Publication date: 8th October 2020
Microorganisms precisely control biological processes, including biosynthesis and cell growth, by regulating the redox state of different biomolecules. These processes can be modulated by electrochemically coupling intracellular biomolecules to an external electrode, but current approaches afford only limited control and specificity. Here we describe using electrical current to reduce specific biomolecules, allowing control of biosynthesis and cell growth in two industrially relevant microorganisms, Escherichia coli and Lactobacillus plantarum.
To enable electrochemical control of E. coli, we used synthetic biology to introduce a heterologous electron transfer pathway. E. coli expressing mtrCAB from Shewanella oneidensis MR-1 consumed electrons directly from a cathode when fumarate or nitrate, both intracellular electron acceptors, were present. The fumarate-triggered current consumption occurred only when fumarate reductase was present, indicating all the electrons passed through this enzyme. Moreover, MtrCAB-expressing E. coli used current to stoichiometrically produce ammonia. Thus, our work introduces a modular genetic tool to reduce a specific intracellular redox molecule with an electrode, opening the possibility of electronically controlling biological processes such as biosynthesis and growth in any microorganism.
Complementing this approach, we discovered that L. plantarum, a lactic acid bacteria used industrially to produce fermented foods, can uptake electrons. This electron uptake occurs under anaerobic conditions when a terminal electron acceptor and its corresponding oxidioreductase are present. Unlike other anaerobic respiratory modes in L. plantarum, this current consumption does not require addition of co-factors such as heme or riboflavin. Electron uptake promotes cell growth and acidification of the media, both processes essential for food fermentation. We find that the L. plantarum metabolism is shifted towards ATP producing pathways in the presence of both a cathode and a suitable electron acceptor. This surprising discovery opens the possibility of using electrical current to drive industrial production of fermented foods using lactic acid bacteria.
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