Direct electron uptake from a cathode using the inward Mtr pathway in Escherichia coli

Area of Science:

• Bioelectrochemistry
• Microbial metabolism
• Synthetic biology

Background:

• Bioelectrochemical systems (BES) utilize microbial catalysts for electricity-driven chemical production.
• Extracellular electron transfer (EET) is crucial in BES, but inward EET mechanisms from cathodes to microbes are poorly understood.
• Limited EET capability hinders practical applications of BES for chemical synthesis.

Purpose of the Study:

• To engineer Escherichia coli with an inward Mtr pathway for enhanced extracellular electron transfer (EET).
• To investigate the mechanism of inward EET and its role in microbial energy metabolism.
• To improve electricity-driven production of chemicals using engineered microbes in BES.

Main Methods:

• Engineered *Escherichia coli* by expressing the *ccmABCDEFGH* (from *E. coli*) and *mtrABC* (from *Shewanella oneidensis*) genes to introduce the Mtr pathway.
• Applied electrochemical pressure for selection and evolution of engineered *E. coli*.
• Analyzed succinate production, electroactivity, menaquinone's role in inward EET, and intracellular NADH/ATP levels.

Main Results:

• Evolved *E. coli* demonstrated increased succinate production in direct BES.
• Engineered *E. coli* exhibited enhanced electroactivity.
• Menaquinone was identified as a key component of inward EET, essential for fumarate reduction; distinct energy conservation coupling was observed compared to electron mediators.

Conclusions:

• The Mtr pathway engineering enables enhanced inward EET in *E. coli* for BES applications.
• Menaquinone plays a critical role in the inward EET mechanism and fumarate reduction.
• Engineered *E. coli* offers a promising platform for efficient electricity-driven chemical production.