Bacteria that feed on carbon dioxide only and build the entire biomass of their bodies from carbon that comes from the air

The researchers from the Weizmann Institute predict that these bacteria may help in the future in reducing the accumulation of greenhouse gases in the atmosphere and in the fight against global warming

The bacteria in the laboratory of Prof. Ron Milo at the Weizmann Institute of Science succeeded where many fail - they were completely weaned from sugar, and they now feed only on carbon dioxide which they receive from their environment. In other words, these bacteria "live from the air" and build their entire biomass, their entire body, solely from carbon that comes from the atmosphere. It did not happen overnight: almost a decade of intelligent planning, genetic engineering and an accelerated version of "evolution in the laboratory" were required to reach these results, which are published today in the scientific journal Cell. This achievement holds many future possibilities for the development of new and green technologies that will help reduce the accumulation of greenhouse gases in the atmosphere and combat global warming.

Life on Earth is based, in one way or another, on "carbon fixation" through photosynthesis: the ability of certain plants, algae and bacteria to "suck" carbon dioxide from the environment and convert it - with the help of solar energy - into sugars that serve as a necessary starting material for processes Life. These organisms are at the bottom of the food web, and are called autotrophic organisms or producers. At the top of the food web, there are creatures that work in the opposite direction: they consume sugars (produced by producers) and "in return", release carbon dioxide into the environment. These creatures are called heterotrophs or consumers and they include many bacteria, fungi, animals, including humans. But is it possible to "reprogram" a creature that is at the top of the food web, consumes sugars and releases carbon dioxide, so that it uses carbon dioxide from the environment and produces the sugars it needs to build its body? This is exactly the challenge that Prof. Milo's research group in the Department of Plant and Environmental Sciences wanted to face.

The researchers, led by Dr. Shmuel Glazer, decided to try to apply the "sugar-free challenge" to E. coli bacteria. First, the researchers mapped the genes essential for the carbon fixation process and added some of them to the genome of the bacteria in their laboratory. In addition, to replace the role of solar energy in photosynthesis, they inserted a gene into the bacteria that allows them to obtain energy from an available substance known as formate.

Equipping the bacteria with these "means of production" was not enough to get them to change their diet and another trick was needed to get them to reconsider their ways. Together with Roi Ben-Nisan, Yanon Bar-On and other research students, Dr. Glaser used "evolution in the laboratory" processes in order to wean the bacteria gradually from sugar. At each stage of the process, bacteria in the culture received a decreasing amount of sugar, but one that was enough for them not to starve, and at the same time gained an abundance of carbon dioxide and formate. The descendants of the bacteria that were able to gradually wean themselves off their dependence on sugar (which gave them an evolutionary advantage over bacteria that stuck to sugar), received less and less sugar, until after about six months of adapting to the new nutritional regime, some of them underwent the complete nutritional transformation, living and multiplying in the environment where the food originated The only one is carbon dioxide.

To check if the bacteria did not in some way "nibble" other nutrients, some of the Coli Island bacteria that underwent evolutionary development were fed carbon dioxide that contained a heavy isotope - C13. The bacterial body parts were weighed, and the weight they gained was compared with the mass that was added from eating the heavy carbon version. The analysis showed that the carbon atoms in the bacteria's bodies were all produced directly from carbon dioxide only.

At this stage, the scientists sequenced the genomes of the bacteria that were weaned from sugar, in order to identify the mutations that led to changes in dietary habits. Surprisingly, they found relatively few genetic changes - some changes related to the synchronization of the carbon fixation process, some changes related to the regulation of gene expression levels, and some other changes whose role is still unclear. "We hope that further research will reveal exactly how these genes adapted their activity," says Dr. Glaser.

The researchers believe that the "healthy" habits of these bacteria may turn out to be especially healthy for the planet. For example, biotech companies that currently use cell cultures of yeast or bacteria to produce industrial chemicals, will be able to produce these substances in the cells using carbon dioxide, instead of using a large amount of corn syrup from which they currently feed. However, it is important to note that at this stage the bacteria get their energy from formate - a non-renewable energy source. In the future, the researchers plan to complete the evolutionary process and "teach" bacteria to get the energy they need for carbon fixation, from renewable energy sources. In such a scenario, the bacteria would produce a renewable carbon fuel that would be neutral in terms of carbon emissions into the atmosphere, since its carbon source would be the carbon dioxide in the air.

"Our laboratory was the first to deal with the idea of ​​changing the diet of the heterotroph - an organism that feeds on organic substances - and converting it to an autotroph - an organism that 'lives from the air'," says Prof. Milo. "It sounded impossible at first, but we learned a lot along the way, and in the end, we showed it was doable. Our findings constitute a significant milestone on the way to our goal - efficient and green scientific applications."