The need for sustainable alternatives to fossil fuels pushes scientists to look at the metabolic potential of microbes. Some can use carbohydrates, based on complex organic biomass or glucose, or even inorganic carbon to produce biofuels as a green alternative. The study “Electron conductive compounds alter fermentative pathways and cooperation in Clostridium carboxidivorans and Clostridium acetobutylicum in co-culture” in FEMS Microbiology Ecology explores a bacterial co-culture to optimise bioalcohol production, as explained by Lluis Bañeras on this #FEMSmicroBlog. #FascinatingMicrobes
Tiny partners, great outcomes (when working together)
Microbial production of biofuels has been known and optimised for a long time. However, microbes are rarely ever found as pure cultures in nature as they generally form complex communities. Within those, they share nutrients and energy, and establish complex relationships using yet-to-be discovered languages.
Microbial co-culture fermentation comes with significant advantages over single culture fermentation, since forcing microbial cooperation eventually opens up new possibilities.
The study “Electron conductive compounds alter fermentative pathways and cooperation in Clostridium carboxidivorans and Clostridium acetobutylicum in co-culture” in FEMS Microbiology Ecology aimed to create a microbial consortium using diverse carbon sources to produce various alcohols.
The role of electron-active compounds
For this, the study investigated Clostridium acetobutylicum, which specializes in producing acetone, butanol and ethanol, and Clostridium carboxidivorans, which uses C1 gases as substrates to produce hexanol, butanol and ethanol.
Sugar fermentation for alcohol production releases high amounts of CO2 as a by-product. Hence, the idea behind this pairing was to increase carbon recycling as well as product yields.
For any microbial consortium to work efficiently, electron availability plays a key role. Bacteria use and produce electrons in key metabolic reactions as reducing equivalents. That’s why adding conductive materials aimed at exchanging electrons promotes microbial interactions and balances their metabolisms.
The study tested different abiotic electron-conductive materials: activated carbon, magnetite, or iron oxides. These electron-active compounds were added to Clostridium acetobutylicum and Clostridium carboxidivorans cultures with the goal of supporting them to convert sugars into alcohols.
Magnetite increases collaborative alcohol production and carbon recovery
The most effective compound in terms of alcohol production and carbon recovery was magnetite, an iron-conductive compound with the formula Fe3O4. Why do magnets exert this beneficial effect in a microbial consortium?
The study hypothesised that the bacteria use magnetite as both a sink and source for electrons. It stores excess electrons produced during sugar fermentation and slowly releases them for alcohol production and CO2 fixation.
Data showed that Clostridium carboxidivorans used magnetite to mostly get rid of reducing equivalents produced during glycolysis. Supplementing Clostridium carboxidivorans pure cultures with magnetite decreased ethanol production by half.
This effect was reversed in the presence of the second partner, Clostridium acetobutylicum, as butanol and hexanol production increased 3-fold; a win-win interaction.
Iron oxides, the key components of magnetite, likely play a role in the interaction. In fact, adding soluble iron was also beneficial for alcohol production in the co-culture, although to a lesser extent compared to magnetite.
The results suggest that iron availability, in addition to magnetite’s conductive capacity, may be the primary factor for the increased alcohol fermentation in the co-culture. Altogether, these results provide valuable insights into the role of conductive materials in promoting redox reactions and electron transfer between bacteria when aiming to improve alcohol production using synthetic communities.
- Read the article “Electron conductive compounds alter fermentative pathways and cooperation in Clostridium carboxidivorans and Clostridium acetobutylicum in co-culture” by Feliu-Paradeda et al. in FEMS Microbiology Ecology (2025).
Sebastià Puig: Associate professor Serra Húnter at the University of Girona (Spain). He is interested in giving contaminated water and recalcitrant carbon dioxide (CO2) streams a second chance.
Lluís Bañeras: Associate professor of microbiology and researcher at the Institute of Aquatic Ecology. Anaerobic microbiology and physiology are his most beloved research topics.
Laura Feliu-Paradeda: Recently finished her PhD thesis, focused on Clostridium co-culture and on developing molecular tools to better understand them during co-culture fermentations.
About this blog section
The section #FascinatingMicrobes for the #FEMSmicroBlog explains the science behind a paper and highlights the significance and broader context of a recent finding. One of the main goals is to share the fascinating spectrum of microbes across all fields of microbiology.
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