – and how – are still open questions. But all the experts realize that to do so, we’ll first have to wean ourselves from dependence on fossil fuel, which, when burned, raises the concentration of carbon dioxide in the atmosphere, increases the greenhouse effect and leads to destructive global warming. To reduce our dependence on oil, coal and gas, clearly there will have to be changes in lifestyle, but there is also hope that scientists will be able to move us toward the production of renewable sources of energy, whose cost to the environment is much lower.

A new study at the Weizmann Institute of Science in Rehovot has presented a breakthrough in production of a fuel whose environmental cost is low. Scientists there have managed to wean bacteria off of sugar and feed them only on carbon dioxide in the air around them, in a combination of genetic engineering and directed evolution of the microscopic creatures.

The research presenting this achievement was published Wednesday in the scientific journal Cell.

Prof. Ron Milo, of Weizmann’s Department of Plant and Environmental Sciences, in whose laboratory the research was carried out, explains that all organisms in nature are either “producers” or “consumers” of sugar and other foods, such as fats. The producers are algae, plants and a few kinds of bacteria living in extreme environments. These bacteria draw carbon dioxide from their environment and with the help of the sun’s energy, they fix it and create a complex molecule – like sugars – that are essential for life.

The rest of the organisms exist on the work of those plants and algae and are nourished by them – thus receiving the sugars they need to exist. In scientific terms, the “producers” are called “autotrophs” and the consumers heterotrophs. In Prof. Milo’s lab, the team worked for 10 years until they managed to turn a heteotrophic bacterium into an autotroph – from a consumer to a producer.

In the first stage, the researchers, headed by Dr. Shmuel Gleizer, took ordinary E. coli bacteria that are frequently used in industry and research labs. E. coli is an ordinary heterotrophic bacterium that requires sugars to produce energy and the building materials needed for the cell, known as biomass.

Then, with the help of a genetic editing tool, they attached to the bacteria’s genes essential for carbon fixing. These genes came from another bacterium, known as cyanobacteria, which is a microorganism that lives in water and can carry out photosynthesis. They also added another gene to the bacteria that allowed it to receive energy from a material called formate as a substitute for energy from the sun in photosynthesis.

This genetic editing was not enough to wean the bacteria off of sugar, and so Dr. Gleizer, along with research students Roi Ben-Nissan and Yinon Bar-On and others, began to wean the cultures off of sugar. They fed the bacteria on carbon dioxide and formate, along with tiny amounts of sugar, in a months-long process of directed evolution. They then gradually reduced the amount of sugar the bacteria that survived received. Six months later later, some of the first descendants of the bacteria managed to survive, flourish and reproduce with no sugar at all.

At the next stage, the scientists focused on proving that the upgraded bacteria were surviving only on carbon dioxide. To do so, they used air with “enriched carbon”: a combination of gasses containing the isotope carbon 13, which can be differentiated from other isotopes.

Prof. Ron Milo and Dr. Shmuel Gleizer.
Ilan Assayag

The researchers fed the bacteria with air containing carbon dioxide with the isotope carbon 13, which is different from the more common carbon 12. They then examined the biomass of the bacteria that developed nourished in this way, and saw that indeed the carbon atoms in their bodies were carbon 13 originating in the air the bacteria consumed and not from other sources.

Milo said that for now, "we have managed to prove a far-reaching change can be made," stressting that "it wasn't clear" up until now whether such a breakthrough was possible at all. The next phase of the research, according to Milo, is to improve the efficiency of the carbon fixing process. At the moment the bacteria need air with a 5-percent concentration of carbon dioxide, more than 100 times the concentration in the atmosphere.

The scientists hope to develop a closed cycle of the creation of a biofuel: The formate that charges the bacteria cells with the energy needed to fix the carbon can be produced directly from the air with solar energy or other renewable energy. This material will serve the bacteria in fixing carbon dioxide from the atmosphere and grow, and biofuel can be created from the biomass. The use of this biofuel does not contribute to the greenhouse effect, because all the carbon dioxide emitted when it is burned comes from the atmosphere.

According to Milo, the goal now is to continue to use formate as a source of outside energy and not try to induce the bacteria to photosynthesize directly from the sun’s energy. However, “even what we have shown so far is considered by many to be unrealistic, and so it is possible that this milestone will also be crossed,” he says. Possible additional uses of the upgraded bacteria developed in the lab is to filter carbon dioxide produced by industries.

Milo says the bacteria are still unable to survive on their own, and so they do not intent to scatter them directly in the environment to actively reduce the rate of greenhouse gasses in the atmosphere. Beyond the infeasibility of releasing the bacteria, Milo explains that such direct intervention in nature carries too many risks. But another direction of the research could help improve agricultural output: Experiments on carbon fixing in bacteria also reveal new information about the way carbon is fixed in nature. The insights that arise from this can help scientists improve photosynthesis of crops so as to increase production in the field.