Unveiling Microbial Electrosynthesis: Scientists Uncover Expanded Chemical Production Capabilities of Bacteria

The Leibniz Institute for Natural Product Research and Infection Biology researchers have unraveled new insights into microbial electrosynthesis (MES), demonstrating that bacteria utilize electrons from hydrogen rather than directly from the supplied electric current.

Bacteria’s role in producing valuable chemicals using carbon dioxide and electricity

In microbial electrosynthesis, microorganisms convert CO2 and electricity into substances such as alcohol. Until recently, the specific biological mechanisms enabling this process were mostly theoretical. However, researchers at the Leibniz Institute have now confirmed experimentally that bacteria use electrons sourced from hydrogen, and can produce a more diverse range of chemical compounds than was previously believed.

Microbial electrosynthesis is seen as a promising way to combat climate change effects and aid the shift to renewable energy. It can bind carbon dioxide, create ethanol and other organic compounds that can serve as fuel, and consequently store excess electricity. Despite being known for over a decade, the technology has struggled to make significant progress toward commercialization.

Miriam Rosenbaum, the head of the Bio Pilot Plant at Leibniz-HKI, attributes this to the complex biology of the process, often seen as a “black box”. Rosenbaum, who is also the Chair of Synthetic Biotechnology at Friedrich Schiller University in Jena, has been devoted to understanding the intricacies of microbial electrosynthesis.

Her team has made a significant discovery in this area: they have shown that bacteria do not directly absorb the supplied electrons from the electric current. Instead, they use hydrogen as a medium for electron transfer. This theory had long been suggested but lacked experimental evidence. Furthermore, they discovered that the method can generate more useful chemicals than previously believed, and have optimized the process for maximum yields.

Controlled experimental environment

In MES, electricity is applied to an aqueous solution filled with microorganisms, along with the addition of carbon dioxide. These microorganisms employ electricity and carbon to produce organic compounds like ethanol or acetate, using the provided electrons. However, how they use these electrons had been unclear.

Rosenbaum states that a previous study theorized that microbes directly utilized the electrons, a hypothesis that remained unproven. She believed it was more plausible that microbes utilized hydrogen for their biosynthesis. This is because when electricity and carbon dioxide are applied, a process similar to classical electrolysis occurs, splitting water into hydrogen and oxygen.

Santiago Boto, the study’s lead author, explains that no one had directly measured hydrogen in the system until now. He adjusted the MES reactor to accurately control all parameters. He employed a pure culture of the bacterium Clostridium ljungdahlii in varying concentrations and monitored the electric current flow and the produced and released hydrogen using microsensors.

They gathered compelling evidence that the bacteria were indeed using hydrogen. When the bacteria concentration in the nutrient medium was enough to form a biofilm on the cathode, resulting in minimal measurable hydrogen in the electrode environment, bacterial activity drastically decreased. This also occurred when the voltage was insufficient for electrolysis. The bacteria only showed high activity when hydrogen was readily accessible from the electrode.

Unearthing new biosynthetic routes

The team optimized voltage and bacterial concentration for maximum acetate yields. “We achieved the highest acetate values to date for a pure culture of bacteria,” Boto noted. Additionally, he discovered that the bacteria produced amino compounds they do not typically create. Collaborating with Falk Harnisch from the Environmental Research Center in Leipzig, the team also discovered previously undescribed reactions between the nutrient medium and the cathode, which seemingly expedite the synthesis process.

The team aims to optimize the processes further and investigate the new findings more deeply. “Amino compounds are extremely interesting for the chemical industry, and the bacteria we used are already industrially deployed. We may have found a new production method for such chemicals,” Boto added. These findings should contribute to making MES commercially viable. “I anticipate a substantial rise in this technology in the coming years when we finally bring biology into focus,” Rosenbaum stated. The Bio Pilot Plant is working on this and collaborating with process engineers to design larger MES reactors.

The study titled, “Microbial electrosynthesis with Clostridium ljungdahlii benefits from hydrogen electron mediation and permits a greater variety of products” by Santiago T. Boto, Bettina Bardl, Falk Harnisch, and Miriam A. Rosenbaum, published on 17 May 2023 in Green Chemistry, was supported by the German Research Foundation under the eBiotech priority program.
DOI: 10.1039/D3GC00471F

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More about Microbial Electrosynthesis

• Leibniz Institute for Natural Product Research and Infection Biology
• Friedrich Schiller University in Jena
• Environmental Research Center in Leipzig
• German Research Foundation
• Green Chemistry Journal