Engineering a bi-directional cellular-electrical adapter in E. coli

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Matthew Hepler, Heather Jensen, Cheryl Goldbeck, Yancey Appling, Nicole Beedle, Caroline Ajo-Franklin

Lawrence Berkeley National Lab, United States

Cellular-electrical connections have the potential to combine the distinct capabilities of electronic technologies and living systems. Our research seeks to optimize bi-directional flow of electrons between cells and an electrode, to enable new possibilities in bioenergy, biosensing and bioremediation. We have pioneered a novel genetic approach, in which the electron transfer (ET) pathway from Shewanella oneidensis1 is transplanted into a heterologous organism, providing a molecularly defined route for intracellular electron to move to extracellular electron acceptors.2 The efficacy of this pathway to carry out inward electron transfer has been demonstrated in S. oneidensis, where the reduction of Fumarate to Succinate was carried out using a cathode as the sole electron donor.3 Current work in our group focuses on utilizing the recombinant ET pathway to carry out bio-electrosynthesis in E. coli. In S. oneidensis, the components of the ET pathway are able to directly transfer electrons to the Fumarate reductase, and the electrons are not transferred into the cytoplasm where they would be needed for other electro-synthetic reactions. In E. coli however, the components of the recombinant ET pathway are separated from the Fumarate reductase by the inner membrane; the successful reduction of Fumarate requires electron transfer through the menaquinone pool to a reduction center located in the cytoplasm. Successful inward electron transfer will demonstrate the synthesis of a biological bi-directional cellular-electrode electrical adapter, providing a route for reducing equivalents to move between the extracellular space, and cytoplasm. Future work will focus on studying the effect of intercellular electron transfer on driving the flux of fermentative pathways, potentially leading to an increased capacity of E. coli to synthesize certain economically important products in higher yield and purity.