UC Berkeley

Both organisms and human-made technological devices use the flow of charge as the basic currency of information and energy. The soft materials properties and waxy cell membranes generally do not interface electrically with solid materials. Creating an interface that permits electrical communication between living and non-living systems would enable new opportunities in fields such as biosensing, bioenergy conversion, and biocomputing. Thus my dissertation focuses on creating a blueprint for the bidirectional flow of electrons between living and non-living systems that is transferrable to a multitude of cell lines. I take a biologically-focused approach to connect the living and non-living worlds: use synthetic biology to introduce a new electron transfer pathway into E. coli. This strategy takes advantage of the respiratory capability of the dissimilatory metal reducing bacterium Shewanella oneidensis MR-1. Shewanella uses a network of multiheme cytochromes that are able to transfer charge across the inner and outer membranes of the bacteria via the heme moiety in the cytochromes. This pathway enables Shewanella to route electrons along a well-defined path from the cell interior to an extracellular inorganic material acting as a terminal electron acceptor during anaerobic respiration. By genetically engineering the cell to build and maintain the bioelectronic connections, the cells can autonomously assemble and repair these connections. This work describes the first time the outer membrane spanning and double membrane spanning Shewanella electron transfer pathway was heterologously expressed in Escherichia coli. Additionally, these engineered E. coli strains are shown to reduce soluble iron, solid iron oxide, and anodes. This work not only serves as a landmark for the expression of complex membrane associated pathways, but it also demonstrates proof of concept that this pathway could be transferrable to other cell lines. This dissertation represents the first step towards engineering bidirectional communications with electrodes, and it opens up an array of opportunities for studying the biochemical and enzymatic properties of these unique proteins as well as the potential for novel hybrid technologies.