Bioelectrochemical systems and synthetic biology: more power, more products

Abstract

Microbial electrochemical technologies (METs) are applications or processes that utilize the electrochemical interaction of microbes and electrodes (Schroder et al., 2015). It has been known for over 100 years (Potter, 1911) that microorganisms can form electrical connections to devices, but only recently (approximately 20 years) has this concept been put to technological use. Microbial electrochemistry and electromicrobiology have grown as disciplines due to an intense interest in the possibility of using MET for alternative energy, wastewater treatment and biofuels production. METs have the potential to contribute to a circular economy, where carbon is cycled back into products or electricity from renewable sources. For these reasons, MET represent a significant and attractive source of new enterprise and employment creation. The natural physiological activity of electroactive bacteria, those capable of extracellular electron transfer (EET), has been studied intensely over the past two decades in order to improve efficiency and productivity of METs. A diverse group of scientists has contributed to this knowledge base including microbiologists, electrochemists, physicists, biochemists and molecular biologists. Genetic engineering has been used to determine the molecular underpinnings responsible for carrying charge between cells and the electrode of the two model EET organisms, Geobacter sulfurreducens and Shewanella oneidensis. New electroactive organisms have been discovered using genomics (Eddie et al., 2016), and new ways to transform electrode-associated microbial communities are being developed. Electrochemistry, advanced imaging techniques and modelling have all been employed to track the movement of electrons through biofilms and purified proteins. New lexicons have been created to allow interdisciplinary discussions of extracellular electron transfer, and an entire Center for Electromicrobiology has been funded at Aarhus University in Denmark. Our growing knowledge of the principles of EET is now poised to intersect with the nascent field of synthetic biology to bring about the next generation of MET for power and energy, microbial electrosynthesis and microbial bioelectronics. Synthetic biology is an emerging field that has grown out of the principles of biology and engineering disciplines, devoted to the rational design and engineering of organisms and their components (Church et al., 2014). It is now possible to both engineer specific functions into living systems and construct entirely new ones (Liu et al., 2018a,2018b). Microorganisms are viewed as tiny supercomputers that can be programmed as such by reading, writing and editing the cell’s DNA. Genetic circuits can be designed computationally to wire cells for on-demand functionality (Nielsen et al., 2016), and these circuits can be printed and shipped to a scientist at the bench to deploy in the organism of their choice (Libby and Silver, 2019). Growth of the field of synthetic biology has resulted in the development of new tools and approaches in molecular genetics to advance biotechnology across a wide application space. For example, it is now possible to precisely tune gene expression from 12 independent small-molecule sensors engineered into the genome of E. coli (Meyer et al., 2018) or confer the ability of a bacterial cell to ‘see’ different wavelengths of light and respond in a pre-programmed manner (Fernandez-Rodriguez et al., 2017). Synthetic biology has the potential to advance microbial electrochemical technologies (MET) by bringing new design platforms to engineer EET pathways in organisms that do not naturally have them, modify microbial metabolism to improve EET rates and increase the diversity of products from microbial electrosynthesis. Two examples are given below: (i) enhanced power output from microbial fuel cells and (ii) the potential for microbial electrosynthesis to be a viable approach for fuels or molecules production.

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Identifiers

DOI

10.1111/1751-7915.13456

Journal

Microbial Biotechnology

Year

2019