Chemistry

The Emergence of Microbial Electrochemistry In Biotechnology
Daniel R. Bond, BioTechnology Institute and Department of Microbiology University of Minnesota - Twin Cities dbond@umn.edu

Over thirty years ago, the discovery that some proteins could directly transfer electrons to electrodes created the field of protein electrochemistry. While only a few proteins naturally had redox centers accessible to electrodes, a combination of protein engineering and conductive materials expanded the range of useful enzymes, and formed the basis for a new generation of biosensors and bioelectrical devices. A similar discovery occurred more recently, where specialized bacteria were shown to generate electrical current by transferring electrons from their membranes to electrodes in rudimentary fuel cells. While batteries and devices powered by microbial metabolism had been proposed for nearly a century, the demonstration that some bacteria naturally had electrical conduits spanning their membranes for respiration to external acceptors made a plethora of new bioelectrical applications possible. Over the past decade, the field that began with simple electricity-producing Microbial Fuel Cells diverged to encompass hydrogen- methane- and caustic-producing Microbial Electrolysis Cells, salt-concentrating Microbial Desalination Cells, as well as bioelectrochemical reactors treating nitrogen-, phosphorous- and sulfur-rich wastes. Advances in genetic techniques, genome sequencing, and biochemical analysis of large multiheme cytochromes and other conductive structures on these cells has revealed a great deal of complexity in the mechanisms that power these electron transfer reactions, leading to the first organisms engineered to produce electricity or use electrodes in a portion of their metabolism. Powering microbial carbon fixation pathways to capture carbon and produce fuels, known as bioelectrosynthesis, emerged as another long-range target for engineering.

During this short period of research, surprising microbial electron transfer strategies have been discovered, that link bacteria to each other via direct connections, which could also be adapted to deliver electrons to our electrical world. In addition, there are many unexplored environments in which bioelectrochemical systems could harness bacteria to recover both nutrients and energy.

Background Review Article:

Logan, Bruce E., and Korneel Rabaey. "Conversion of wastes into bioelectricity and chemicals by using microbial electrochemical technologies." Science 337.6095 (2012): 686-690.

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Chemistry

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