Fermentation

Edge evidence

• Fermentation uses organic substrate

  Fermentation uses an organic substrate as both electron donor and acceptor source.

  • DOI:10.3389/fmicb.2021.703525 substrate of a fermentation has to serve as electron donor as well as acceptor Supports organic substrate donor/acceptor role.
• organic substrate oxidation reduces reduced redox cofactors

  Substrate oxidation generates reduced redox cofactors.

  • DOI:10.1111/1751-7915.13746 a substrate is oxidized to an intermediate Review describes substrate oxidation with cofactor reduction in fermentation.
• reduced redox cofactors reoxidized by fermentation products

  Product-forming reductions regenerate oxidized cofactors.

  • DOI:10.1111/1751-7915.13746 after which the intermediate is reduced Supports product-side reduction and redox cofactor regeneration.
• Fermentation conserves energy by substrate-level phosphorylation

  Substrate-level phosphorylation is a major fermentative energy-conservation route.

  • DOI:10.1111/1751-7915.13746 main sources of energy under fermentative conditions Supports SLP as a fermentative energy mechanism.
• substrate-level phosphorylation produces ATP METPO:2000202

  Substrate-level phosphorylation directly forms ATP.

  • DOI:10.1111/1751-7915.13746 energy-rich bonds (for example via substrate-level phosphorylation) Supports SLP as ATP-linked energy conservation.
• Fermentation excludes external inorganic terminal electron acceptor

  Fermentation excludes use of external inorganic terminal electron acceptors, distinguishing it from anaerobic respiration.

  • DOI:10.1093/femsre/fuae016 Excludes processes that use external inorganic terminal acceptors, explicitly naming nitrate and sulfur respiration.
• glycolysis (Embden-Meyerhof-Parnas pathway) feeds into pyruvate

  Glycolysis (EMP) feeds carbon flux to pyruvate, the entry point for fermentation branches.

  • DOI:10.1093/femsre/fuae016 Glycolysis (EMP) and the pentose phosphate pathway feed to pyruvate.
• pyruvate:ferredoxin oxidoreductase produces reduced ferredoxin METPO:2000202

  Pyruvate:ferredoxin oxidoreductase oxidizes pyruvate and produces reduced ferredoxin.

  • DOI:10.1093/femsre/fuae016 Pyruvate:ferredoxin oxidoreductase produces reduced ferredoxin; central to redox balancing.
• ferredoxin:NAD+ oxidoreductase transfers electrons from reduced ferredoxin to NAD+

  Ferredoxin:NAD+ oxidoreductase reoxidizes reduced ferredoxin by transferring electrons to NAD+.

  • DOI:10.1093/femsre/fuae016 Ferredoxin-NAD+ reductase transfers electrons from reduced ferredoxin to NAD+; strong redox-balancing edge.
• flavin-based electron bifurcation reduces reduced ferredoxin METPO:2000017

  Flavin-based electron bifurcation couples exergonic and endergonic redox reactions, reducing low-potential ferredoxin.

  • DOI:10.1038/s41467-023-41212-x Couples an exergonic and an endergonic redox reaction within a single soluble enzyme complex, typically reducing low-potential ferredoxin.
• ion-motive force drives ATP synthase

  Ion-motive force generated during fermentation drives ATP synthase-mediated ATP formation.

  • DOI:10.1093/femsre/fuae016 Ion gradients drive ATP synthesis via ATP synthases; links fermentation to chemiosmotic ATP conservation.
• ATP synthase produces ATP METPO:2000202

  ATP synthase forms ATP using the ion-motive force.

  • DOI:10.1093/femsre/fuae016 ATP synthesis via ATP synthases driven by ion gradients during fermentation.