Syngas Fermentation and Metabolic Engineering Dynamics

Syngas fermentation harnesses the capacity of anaerobic microorganisms to convert synthesis gas—a mixture of carbon monoxide, carbon dioxide and hydrogen—into fuels and chemicals via specialised biochemical pathways. Central to this process is the Wood–Ljungdahl pathway, by which acetogenic bacteria fix CO and CO₂ into acetyl‐coenzyme A, coupling carbon assimilation with energy conservation through ion gradients. Electron‐bifurcation mechanisms further optimise redox balancing by simultaneously driving endergonic and exergonic reactions, enhancing the metabolic flexibility of key enzymes. Metabolic engineering has refined these natural capabilities by rewiring gene networks, introducing heterologous pathways and modulating electron transfer complexes to steer product profiles towards ethanol, higher alcohols, organic acids or longer‐chain chemicals. Advances in systems biology and synthetic biology have elucidated regulatory circuits, enzyme structures and membrane transport systems, enabling dynamic control of gas uptake, cofactor regeneration and pathway flux. Together, these developments underscore the global significance of syngas bioconversion as a platform for sustainable low-carbon fuels and high-value biochemicals, while addressing challenges of reactor design, mass transfer, thermodynamic limits and scale-up.

Research from Nature Portfolio

Recent structural studies have unveiled the molecular architecture of a novel electron‐bifurcating transhydrogenase complex from an acetogenic species. High-resolution cryo-EM reveals how modular subunits assemble to channel electrons between ferredoxin, NADH and NADP+, clarifying strategies for redox coupling at thermodynamic extremes. These insights inform the design of engineered electron-transfer enzymes with tailored bifurcation activities, offering routes to boost cofactor recycling in syngas-fed bioprocesses. Separately, work on anaerobic non-photosynthetic mixotrophy demonstrates that co-utilisation of organic substrates and CO₂ in a single acetogen can surpass theoretical yield limits. By supplying additional reductant (for example hydrogen) and redirecting carbon flux through engineered acetone production, this approach achieves net yields beyond conventional fermentation, while minimising CO₂ emissions.

Syngas Fermentation and Metabolic Engineering Dynamics publication trend

The graph below shows the total number of articles in syngas fermentation and metabolic engineering dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Syngas: A mixture of CO, CO₂ and H₂ derived from gasification of carbonaceous feedstocks.

Wood–Ljungdahl pathway: The biochemical route by which acetogens fix CO₂/CO into acetyl-CoA, coupling carbon fixation to energy conservation.

Electron bifurcation: A mechanism in which a single flavoprotein or enzyme complex couples an exergonic electron transfer to an endergonic one, optimising redox balance.

Chain elongation: A microbial process that extends carboxylate chains by reverse β-oxidation, producing medium-chain fatty acids and alcohols.

Metabolic engineering: The directed modification of cellular pathways to enhance production of target compounds through genetic and regulatory interventions.

References

1. Gas Fermentation—A Flexible Platform for Commercial Scale Production of Low-Carbon-Fuels and Chemicals from Waste and Renewable Feedstocks. Frontiers in Microbiology (2016).
2. An Ancient Pathway Combining Carbon Dioxide Fixation with the Generation and Utilization of a Sodium Ion Gradient for ATP Synthesis. PLOS ONE (2012).
3. Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review. Frontiers in Microbiology (2018).
4. Molecular architecture and electron transfer pathway of the Stn family transhydrogenase. Nature Communications (2023).
5. CO2 fixation by anaerobic non-photosynthetic mixotrophy for improved carbon conversion. Nature Communications (2016).
6. Moorella thermoacetica: A promising cytochrome- and quinone-containing acetogenic bacterium as platform for a CO2-based bioeconomy. Green Carbon (2023).
7. Production of medium-chain fatty acids and higher alcohols by a synthetic co-culture grown on carbon monoxide or syngas. Biotechnology for Biofuels and Bioproducts (2016).
8. Metabolic engineering of Clostridium autoethanogenum for selective alcohol production. Metabolic Engineering (2017).