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Extracellular electron transfer (EET) is a process that microorganisms use to reduce or oxidize external insoluble electron acceptors or donors. Much of our mechanistic understanding of this process is derived from studies of transmembrane cytochrome complexes and extracellular redox shuttles that mediate outward EET to anodes and external electron acceptors. In contrast, there are knowledge gaps concerning the reverse process of inward EET from external electron donors to cells. Here, we describe a role for soluble iron (exogenous FeCl2) in enhancing EET from cathodes to the model EET bacterium Shewanella oneidensis MR‐1, with fumarate serving as the intracellular electron acceptor. This iron concentration‐dependent electron uptake was eradicated upon addition of an iron chelator and occurred only in the presence of fumarate reductase, confirming an electron pathway from cathodes to this periplasmic enzyme. Moreover, S. oneidensis mutants lacking specific outer membrane and periplasmic cytochromes exhibited significantly decreased current levels relative to wild‐type. These results indicate that soluble iron can function as an electron carrier to the EET machinery of S. oneidensis. [ABSTRACT FROM AUTHOR]

Desulfarculus baarsii and Desulfurivibrio alkaliphilus are strictly anaerobic bacteria existing in marine sediments. D. baarsii gains energy through reducing sulphate and D. alkaliphilus is able to reduce elemental sulphur, thiosulphate and polysulphide in seawater. Both organisms were previously identified as key organisms in sediment derived, bidirectional electroactive biofilms. Here, we investigated the electrochemical performance of these two bacteria in bio‐electrochemical systems and their possible involvement in anodic and cathodic reactions. The results show that D. baarsii was unable to donate or accept electrons to/from an electrode, while D. alkaliphilus was able to catalyse both anodic and cathodic reactions and interact with the electrode through direct or potentially indirect electron transfer. Raman spectra of D. alkaliphilus electrode biofilms showed a high similarity to Geobacter sulfurreducens biofilms, including the specific bands of cytochromes b and c, explaining the electroactivity of D. alkaliphilus in bioelectrochemical reactions. [ABSTRACT FROM AUTHOR]

Cyanobacteria form dense blooms that impair water quality. Although the impact of blooms on water quality largely differs depending on the species of cyanobacteria, it is challenging to distinguish cyanobacterial species with conventional sensors due to their similar physicochemical properties. Here, we conducted cyclic voltammetry to three major bloom‐forming cyanobacteria, Synechococcus sp. Microcystis aeruginosa, and Anabaena circinalis without addition of redox active compounds nor chemical modifications of the working electrode. These cyanobacteria exhibited redox peaks with distinct potentials from each other, in the range of +0.60 – +0.75 V vs SHE. Because these redox potentials hardly overlap with those of other environmental electroactive bacteria, those redox peaks may be used as indicators of the onset of a cyanobacterial bloom. Given that the photo‐responsive current correlated with the cell density of Synechococcus sp. electrochemical measurement would be a promising technique for a novel cyanobacterial quantification sensor, with in‐built ability to identify cyanobacterial species. [ABSTRACT FROM AUTHOR]

In this study, the performance of electroactive bacteria (EAB), cultivated inside tubular electrode ducts, is systematically investigated to derive predictions on the behavior of EAB under conditions limited by electrochemical losses. A modeling approach is applied to assess the influence of the electrochemical losses on the electrochemical performance and scaling characteristics of complex 3D structures, such as sponges and foams. A modular flow reactor is designed that provides laminar and reproducible flow conditions as a platform for the systematic electrochemical and bioelectrochemical characterization of 3D electrodes in bioelectrochemical systems (BES). The bioelectrochemical experiments are carried out in a set of reactors incorporating cylindrical electrodes exhibiting ducts of 1 cm length and different diameters ranging from 0.1 cm up to 1 cm. Single duct calculations are extrapolated to three dimensions through geometrical considerations; trends in 3D bioanode performance are demonstrated using the resulting simplified 3D structure. The combined experimental and modeling approach constitutes a framework for future studies on systematic electrode design. [ABSTRACT FROM AUTHOR]

Bacterial cell appendix formation supports cell‐cell interaction, cell adhesion and cell movement. Additionally, in bioelectrochemical systems (BES), cell appendages have been shown to participate in extracellular electron transfer. In this work, the cell appendix formation of Clostridium acetobutylicum in biofilms of a BES are imaged and compared with conventional biofilms. Under all observed conditions, the cells possess filamentous appendages with a higher number and density in the BES. Differences in the amount of extracellular polymeric substance in the biofilms of the electrodes lead to the conclusion that the cathode can be used as electron donor and the anode as electron acceptor by C. acetobutylicum. When using conductive atomic force microscopy, a current response of about 15 nA is found for the cell appendages from the BES. This is the first report of conductivity for clostridial cell appendices and represents the basis for further studies on their role for biofilm formation and electron transfer. [ABSTRACT FROM AUTHOR]

We have explored a new concept in bacteria-electrode interaction based on the use of fluid-like electrodes and planktonic living cells. We show for the first time that living in a biofilm is not a strict requirement for Geobacter sulfurreducens to exchange electrons with an electrode. The growth of planktonic electroactive G. sulfurreducens could be supported by a fluid-like anode as soluble electron acceptors and with electron transfer rates similar to those reported for electroactive biofilms. This growth was maintained by uncoupling the charge (catabolism) and discharge (extracellular respiration) processes of the cells. Our results reveal a novel method to culture electroactive bacteria in which every single cell in the medium could be instantaneously wired to a fluid-like electrode. Direct extracellular electron transfer is occurring but with a new paradigm behind the bacteria-electrode interaction. [ABSTRACT FROM AUTHOR]

Keywords: electron uptake; electrosynthesis; extracellular electron transfer; microbial electrochemistry; Shewanella EN electron uptake electrosynthesis extracellular electron transfer microbial electrochemistry Shewanella 1 1 1 02/17/23 20230213 NES 230213 B The Cover Feature b illustrates soluble iron acting as an electron mediator for enhanced extracellular electron uptake by I Shewanella oneidensis i MR-1. Cover Feature: Soluble Iron Enhances Extracellular Electron Uptake by Shewanella oneidensis MR-1 (ChemElectroChem 4/2023) Electron uptake, electrosynthesis, extracellular electron transfer, microbial electrochemistry, Shewanella. [Extracted from the article]

ABSTRACT Extracellular electron transfer pathways allow certain bacteria to transfer energy between intracellular chemical energy stores and extracellular solids through redox reactions. Microorganisms containing these pathways, exoelectrogens, are a critical part of microbial electrochemical technologies that aim to impact applications in bioenergy, biosensing, and biocomputing. However, there are not yet any examples of economically viable microbial electrochemical technologies due to the limitations of naturally occurring exoelectrogens. Here we first briefly summarize recent discoveries in understanding extracellular electron transfer pathways, then review in-depth the creation of customized and novel exoelectrogens for biotechnological applications. We analyze engineering efforts to increase current production in native exoelectrogens, which reveals that modulating certain processes within extracellular electron transfer are more effective than others. We also review efforts to create new exoelectrogens and highlight common challenges in this work. Lastly, we summarize work utilizing engineered exoelectrogens for biotechnological applications and the key obstacles to their future development. Fueled by the development of genetic tools, these approaches will continue to expand and genetically modified organisms will continue to improve the outlook for microbial electrochemical technologies. Biotechnol. Bioeng. 2016;113: 687-697. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Cover Feature: Synechococcus and Other Bloom-Forming Cyanobacteria Exhibit Unique Redox Signatures (ChemElectroChem 2/2021) Keywords: cyanobacterial sensor; extracellular electron transfer; microbial electrochemistry; electrochemical detection; electrochemical sensor EN cyanobacterial sensor extracellular electron transfer microbial electrochemistry electrochemical detection electrochemical sensor 271 271 1 02/01/21 20210118 NES 210118 B The Cover Feature b shows that different species of cyanobacteria are blooming in a water body exposed to light, and a cyclic voltammogram provides an electrochemical signature for the presence of the cyanobacteria. Cyanobacterial sensor, extracellular electron transfer, microbial electrochemistry, electrochemical detection, electrochemical sensor. [Extracted from the article]

The Cover picture shows the bacteria‐electrode interaction between a fluid‐like electrode and planktonic living cells in a microbial electrochemical device. We show for the first time that a biofilm living mode is not a strict requirement for Geobacter sulfurreducens to perform extracellular electron transfer (EET) to an anode, an alternative to the paradigm of microbial EET in which electroactive bacteria colonize an electrically conductive surface to transfer electrons directly to it. More details can be found in the Full Paper by Tejedor‐Sanz et al. on page 693 in Issue 4, 2017 (DOI: 10.1002/cssc.201601329). [ABSTRACT FROM AUTHOR]