Engineering of a synthetic electron conduit in living cells.

Department of Chemistry and Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 10/2010; 107(45):19213-8. DOI: 10.1073/pnas.1009645107
Source: PubMed

ABSTRACT Engineering efficient, directional electronic communication between living and nonliving systems has the potential to combine the unique characteristics of both materials for advanced biotechnological applications. However, the cell membrane is designed by nature to be an insulator, restricting the flow of charged species; therefore, introducing a biocompatible pathway for transferring electrons across the membrane without disrupting the cell is a significant challenge. Here we describe a genetic strategy to move intracellular electrons to an inorganic extracellular acceptor along a molecularly defined route. To do so, we reconstitute a portion of the extracellular electron transfer chain of Shewanella oneidensis MR-1 into the model microbe Escherichia coli. This engineered E. coli can reduce metal ions and solid metal oxides ∼8× and ∼4× faster than its parental strain. We also find that metal oxide reduction is more efficient when the extracellular electron acceptor has nanoscale dimensions. This work demonstrates that a genetic cassette can create a conduit for electronic communication from living cells to inorganic materials, and it highlights the importance of matching the size scale of the protein donors to inorganic acceptors.

1 Bookmark
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Background Microbial electrosynthesis and electro fermentation are techniques that aim to optimize microbial production of chemicals and fuels by regulating the cellular redox balance via interaction with electrodes. While the concept is known for decades major knowledge gaps remain, which make it hard to evaluate its biotechnological potential. Here we present an in silico approach to identify beneficial production processes for electro fermentation by elementary mode analysis. Since the fundamentals of electron transport between electrodes and microbes have not been fully uncovered yet, we propose different options and discuss their impact on biomass and product yields.ResultsFor the first time 20 different valuable products were screened for their potential to show increased yields during anaerobic electrically enhanced fermentation. Surprisingly we found that an increase in product formation by electrical enhancement is not necessarily dependent on the degree of reduction of the product but rather the metabolic pathway it is derived from. We present a variety of beneficial processes with product yield increases of maximal 36% in reductive and 84% in oxidative fermentations and final theoretical product yields up to 100%. This includes compounds that are already produced at industrial scale such as succinic acid, lysine and diaminopentane as well as potential novel bio-commodities such as isoprene, para-hydroxybenzoic acid and para-aminobenzoic acid. Furthermore, it is shown that the way of electron transport has major impact on achievable biomass and product yields. The coupling of electron transport to energy conservation could be identified as crucial for most processes.Conclusions This study introduces a powerful tool to determine beneficial substrate and product combinations for electro-fermentation. It also highlights that the maximal yield achievable by bio electrochemical techniques depends strongly on the actual electron transport mechanisms. Therefore it is of great importance to reveal the involved fundamental processes to be able to optimize and advance electro fermentations beyond the level of lab-scale studies.
    BMC Bioinformatics 12/2014; 15(1):6590. DOI:10.1186/s12859-014-0410-2 · 2.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The synthesis of metal nanoparticles by using bacteria is of growing interest in nanobiotechnology as well as in the study of microbial metal metabolism. Some silver-resistant bacteria can produce considerable amounts of silver particles when exposed to silver salts at high concentration but the mechanism of biosynthesis is unknown. In this work, an Escherichia coli strain that carries chromosomally encoded silver resistance determinants has been shown to produce silver nanoparticles in the periplasmic space when it was exposed to Ag(I) salts, providing a prototypical model for studying the biosynthesis of silver nanoparticles. The synthesized silver nanoparticles are in the form of a zero-valent metallic silver lattice, and the production of which was observed to be favorable under anaerobic conditions, suggestive of the biological reduction of Ag+ ions. As the microbial c-type cytochromes are known to mediate respiratory reduction of metal ions, their role in the biosynthesis of silver nanoparticles was examined. A deletion mutant of the cytoplasmic membrane-anchored tetra-heme c-type cytochrome subunit of periplasmic nitrate reductase (NapC) showed markedly reduced production of silver nanoparticles. On the other hand, re-introduction of the NapC could recover the biosynthesis of the silver nanoparticles. This study has identified a molecular mechanism of biosynthesis of silver nanoparticles involving c-type cytochromes, having implications in the bioenvironmental process of mineralization and the synthetic biology of metal nano-materials.
    Chemical Science 01/2014; 5(8):3144. DOI:10.1039/c4sc00138a · 8.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Multi-haem cytochromes are employed by a range of microorganisms to transport electrons over distances of up to tens of nanometres. Perhaps the most spectacular utilization of these proteins is in the reduction of extracellular solid substrates, including electrodes and insoluble mineral oxides of Fe(III) and Mn(III/IV), by species of Shewanella and Geobacter. However, multi-haem cytochromes are found in numerous and phylogenetically diverse prokaryotes where they participate in electron transfer and redox catalysis that contributes to biogeochemical cycling of N, S and Fe on the global scale. These properties of multi-haem cytochromes have attracted much interest and contributed to advances in bioenergy applications and bioremediation of contaminated soils. Looking forward, there are opportunities to engage multi-haem cytochromes for biological photovoltaic cells, microbial electrosynthesis and developing bespoke molecular devices. As a consequence, it is timely to review our present understanding of these proteins and we do this here with a focus on the multitude of functionally diverse multi-haem cytochromes in Shewanella oneidensis MR-1. We draw on findings from experimental and computational approaches which ideally complement each other in the study of these systems: computational methods can interpret experimentally determined properties in terms of molecular structure to cast light on the relation between structure and function. We show how this synergy has contributed to our understanding of multi-haem cytochromes and can be expected to continue to do so for greater insight into natural processes and their informed exploitation in biotechnologies. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
    Journal of The Royal Society Interface 01/2015; 12(102):20141117. DOI:10.1098/rsif.2014.1117 · 3.86 Impact Factor


Available from
May 28, 2014