Research Library

Zhiyong Zheng, Yong Xiao, Ranran Wu et al.

Biosensors and Bioelectronics · 2019

Han Bao, Zhanwang Zheng, Bin Yang et al.

Bioelectrochemistry · 2016

Weiqiang Lin, Zhou‐Hua Cheng, Qi-Zhong Wu et al.

ACS Synthetic Biology · 2024

Electroactive bacteria, exemplified by Shewanella oneidensis MR-1, have garnered significant attention due to their unique extracellular electron-transfer (EET) capabilities, which are crucial for energy recovery and pollutant conversion. However, the practical application of MR-1 is constrained by its EET efficiency, a key limiting factor, due to the complexity of research methodologies and the challenges associated with the practical use of gene editing tools. To address this challenge, a novel gene integration system, INTEGRATE, was developed, utilizing CRISPR-mediated transposase technologies for precise genomic insertion within the S. oneidensis MR-1 genome. This system facilitated the insertion of extensive gene segments at different sites of the Shewanella genome with an efficiency approaching 100%. The inserted cargo genes could be kept stable on the genome after continuous cultivation. The enhancement of the organism's EET efficiency was realized through two primary strategies: the integration of the phenazine-1-carboxylic acid synthesis gene cluster to augment EET efficiency and the targeted disruption of the SO3350 gene to promote anodic biofilm development. Collectively, our findings highlight the potential of utilizing the INTEGRATE system for strategic genomic alterations, presenting a synergistic approach to augment the functionality of electroactive bacteria within bioelectrochemical systems.

Jiao Feng, Feng Jia, Chunqiu Li et al.

Frontiers in Microbiology · 2022

Microbial cells utilizing electricity to produce high-value fuels and chemicals are the foundation of the biocathodic bioelectrochemical system. However, molecular mechanisms of electron transfer and utilization have not been elucidated. In this work, Escherichia coli engineered by introducing the Mtr pathway from Shewanella oneidensis exhibited stronger electrochemical activity than control and could utilize exogenous electrons to stimulate metabolite profiles and boost succinate production in the bioelectrochemical system. Proteomic analysis and real-time PCR were performed to investigate the effect of exogenous electrons on electroactive E. coli. Bioinformatics analysis suggested that the proteins of molecular function associated with oxidoreductase activity, 4 iron, 4 sulfur([4Fe-4S]) cluster binding, iron-sulfur cluster binding, and metal cluster binding were positively affected by exogenous electrons. Moreover, mapping to the Kyoto Encyclopedia of Genes and Genomes pathway database showed that the up-regulated proteins were mainly involved in metabolic pathways of tricarboxylic acid cycle, pyruvate metabolism, and nitrogen metabolism pathway, providing support for the metabolic balance of microbial cells shifting toward reduced end-products due to electron utilization. Using a biochemical method, the ompF -overexpressed strain was employed to investigate the function of the channel protein. These findings provided a theoretical basis for further improving electron transfer and utilization efficiency, and contributed to the potential applications of the bioelectrochemical system.

Akiho Matsumoto, Ryota Koga, Robert A. Kanaly et al.

Applied and Environmental Microbiology · 2021

In many bacteria, cyclic diguanosine monophosphate (c-di-GMP), synthesized by diguanylate cyclase (DGC), serves as a second messenger involved in the regulation of biofilm formation. Although studies have suggested that c-di-GMP also regulates the formation of electrochemically active biofilms (EABFs) by Shewanella oneidensis MR-1, DGCs involved in this process remained to be identified. Here, we report that the SO_1646 gene, hereafter named dgcS , is upregulated under medium flow conditions in electrochemical flow cells (EFCs), and its product (DgcS) functions as a major DGC in MR-1. In vitro assays demonstrated that purified DgcS catalyzed the synthesis of c-di-GMP from GTP. Comparisons of intracellular c-di-GMP levels in the wild-type strain and a dgcS deletion mutant (Δ dgcS mutant) showed that production of c-di-GMP was markedly reduced in the Δ dgcS mutant when cells were grown in batch cultures and on electrodes in EFCs. Cultivation of the Δ dgcS mutant in EFCs also revealed that the loss of DgcS resulted in impaired biofilm formation and decreased current generation. These findings demonstrate that MR-1 uses DgcS to synthesize c-di-GMP under medium flow conditions, thereby activating biofilm formation on electrodes. IMPORTANCE Bioelectrochemical systems (BESs) have attracted wide attention owing to their utility in sustainable biotechnology processes, such as microbial fuel cells and electrofermentation systems. In BESs, electrochemically active bacteria (EAB) form biofilms on electrode surfaces, thereby serving as effective catalysts for the interconversion between chemical and electric energy. It is therefore important to understand mechanisms for the formation of biofilm by EAB grown on electrodes. Here, we show that a model EAB, S. oneidensis MR-1, expresses DgcS as a major DGC, thereby activating the formation of biofilms on electrodes via c-di-GMP-dependent signal transduction cascades. The findings presented herein provide the molecular basis for improving electrochemical interactions between EAB and electrodes in BESs. The results also offer molecular insights into how Shewanella regulates biofilm formation on solid surfaces in the natural environment.

Guowei Chen, Rundong Xu, Li Liu et al.

Applied Microbiology and Biotechnology · 2018

Luca Häuser, Johannes Erben, Guillaume Pillot et al.

RSC Advances · 2022

Identifying the limiting processes of electroactive biofilms is key to improve the performance of bioelectrochemical systems (BES). For modelling and developing BES, spatial information of transport phenomena and biofilm distribution are required and can be determined by Magnetic Resonance Imaging (MRI) in vivo , in situ and in operando even inside opaque porous electrodes. A custom bioelectrochemical cell was designed that allows MRI measurements with a spatial resolution of 50 μm inside a 500 μm thick porous carbon electrode. The MRI data showed that only a fraction of the electrode pore space is colonized by the Shewanella oneidensis MR-1 biofilm. The maximum biofilm density was observed inside the porous electrode close to the electrode-medium interface. Inside the biofilm, mass transport by diffusion is lowered down to 45% compared to the bulk growth medium. The presented data and the methods can be used for detailed models of bioelectrochemical systems and for the design of improved electrode structures.

Sindhu K. Suravaram, David K. Smith, Alison Parkin et al.

ChemElectroChem · 2019

Abstract Shewanella oneidensis is an electrogenic microbe which could be more widely applied in biosensing and fuel cell applications if better methods existed to promote electrode‐biofilm formation. This paper reports a simple procedure that converts agarose, a cheap and readily available polymer, into a modified “MAgarose” material which will form biocompatible hydrogels that embed gold nanoparticles (AuNPs) along the fibers to yield a composite material with a conductivity ca. 80 times higher than an unmodified agarose‐AuNP gel. Proof‐of‐concept bioelectrochemical experiments using Shewanella oneidensis show that when these MAgarose‐AuNP gels are used to coat carbon veil there is a 10‐fold increase in oxidative microbial current production when tested in a 3‐electrode cell set‐up. Microscopy results show that this can be attributed to the ability of the composite hydrogel to support MR‐1 growth throughout the 3D matrix.

Yundang Wu, Wei Liu, Tongxu Liu et al.

ChemElectroChem · 2018

Abstract Phenoxazine and quinone are typical electron mediators in natural and engineered systems. Although the electron shuttling process of quinone has been well studied, phenoxazine is poorly characterized. Here, a model phenoxazine (resazurin) was examined as an electron mediator in a bioelectrochemical system with Shewanella oneidensis MR‐1. Results showed that the current generation was substantially enhanced by the presence of phenoxazine, and was almost unaffected even after replacing the original medium with a fresh medium without phenoxazine. This is completely different to the well‐known quinones used as electron mediators. Further study suggested that, resorufin (RR), as an intermediate product, was deposited in situ onto the electrode. The RR deposition was suggested to be a dominant mechanism for stabilizing the electron shuttling efficiency by phenoxazine. This study proposed a novel electron shuttling mechanism of phenoxazine and may provide a new insight into the extracellular electron transfer.

Atsushi Kouzuma

Bioscience Biotechnology and Biochemistry · 2021

Electrochemically active bacteria (EAB) interact electrochemically with electrodes via extracellular electron transfer (EET) pathways. These bacteria have attracted significant attention due to their utility in environmental-friendly bioelectrochemical systems (BESs), including microbial fuel cells and electrofermentation systems. The electrochemical activity of EAB is dependent on their carbon catabolism and respiration; thus, understanding how these processes are regulated will provide insights into the development of a more efficient BES. The process of biofilm formation by EAB on BES electrodes is also important for electric current generation because it facilitates physical and electrochemical interactions between EAB cells and electrodes. This article summarizes the current knowledge on EET-related metabolic and cellular functions of a model EAB, Shewanella oneidensis MR-1, focusing specifically on regulatory systems for carbon catabolism, EET pathways, and biofilm formation. Based on recent developments, the author also discusses potential uses of engineered S. oneidensis strains for various biotechnological applications.

Qinran Ding, Qijing Liu, Yan Zhang et al.

ACS Synthetic Biology · 2022

Efficient extracellular electron transfer (EET) of exoelectrogens is critical for practical applications of various bioelectrochemical systems. However, the low efficiency of electron transfer remains a major bottleneck. In this study, a modular engineering strategy, including broadening the sources of the intracellular electron pool, enhancing intracellular nicotinamide adenine dinucleotide (NADH) regeneration, and promoting electron release from electron pools, was developed to redirect electron flux into the electron transfer chain in Shewanella oneidensis MR-1. Among them, four genes include gene SO1522 encoding a lactate transporter for broadening the sources of the intracellular electron pool, gene gapA encoding a glyceraldehyde-3-phosphate dehydrogenase and gene mdh encoding a malate dehydrogenase in the central carbon metabolism for enhancing intracellular NADH regeneration, and gene ndh encoding NADH dehydrogenase on the inner membrane for releasing electrons from intracellular electron pools into the electron-transport chain. Upon assembly of the four genes, electron flux was directly redirected from the electron donor to the electron-transfer chain, achieving 62% increase in intracellular NADH levels, which resulted in a 3.5-fold enhancement in the power density from 59.5 ± 3.2 mW/m 2 (wild type) to 270.0 ± 12.7 mW/m 2 (recombinant strain). This study confirmed that redirecting electron flux from the electron donor to the electron-transfer chain is a viable approach to enhance the EET rate of S. oneidensis .

Ning Xu, Tai-Lin Wang, Wenjie Li et al.

Frontiers in Bioengineering and Biotechnology · 2021

Bioelectrochemical systems (BESs) are emerging as attractive routes for sustainable energy generation, environmental remediation, bio-based chemical production and beyond. Electron shuttles (ESs) can be reversibly oxidized and reduced among multiple redox reactions, thereby assisting extracellular electron transfer (EET) process in BESs. Here, we explored the effects of 14 ESs on EET in Shewanella oneidensis MR-1, and found that anthraquinone-2-sulfonate (AQS) led to the highest cathodic current density, total charge production and reduction product formation. Subsequently, we showed that the introduction of -OH or -NH 2 group into AQS at position one obviously affected redox potentials. The AQS-1-NH 2 exhibited a lower redox potential and a higher Coulombic efficiency compared to AQS, revealing that the ESs with a more negative potential are conducive to minimize energy losses and improve the reduction of electron acceptor. Additionally, the cytochromes MtrA and MtrB were required for optimal AQS-mediated EET of S. oneidensis MR-1. This study will provide new clues for rational design of efficient ESs in microbial electrosynthesis.

Jiao Feng, Mingjun Jiang, Kang Li et al.

Bioelectrochemistry · 2020

Xiang Qi, Shuyi Wang, Yong Jiang et al.

Water Research · 2021

Boyu Jia, Tianbao Liu, Juanjuan Wan et al.

Environmental Research · 2022

Peter Lamberg, Kara L. Bren

ACS Energy Letters · 2016

Carbon paste paper electrodes (CPPEs) were fabricated by coating a regular paper strip with carbon paste made from graphite powder and mineral oil, followed by coating with polyaniline. The CPPEs were evaluated as anodes in bioelectrochemical cells (BECs) using Shewanella oneidensis MR-1 as bacteria that donate electrons through extracellular electron transfer. The CPPE was compared to a carbon felt electrode (CFE) modified with polyaniline under the same conditions. The BEC using the CPPE anode produces current continuously for at least 4 days without the need for additional fuel (lactate). Twenty-four hours after inoculation, the BEC using the CPPE anode generates a current density more than two times greater than that of the cell using the CFE, with a competitive maximum value of 2.2 A m–2. The simple fabrication, ease of modification, and low cost of the CPPE make it a promising new bioelectrode material for microbial fuel cells.

Yixuan Wang, Wenqiang Li, Chuan-Shu He et al.

Biosensors and Bioelectronics · 2020

Beum Jun Kim, Injun Chu, Sebastian Jusuf et al.

Frontiers in Microbiology · 2016

Shewanella oneidensis is a model bacterial strain for studies of bioelectrochemical systems (BESs). It has two extracellular electron transfer pathways: (1) shuttling electrons via an excreted mediator riboflavin; and (2) direct contact between the c -type cytochromes at the cell membrane and the electrode. Despite the extensive use of S. oneidensis in BESs such as microbial fuel cells and biosensors, many basic microbiology questions about S. oneidensis in the context of BES remain unanswered. Here, we present studies of motility and chemotaxis of S. oneidensis under well controlled concentration gradients of two electron acceptors, oxygen and oxidized form of riboflavin (flavin+), using a newly developed microfluidic platform. Experimental results demonstrate that either oxygen or flavin+ is a chemoattractant to S. oneidensis. The chemotactic tendency of S. oneidensis in a flavin+ concentration gradient is significantly enhanced in an anaerobic in contrast to an aerobic condition. Furthermore, either a low oxygen tension or a high flavin+ concentration considerably enhances the speed of S. oneidensis. This work presents a robust microfluidic platform for generating oxygen and/or flavin+ gradients in an aqueous environment, and demonstrates that two important electron acceptors, oxygen and oxidized riboflavin, cooperatively regulate S. oneidensis migration patterns. The microfluidic tools presented as well as the knowledge gained in this work can be used to guide the future design of BESs for efficient electron production.

Yanan Fu, Yongjia Zhang, Bojian Li et al.

Electrochimica Acta · 2019

Yixuan Wang, Wenqiang Li, Chuan-Shu He et al.

Journal of Cleaner Production · 2020

Ariel L. Furst, Matthew J. Smith, Michael C. Lee et al.

ACS Central Science · 2018

As fossil fuels are increasingly linked to environmental damage, the development of renewable, affordable biological alternative fuels is vital. Shewanella oneidensis is often suggested as a potential component of bioelectrochemical cells because of its ability to act as an electron donor to metal surfaces. These microbes remain challenging to implement, though, due to inconsistency in biofilm formation on electrodes and therefore current generation. We have applied DNA hybridization-based cell adhesion to immobilize S. oneidensis on electrodes. High levels of current are reproducibly generated from these cell layers following only 30 min of immobilization without the need for the formation of a biofilm. Upon incorporation of DNA mismatches in the microbe immobilization sequence, significant attenuation in current production is observed, suggesting that at least part of the electron transfer to the electrode is DNA-mediated. This method of microbe assembly is rapid, reproducible, and facile for the production of anodes for biofuel cells.

Verónica Delgado, Catarina M. Paquete, Gunnar Sturm et al.

Bioelectrochemistry · 2019

Tutut Arinda, Laura-Alina Philipp, David Rehnlund et al.

Frontiers in Microbiology · 2019

Shewanella oneidensis is one of the best-understood model organisms for extracellular electron transfer. Endogenously produced and exported flavin molecules seem to play an important role in this process and mediate the connection between respiratory enzymes on the cell surface and the insoluble substrate by acting as electron shuttle and cytochrome-bound cofactor. Consequently, the addition of riboflavin to a bioelectrochemical system (BES) containing S. oneidensis cells as biocatalyst leads to a strong current increase. Still, an external application of riboflavin to increase current production in continuously operating bioelectrochemical systems does not seem to be applicable due to the constant washout of the soluble flavin compound. In this study, we developed a recyclable electron shuttle to overcome the limitation of mediator addition to BES. Riboflavin was coupled to magnetic beads that can easily be recycled from the medium. The effect on current production and cell distribution in a BES as well as the recovery rate and the stability of the beads was investigated. The addition of synthesized beads leads to a more than 2-fold higher current production, which was likely caused by increased biofilm production. Moreover, 90% of the flavin-coupled beads could be recovered from the bioelectrochemical systems using a magnetic separator.

Yundang Wu, Xiaobo Luo, Baoli Qin et al.

Environmental Science & Technology · 2020

Exogenous electron mediators (EMs) can facilitate extracellular electron transfer (EET) via electron shuttling processes, but it is still unclear whether and how biofilm formation is affected by the presence of EMs. Here, the impacts of EMs on EET and biofilm formation were investigated in bioelectrochemical systems (BESs) with Shewanella oneidensis MR-1, and the results showed that the presence of five different EMs led to high density current production. All the EMs substantially promoted biofilm formation with 15-36 times higher total biofilm DNA with EMs than without EMs, and they also increased the production of extracellular polymeric substances, which was favorable for biofilm formation. The current decreased substantially after removing EMs from the medium or by replacing electrodes without biofilm, suggesting that both biofilm and EMs are required for high density current production. EET-related gene expression was upregulated with EMs, resulting in the high flux of cell electron output. A synergistic mechanism was proposed: EMs in suspension were quickly reduced by the cells and reoxidized rapidly by the electrode, resulting in a microenvironment with sufficient oxidized EMs for biofilm formation, and thus, besides the well-known electron shuttling process, the EM-induced high biofilm formation and high Mtr gene expression could jointly contribute to the EET and subsequently produce a high density current. This study provides a new insight into EM-enhanced current production via regulating the biofilm formation and EET-related gene expression.

Rong-Wei Si, Yuan Yang, Yangyang Yu et al.

Analytical Chemistry · 2016

A whole-cell bioelectrochemical biosensing system for amperometric detection of riboflavin was developed. A "bioelectrochemical wire" (BW) consisting of riboflavin and cytochrome C between Shewanella oneidensis MR-1 and electrode was characterized. Typically, a strong electrochemical response was observed when riboflavin (VB2) was added to reinforce this BW. Impressively, the electrochemical response of riboflavin with this BW was over 200 times higher than that without bacteria. Uniquely, this electron rewiring process enabled the development of a biosensing system for amperometric detection of riboflavin. Remarkably, this amperometric method showed high sensitivity (LOD = 2.2 nM, S/N = 3), wide linear range (5 nM ∼ 10 μM, 3 orders of magnitude), good selectivity, and high resistance to interferences. Additionally, the developed amperometric method featured good stability and reusability. It was further applied for accurate and reliable determination of riboflavin in real conditions including food, pharmaceutical, and clinical samples without pretreatment. Both the cost-effectiveness and robustness make this whole-cell amperometric system ideal for practical applications. This work demonstrated the power of bioelectrochemical signal amplification with exoelectrogen and also provided a new idea for development of versatile whole-cell amperometric biosensors.

Yuan Yang, Yangyang Yu, Yan‐Zhai Wang et al.

Biosensors and Bioelectronics · 2017

Yixin Li, Jiaying Su, Ruixiang Zhao et al.

Chemical Engineering Science · 2024

Sahand Pirbadian, Marko S. Chavez, Mohamed Y. El‐Naggar

Proceedings of the National Academy of Sciences · 2020

Extracellular electron transfer (EET) allows microorganisms to gain energy by linking intracellular reactions to external surfaces ranging from natural minerals to the electrodes of bioelectrochemical renewable energy technologies. In the past two decades, electrochemical techniques have been used to investigate EET in a wide range of microbes, with emphasis on dissimilatory metal-reducing bacteria, such as Shewanella oneidensis MR-1, as model organisms. However, due to the typically bulk nature of these techniques, they are unable to reveal the subpopulation variation in EET or link the observed electrochemical currents to energy gain by individual cells, thus overlooking the potentially complex spatial patterns of activity in bioelectrochemical systems. Here, to address these limitations, we use the cell membrane potential as a bioenergetic indicator of EET by S. oneidensis MR-1 cells. Using a fluorescent membrane potential indicator during in vivo single-cell-level fluorescence microscopy in a bioelectrochemical reactor, we demonstrate that membrane potential strongly correlates with EET. Increasing electrode potential and associated EET current leads to more negative membrane potential. This EET-induced membrane hyperpolarization is spatially limited to cells in contact with the electrode and within a near-electrode zone (<30 μm) where the hyperpolarization decays with increasing cell-electrode distance. The high spatial and temporal resolution of the reported technique can be used to study the single-cell-level dynamics of EET not only on electrode surfaces, but also during respiration of other solid-phase electron acceptors.

De-Zhen Sun, Yangyang Yu, Rongrong Xie et al.

Biosensors and Bioelectronics · 2016

Lang Chen, Yang Wu, Qiuting Shen et al.

Bioresource Technology · 2022

А. А. Самков, Yu. A. Chugunova, M. N. Kruglova et al.

Applied Biochemistry and Microbiology · 2023

The effect of the polarity of the electrical stimulation of the external circuit of the bioelectrochemical systems, as well as the immobilization of Shewanella oneidensis MR-1 cells containing the DyP peroxidase gene on the rate of discoloration of dyes of different types, was found. For the crystal violet triphenylmethane dye, the maximum decolorization rate by suspended S. oneidensis MR-1 cells of 2.05 ± 0.07 μM/h was noted when connecting a 1.2 V direct polarity DC voltage source. One of the minimum rates was observed with reverse polarity of the connection. For cells immobilized on the anode, the rate was higher, reaching 2.91 ± 0.09 μM/h and did not decrease with increasing substrate concentration. The lowest values were also noted for the reverse connection of the voltage source. For the azo dye congo red, the maximum rate was found for a source with direct connection and an open circuit (0.26 ± 0.01 and 0.29 ± 0.02 μM/h, respectively); the minimum value was 0.11 ± 0.02 μM/h for a reverse connection. For crystal violet decolorization products, a significant decrease in the intensity of the main absorption peak at 590 nm band was found, with no notable hypsochromic shift. The qualitative changes in the decolorization product composition were indicated by the appearance, with a direct polarity of the ionistor connection, of a new absorption maximum in the region of 360 nm. The results may be of interest for the development of new methods of bioelectrochemical cleaning.

Atsumi Hirose, Atsushi Kouzuma, Kazuya Watanabe

Journal of Bioscience and Bioengineering · 2020

Haoran Yuan, Lifang Deng, Xin Qian et al.

The Science of The Total Environment · 2019

Shu-Hong Gao, Lai Peng, Yiwen Liu et al.

International Biodeterioration & Biodegradation · 2016

Takuya Kasai, Yuki Tomioka, Atsushi Kouzuma et al.

Bioelectrochemistry · 2019

Nweze Julius Eyiuche, Shiho Asakawa, Takahiro Yamashita et al.

BMC Microbiology · 2017

Anodic community structure was dependent on both substrate and anode material. Although Desulfuromonas spp. are marine microorganisms, they were abundant in the acetate-fed community on FO-SSA, implying the presence of novel non-halophilic and exoelectrogenic species in this genus. Power generation using FO-SSA was positively related to the frequency of exoelectrogenic genera in the anodic community. Predominant LAB in saccharide-fed anodic biofilm caused low abundance of exoelectrogenic genera and consequent low power generation.

Meriem Saadi, Julien Pézard, Naoufel Haddour et al.

Materials Research Express · 2020

Abstract Modification of electrode surfaces is a promising strategy to improve microbial fuel cell (MFC) performance. Here we report a new functionalization process to improve interfacial electron transfer, biocompatibility and corrosion resistance of stainless steel (SS) electrodes used as anodes in MFCs. SS anodes prepared by surface modification with a thin layer (200 μ m) of conducting composite made of polydimethylsiloxane (PDMS) doped with commercially available carbon nanofibers (CNF), are described. Electrochemical characterization showed that the corrosion rate of SS electrode in an acid solution decreased from 367 μ m.y −1 to 31 μ m.y −1 after CNF-PDMS coating. Electric characterization demonstrated that the maximum power density generated by MFCs after 16 days with SS/CNF-PDMS anodes (19 mW.m −2 ) is 5 times higher and more stable than that with unmodified SS (3.7 mW.m −2 ). The cyclic voltammetry analysis indicated that the electrochemical activity of the modified anode was enhanced significantly after 16 days and the electron transfer was facilitated by CNF-PDMS modification. Microscopic observations and electrochemical characterization showed that CNF-PDMS composite improved biocompatibility and corrosion resistance of the SS anode surfaces. These results confirmed that the CNF-PDMS modification is a promising approach to improve the properties of anode materials for MFC application.

Sarah K. Springthorpe, Christopher M. Dundas, Benjamin K. Keitz

Nature Communications · 2019

Redox interactions between electroactive bacteria and inorganic materials underpin many emerging technologies, but commonly used materials (e.g., metal oxides) suffer from limited tunability and can be challenging to characterize. In contrast, metal-organic frameworks exhibit well-defined structures, large surface areas, and extensive chemical tunability, but their utility as microbial substrates has not been examined. Here, we report that metal-organic frameworks can support the growth of the metal-respiring bacterium Shewanella oneidensis, specifically through the reduction of Fe(III). In a practical application, we show that cultures containing S. oneidensis and reduced metal-organic frameworks can remediate lethal concentrations of Cr(VI) over multiple cycles, and that pollutant removal exceeds the performance of either component in isolation or bio-reduced iron oxides. Our results demonstrate that frameworks can serve as growth substrates and suggest that they may offer an alternative to metal oxides in applications seeking to combine the advantages of bacterial metabolism and synthetic materials.

Gianni F. Vettese, Katherine Morris, Louise S. Natrajan et al.

Environmental Science & Technology · 2020

As the dominant radionuclide by mass in many radioactive wastes, the control of uranium mobility in contaminated environments is of high concern. U speciation can be governed by microbial interactions, whereby metal-reducing bacteria are able to reduce soluble U(VI) to insoluble U(IV), providing a method for removal of U from contaminated groundwater. Although microbial U(VI) reduction is widely reported, the mechanism(s) for the transformation of U(VI) to relatively insoluble U(IV) phases are poorly understood. By combining a suite of analyses, including luminescence, U M 4 -edge high-energy resolved fluorescence detection-X-ray absorption near-edge structure (XANES), and U L 3 -edge XANES/extended X-ray absorption fine structure, we show that the microbial reduction of U(VI) by the model Fe(III)-reducing bacterium, Shewanella oneidensis MR1, proceeds via a single electron transfer to form a pentavalent U(V) intermediate which disproportionates to form U(VI) and U(IV). Furthermore, we have identified significant U(V) present in post reduction solid phases, implying that U(V) may be stabilized for up to 120.5 h.

Jie Jiang, Pengchen He, Ying Luo et al.

Frontiers in Microbiology · 2023

Geobacter sulfurreducens mediates extracellular electron transfer (EET) reactions with different substrates, such as solid-phase Fe(III)-containing minerals, anodes and the cells of Geobacter metallireducens . To compare their roles in EET, the pilA-N, omcE , omcS , omcT and omcZ genes of G. sulfurreducens were systematically deleted. All mutants showed impaired and varied ability to form biofilms on nonconductive surface. Deletion of omcE also impaired bacterial ability to reduce ferrihydrite, but its impacts on the ability for anode reduction and the co-culture of G. metallireducens - G. sulfurreducens were minimal. The mutant without omcS showed diminished ability to reduce ferrihydrite and to form the co-culture, but was able to regain its ability to reduce anodes. Deletion of omcT , omcZ or pilA-N alone impaired bacterial ability to reduce ferrihydrite and anodes and to form the co-culture. Deletion of all tested genes abolished bacterial ability to reduce ferrihydrite and anodes. Triple-deletion of all omcS, omcT and omcZ abolished the ability of G. sulfurreducens to co-culture with G. metallireducens . However, deletion of only omcZ or pilA-N or both omcS and omcT abolished the ability of G. sulfurreducens without hydrogenase gene hybL to co-culture with G. metallireducens , which show their indispensable roles in direct electron transfer from G. metallireducens to G. sulfurreducens . Thus, the roles of pilA-N, omcE , omcS , omcT and omcZ for G. sulfurreducens in EET vary substantially, which also suggest that possession of PilA-N and multiple cytochromes of different structures enables G. sulfurreducens to mediate EET reactions efficiently with substrates of different properties.