Integrating Applied Current and Microbial Metabolism

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Drew MacKellar, Sarah Glaven, Jeff Way, Pam Silver

Harvard Medical School, United States

Electrical current is ubiquitous in human civilization, where it serves as a versatile energy source and medium of information transmission. Electricity would also make an inexpensive input for biotechnology applications, where it could be used to drive microbial metabolism to produce commodities like fuels. This will require a robust interface between solid-state electronics and the aqueous chemistry of living cells. In most bacteria, the machinery for interconverting chemical and electrical energy – the electron transport chain – is separated from the environment by a nonconductive outer membrane. The best-studied conduit across this space at present is the metal reducing (Mtr) cytochromes of the gammaproteobacterium Shewanella. These bacteria use their periplasmic and outer membrane cytochromes to respire anaerobically onto solid iron and manganese, and recent studies indicate that they can also carry current in reverse, delivering electrons from an electrode to the inner membrane, where they could potentially be used to power synthetic pathways. We are studying the electrophysiology and gene expression dynamics of current delivered through the Mtr cytochromes, both in their native context in Shewanella, and in Escherichia coli cells engineered to express these genes. The lessons learned in these studies will be applied to the improvement of the electrode:bacterium interface, which may reduce costs and increase control over commodity production from microbes.