Bacteria as climate heroes

Circular economy for CO₂

"The economy of the future must be carbon neutral," demands Stefan Pflügl. However, since carbon is an important component of many products -- such as fuel or plastics -- the existing CO₂should be recycled and returned to the cycle. One climate-neutral way to do this is capture CO₂directly from the air and convert it into formate with the help of renewable energy. This compound of carbon, oxygen and hydrogen can ultimately be a basic building block of the bioeconomy. The advantages of formate are that it is easy to transport and can be used flexibly for the production of chemicals and fuels. These substances can be produced with the help of acetogenic bacteria that feed on carbon compounds and produce acetic acid from them.

Formate recycling byA. woodii

In order to use acetogens for the production of raw materials, one needs to understand their metabolism and physiology. AlthoughA. woodiiis a model organism, meaning that the bacterium has already been extensively studied, the research team wanted to make a comparative observation. Thus, Stefan Pflügl and his team investigated how substrates such as formate, hydrogen, carbon monoxide, carbon dioxide or fructose affect the metabolism ofA. woodii.

"The biggest difference, caused by the different substrates, is the amount of energy thatA. woodiigains," observes Stefan Pflügl. He explains this as follows: "Acetogens are true survival artists that can also metabolise substrates such as CO, CO₂or formate. This is due to the fact that acetogens use what is probably the oldest metabolic pathway for CO₂fixation. Thus, they also manage to produce enough energy to survive under extreme conditions and from alternative food sources."

This means that acetogens are not only able to utilise CO₂but also do so very efficiently. Consequently, only little energy needs to be expended to convert CO₂into formate, which is then converted into the basic chemical acetic acid.

Replacement of oil-based products

To exploit the full potential ofA. woodii, the researchers also investigated how the bacterium can be genetically modified to produce ethanol or lactic acid instead of acetic acid. While ethanol forms the basis for fuel, lactic acid can be used to produce biodegradable plastics. Oil-based substances could consequently be replaced by more sustainable alternatives. "Not only would this be in the sense of the bioeconomy, but CO₂and carbon monoxide, which are produced during the combustion of fuel or plastic, could also be recycled to the original product," Stefan Pflügl envisages.

The study, which has been published in the journalMetabolic Engineering, thus provides insights into whatacetogenslikeA. woodiican do under certain conditions. Based on the experimental data and using a model, the researchers also developed strategies on howA. woodiican be genetically manipulated and used for the production of other substances.