Industrial microbe enables conversion of carbon monoxide to ethanol

Industrial microbe enables conversion of carbon monoxide to ethanol
by Robert Schreiber
Berlin, Germany (SPX) Oct 30, 2025

A team of scientists from the Max Planck Institute for Marine Microbiology, working with a colleague from the Max Planck Institute of Molecular Cell Biology and Genetics, has experimentally clarified the molecular mechanisms used by Clostridium autoethanogenum to transform industrial waste gases into ethanol. This microbe, originally isolated from rabbit droppings, thrives in environments containing pure carbon monoxide, which is fatal to most organisms. It consumes carbon monoxide to create cellular material and obtains energy through a specific sequence of chemical reactions.

C. autoethanogenum's capacity to tolerate and metabolize carbon monoxide has found wide application in industrial bioethanol production. Despite current industrial use, the pathway by which this bacterium converts carbon monoxide to ethanol was not fully understood. A critical disputed step in the process was the reduction of acetate to acetaldehyde. Some researchers questioned whether organisms could carry out this reduction. The present study, published in Nature Chemical Biology, experimentally confirms that C. autoethanogenum reduces acetate to acetaldehyde and resolves the scientific debate.

Central to the reaction is the enzyme aldehyde:ferredoxin oxidoreductase (AFOR), which contains a tungsten atom - the heaviest element found in biological systems - as well as iron-sulfur clusters that impart a dark brown color. The research team isolated AFOR and determined its atomic structure by X-ray crystallography, revealing the configuration of the tungsten-containing catalytic cofactor and surrounding elements. Initial preparations were inactive, but the team discovered a method to restore enzyme activity. According to co-author Melissa Belhamri, AFOR acts on various substrates and is capable of enabling the production of multiple alcohols in addition to ethanol.

To address how AFOR facilitates an energetically unfavorable reduction, researchers recreated the microbial process in vitro by combining AFOR with additional enzymes in a synthetic pathway. Their results demonstrated that it is possible to convert acetate into ethanol outside the cell, confirming the biological plausibility of the pathway.

This discovery provides essential insight into the metabolic strategy used by C. autoethanogenum and establishes a foundation for metabolic engineering. By uncovering the detailed function and reactivation of AFOR, and mapping the ethanol production pathway, the findings offer new avenues for enhancing the bioconversion of industrial waste gases into valuable fuels and chemicals. The process holds promise for broadening sources of microbial biofuel and advancing green technology applications in the circular carbon economy.

Research Report:Carbon monoxide-driven bioethanol production operates via a tungsten-dependent catalyst.