Extracellular Electron Transfer Enables Methanol Fermentation in Acetogen Eubacterium limosum

Area of Science:

• Microbial biotechnology
• Biochemical engineering
• Circular carbon economy

Background:

• Global warming necessitates a circular carbon economy.
• Methanol is a key energy carrier and biotechnological substrate.
• Eubacterium limosum converts methanol to chemicals but requires cosubstrates.

Purpose of the Study:

• To enable methanol fermentation without carbon cosubstrates using Eubacterium limosum.
• To investigate the role of extracellular electron transfer (EET) in this process.
• To identify key mediators in EET-driven methanol conversion.

Main Methods:

• Fermentation of methanol using Eubacterium limosum with ferrihydrite as an electron acceptor.
• Physiological analysis to identify essential components for EET.
• Proteomic analysis to elucidate metabolic pathways.

Main Results:

• Ferrihydrite-assisted methanol fermentation produced valuable chemicals, including hexanoate, without carbon cosubstrates.
• Cysteine (Cys-SH) was identified as essential for indirect extracellular electron transfer (EET).
• Eubacterium limosum demonstrated cysteine/cystine recycling, enabling thiol regeneration for EET.

Conclusions:

• A novel EET-driven process enables direct methanol fermentation by Eubacterium limosum.
• Cysteine-mediated electron transfer is crucial for this sustainable biotechnology.
• This research advances understanding of microbial carbon cycling and bio-production.