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Alarcon HV, Mohl JE, Chong GW, Betancourt A, Wang Y, Leng W, White JC, Xu J. Evidence for autotrophic growth of purple sulfur bacteria using pyrite as electron and sulfur source. Appl Environ Microbiol 2024:e0086324. [PMID: 38899885 DOI: 10.1128/aem.00863-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2024] [Accepted: 05/22/2024] [Indexed: 06/21/2024] Open
Abstract
Purple sulfur bacteria (PSB) are capable of anoxygenic photosynthesis via oxidizing reduced sulfur compounds and are considered key drivers of the sulfur cycle in a range of anoxic environments. In this study, we show that Allochromatium vinosum (a PSB species) is capable of autotrophic growth using pyrite as the electron and sulfur source. Comparative growth profile, substrate characterization, and transcriptomic sequencing data provided valuable insight into the molecular mechanisms underlying the bacterial utilization of pyrite and autotrophic growth. Specifically, the pyrite-supported cell cultures ("py"') demonstrated robust but much slower growth rates and distinct patterns from their sodium sulfide-amended positive controls. Up to ~200-fold upregulation of genes encoding various c- and b-type cytochromes was observed in "py," pointing to the high relevance of these molecules in scavenging and relaying electrons from pyrite to cytoplasmic metabolisms. Conversely, extensive downregulation of genes related to LH and RC complex components indicates that the electron source may have direct control over the bacterial cells' photosynthetic activity. In terms of sulfur metabolism, genes encoding periplasmic or membrane-bound proteins (e.g., FccAB and SoxYZ) were largely upregulated, whereas those encoding cytoplasmic proteins (e.g., Dsr and Apr groups) are extensively suppressed. Other notable differentially expressed genes are related to flagella/fimbriae/pilin(+), metal efflux(+), ferrienterochelin(-), and [NiFe] hydrogenases(+). Characterization of the biologically reacted pyrite indicates the presence of polymeric sulfur. These results have, for the first time, put the interplay of PSB and transition metal sulfide chemistry under the spotlight, with the potential to advance multiple fields, including metal and sulfur biogeochemistry, bacterial extracellular electron transfer, and artificial photosynthesis. IMPORTANCE Microbial utilization of solid-phase substrates constitutes a critical area of focus in environmental microbiology, offering valuable insights into microbial metabolic processes and adaptability. Recent advancements in this field have profoundly deepened our knowledge of microbial physiology pertinent to these scenarios and spurred innovations in biosynthesis and energy production. Furthermore, research into interactions between microbes and solid-phase substrates has directly linked microbial activities to the surrounding mineralogical environments, thereby enhancing our understanding of the relevant biogeochemical cycles. Our study represents a significant step forward in this field by demonstrating, for the first time, the autotrophic growth of purple sulfur bacteria using insoluble pyrite (FeS2) as both the electron and sulfur source. The presented comparative growth profiles, substrate characterizations, and transcriptomic sequencing data shed light on the relationships between electron donor types, photosynthetic reaction center activities, and potential extracellular electron transfer in these organisms capable of anoxygenic photosynthesis. Furthermore, the findings of our study may provide new insights into early-Earth biogeochemical evolutions, offering valuable constraints for understanding the environmental conditions and microbial processes that shaped our planet's history.
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Affiliation(s)
- Hugo V Alarcon
- Environmental Science and Engineering Program, the University of Texas at El Paso, El Paso, Texas, USA
| | - Jonathon E Mohl
- Department of Mathematical Sciences, the University of Texas at El Paso, El Paso, Texas, USA
- Border Biomedical Research Center, the University of Texas at El Paso, El Paso, Texas, USA
| | - Grace W Chong
- Department of Earth, Environmental and Resource Sciences, the University of Texas at El Paso, El Paso, Texas, USA
| | - Ana Betancourt
- Border Biomedical Research Center, the University of Texas at El Paso, El Paso, Texas, USA
| | - Yi Wang
- The Connecticut Agricultural Experiment Station, New Haven, Connecticut, USA
| | - Weinan Leng
- The National Center for Earth and Environmental Nanotechnology Infrastructure, Blacksburg, Virginia, USA
| | - Jason C White
- The Connecticut Agricultural Experiment Station, New Haven, Connecticut, USA
| | - Jie Xu
- Environmental Science and Engineering Program, the University of Texas at El Paso, El Paso, Texas, USA
- Department of Earth, Environmental and Resource Sciences, the University of Texas at El Paso, El Paso, Texas, USA
- School of Molecular Sciences, Arizona State University, Tempe, Arizona, USA
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2
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van Wonderen JH, Crack JC, Edwards MJ, Clarke TA, Saalbach G, Martins C, Butt JN. Liquid-chromatography mass spectrometry describes post-translational modification of Shewanella outer membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184221. [PMID: 37673350 DOI: 10.1016/j.bbamem.2023.184221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 08/09/2023] [Accepted: 08/30/2023] [Indexed: 09/08/2023]
Abstract
Electrogenic bacteria deliver excess respiratory electrons to externally located metal oxide particles and electrodes. The biochemical basis for this process is arguably best understood for species of Shewanella where the integral membrane complex termed MtrCAB is key to electron transfer across the bacterial outer membranes. A crystal structure was recently resolved for MtrCAB from S. baltica OS185. However, X-ray diffraction did not resolve the N-terminal residues so that the lipidation status of proteins in the mature complex was poorly described. Here we report liquid chromatography mass spectrometry revealing the intact mass values for all three proteins in the MtrCAB complexes purified from Shewanella oneidensis MR-1 and S. baltica OS185. The masses of MtrA and MtrB are consistent with both proteins being processed by Signal Peptidase I and covalent attachment of ten c-type hemes to MtrA. The mass of MtrC is most reasonably interpreted as arising from protein processed by Signal Peptidase II to produce a diacylated lipoprotein containing ten c-type hemes. Our two-step protocol for liquid-chromatography mass spectrometry used a reverse phase column to achieve on-column detergent removal prior to gradient protein resolution and elution. We envisage the method will be capable of simultaneously resolving the intact mass values for multiple proteins in other membrane protein complexes.
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Affiliation(s)
- Jessica H van Wonderen
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
| | - Jason C Crack
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Marcus J Edwards
- School of Biological Sciences, University of East Anglia, , Norwich Research Park, Norwich NR4 7TJ, UK; School of Life Sciences, University of Essex, Colchester CO4 3SQ, UK
| | - Thomas A Clarke
- School of Biological Sciences, University of East Anglia, , Norwich Research Park, Norwich NR4 7TJ, UK
| | - Gerhard Saalbach
- Proteomics Facility, The John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
| | - Carlo Martins
- Proteomics Facility, The John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
| | - Julea N Butt
- School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK; School of Biological Sciences, University of East Anglia, , Norwich Research Park, Norwich NR4 7TJ, UK.
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Rastkhah E, Fatemi F, Maghami P. Optimizing the Metal Bioreduction Process in Recombinant Shewanella azerbaijanica Bacteria: A Novel Approach via mtrC Gene Cloning and Nitrate-Reducing Pathway Destruction. Mol Biotechnol 2023:10.1007/s12033-023-00920-x. [PMID: 37917324 DOI: 10.1007/s12033-023-00920-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Accepted: 09/22/2023] [Indexed: 11/04/2023]
Abstract
Environmental pollution is growing every day in terms of the increase in population, industrialization, and urbanization. Shewanella azerbaijanica is introduced as a highly potent bacterium in metal bioremediation. The mtrC gene was selected as a cloning target to improve electron flux chains in the EET (extracellular electron transfer) pathway. Using the SDM (site-directed mutagenesis) technique, the unique gene assembly featured the mtrC gene sandwiched between two napD/B genes to disrupt the nitrate reduction pathway, which serves as the primary metal reduction competitor. Shew-mtrC gene construction was transferred to expression plasmid pET28a (+) in the expression host bacteria (E. coli BL21 and S. azerbaijanica), in pUC57, cloning plasmid, which was transferred to the cloning host bacteria E. coli Top10 and S. azerbaijanica. All cloning procedures (i.e., synthesis, insertion, transformation, cloning, and protein expression) were verified and confirmed by precise tests. ATR-FTIR analysis, CD, western blotting, affinity chromatography, SDS-PAGE, and other techniques were used to confirm the expression and structure of the MtrC protein. The genome sequence and primers were designed according to the submitted Shewanella oneidensis MR-1 genome, the most similar bacteria to this native species. The performance of recombinant S. azerbaijanica bacterium in metal bioremediation, as sustainable strategy, has to be verified by more research.
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Affiliation(s)
- Elham Rastkhah
- Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran
| | - Faezeh Fatemi
- Nuclear Fuel Cycle Research School, Nuclear Science and Technology Research Institute, Tehran, Iran.
| | - Parvaneh Maghami
- Department of Biology, Science and Research Branch, Islamic Azad University, Tehran, Iran
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Abstract
Extracellular electron transfer (EET) is the physiological process that enables the reduction or oxidation of molecules and minerals beyond the surface of a microbial cell. The first bacteria characterized with this capability were Shewanella and Geobacter, both reported to couple their growth to the reduction of iron or manganese oxide minerals located extracellularly. A key difference between EET and nearly every other respiratory activity on Earth is the need to transfer electrons beyond the cell membrane. The past decade has resolved how well-conserved strategies conduct electrons from the inner membrane to the outer surface. However, recent data suggest a much wider and less well understood collection of mechanisms enabling electron transfer to distant acceptors. This review reflects the current state of knowledge from Shewanella and Geobacter, specifically focusing on transfer across the outer membrane and beyond-an activity that enables reduction of highly variable minerals, electrodes, and even other organisms.
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Affiliation(s)
- J A Gralnick
- BioTechnology Institute and Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA; ,
| | - D R Bond
- BioTechnology Institute and Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA; ,
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5
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Recent Applications and Strategies to Enhance Performance of Electrochemical Reduction of CO2 Gas into Value-Added Chemicals Catalyzed by Whole-Cell Biocatalysts. Processes (Basel) 2023. [DOI: 10.3390/pr11030766] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023] Open
Abstract
Carbon dioxide (CO2) is one of the major greenhouse gases that has been shown to cause global warming. Decreasing CO2 emissions plays an important role to minimize the impact of climate change. The utilization of CO2 gas as a cheap and sustainable source to produce higher value-added chemicals such as formic acid, methanol, methane, and acetic acid has been attracting much attention. The electrochemical reduction of CO2 catalyzed by whole-cell biocatalysts is a promising process for the production of value-added chemicals because it does not require costly enzyme purification steps and the supply of exogenous cofactors such as NADH. This study covered the recent applications of the diversity of microorganisms (pure cultures such as Shewanella oneidensis MR1, Sporomusa species, and Clostridium species and mixed cultures) as whole-cell biocatalysts to produce a wide range of value-added chemicals including methane, carboxylates (e.g., formate, acetate, butyrate, caproate), alcohols (e.g., ethanol, butanol), and bioplastics (e.g., Polyhydroxy butyrate). Remarkably, this study provided insights into the molecular levels of the proteins/enzymes (e.g., formate hydrogenases for CO2 reduction into formate and electron-transporting proteins such as c-type cytochromes) of microorganisms which are involved in the electrochemical reduction of CO2 into value-added chemicals for the suitable application of the microorganism in the chemical reduction of CO2 and enhancing the catalytic efficiency of the microorganisms toward the reaction. Moreover, this study provided some strategies to enhance the performance of the reduction of CO2 to produce value-added chemicals catalyzed by whole-cell biocatalysts.
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Fan Y, Tang Q, Sun H, Yu H. A designed plasmid‐transition strategy enables rapid construction of robust and versatile synthetic exoelectrogens for environmental applications. Environ Microbiol 2022; 24:5292-5305. [DOI: 10.1111/1462-2920.16181] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 08/21/2022] [Indexed: 11/30/2022]
Affiliation(s)
- Yang‐Yang Fan
- CAS Key Laboratory of Urban Pollutant Conversion, School of Life Sciences University of Science and Technology of China Hefei China
- Department of Environmental Science and Engineering University of Science & Technology of China Hefei China
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Institutes of Physical Science and Information Technology Anhui University Hefei China
| | - Qiang Tang
- Department of Environmental Science and Engineering University of Science & Technology of China Hefei China
| | - Hong Sun
- CAS Key Laboratory of Urban Pollutant Conversion, School of Life Sciences University of Science and Technology of China Hefei China
- Department of Environmental Science and Engineering University of Science & Technology of China Hefei China
| | - Han‐Qing Yu
- Department of Environmental Science and Engineering University of Science & Technology of China Hefei China
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7
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Single molecule tracking of bacterial cell surface cytochromes reveals dynamics that impact long-distance electron transport. Proc Natl Acad Sci U S A 2022; 119:e2119964119. [PMID: 35503913 PMCID: PMC9171617 DOI: 10.1073/pnas.2119964119] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Multiheme cytochromes in Shewanella oneidensis MR-1 transport electrons across the cell wall, in a process called extracellular electron transfer. These electron conduits can also enable electron transport along and between cells. While the underlying mechanism is thought to involve a combination of electron hopping and lateral diffusion of cytochromes along membranes, these diffusive dynamics have never been observed in vivo. Here, we observe the mobility of quantum dot-labeled cytochromes on living cell surfaces and membrane nanowires, quantify their diffusion with single-particle tracking techniques, and simulate the contribution of these dynamics to electron transport. This work reveals the impact of redox molecule dynamics on bacterial electron transport, with implications for understanding and harnessing this process in the environment and bioelectronics. Using a series of multiheme cytochromes, the metal-reducing bacterium Shewanella oneidensis MR-1 can perform extracellular electron transfer (EET) to respire redox-active surfaces, including minerals and electrodes outside the cell. While the role of multiheme cytochromes in transporting electrons across the cell wall is well established, these cytochromes were also recently found to facilitate long-distance (micrometer-scale) redox conduction along outer membranes and across multiple cells bridging electrodes. Recent studies proposed that long-distance conduction arises from the interplay of electron hopping and cytochrome diffusion, which allows collisions and electron exchange between cytochromes along membranes. However, the diffusive dynamics of the multiheme cytochromes have never been observed or quantified in vivo, making it difficult to assess their hypothesized contribution to the collision-exchange mechanism. Here, we use quantum dot labeling, total internal reflection fluorescence microscopy, and single-particle tracking to quantify the lateral diffusive dynamics of the outer membrane-associated decaheme cytochromes MtrC and OmcA, two key components of EET in S. oneidensis. We observe confined diffusion behavior for both quantum dot-labeled MtrC and OmcA along cell surfaces (diffusion coefficients DMtrC = 0.0192 ± 0.0018 µm2/s, DOmcA = 0.0125 ± 0.0024 µm2/s) and the membrane extensions thought to function as bacterial nanowires. We find that these dynamics can trace a path for electron transport via overlap of cytochrome trajectories, consistent with the long-distance conduction mechanism. The measured dynamics inform kinetic Monte Carlo simulations that combine direct electron hopping and redox molecule diffusion, revealing significant electron transport rates along cells and membrane nanowires.
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8
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Zhao J, Li F, Cao Y, Zhang X, Chen T, Song H, Wang Z. Microbial extracellular electron transfer and strategies for engineering electroactive microorganisms. Biotechnol Adv 2020; 53:107682. [PMID: 33326817 DOI: 10.1016/j.biotechadv.2020.107682] [Citation(s) in RCA: 73] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 11/04/2020] [Accepted: 12/09/2020] [Indexed: 11/27/2022]
Abstract
Electroactive microorganisms (EAMs) are ubiquitous in nature and have attracted considerable attention as they can be used for energy recovery and environmental remediation via their extracellular electron transfer (EET) capabilities. Although the EET mechanisms of Shewanella and Geobacter have been rigorously investigated and are well characterized, much less is known about the EET mechanisms of other microorganisms. For EAMs, efficient EET is crucial for the sustainable economic development of bioelectrochemical systems (BESs). Currently, the low efficiency of EET remains a key factor in limiting the development of BESs. In this review, we focus on the EET mechanisms of different microorganisms, (i.e., bacteria, fungi, and archaea). In addition, we describe in detail three engineering strategies for improving the EET ability of EAMs: (1) enhancing transmembrane electron transport via cytochrome protein channels; (2) accelerating electron transport via electron shuttle synthesis and transmission; and (3) promoting the microbe-electrode interface reaction via regulating biofilm formation. At the end of this review, we look to the future, with an emphasis on the cross-disciplinary integration of systems biology and synthetic biology to build high-performance EAM systems.
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Affiliation(s)
- Juntao Zhao
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
| | - Feng Li
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
| | - Yingxiu Cao
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
| | - Xinbo Zhang
- Joint Research Centre for Protective Infrastructure Technology and Environmental Green Bioprocess, Department of Environmental and Municipal Engineering, Tianjin Chengjian University, Tianjin 300384, People's Republic of China
| | - Tao Chen
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
| | - Hao Song
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China
| | - Zhiwen Wang
- Frontier Science Center for Synthetic Biology and Key Laboratory of Systems Bioengineering (Ministry of Education), SynBioResearch Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People's Republic of China.
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9
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Dietrich HM, Edel M, Bursac T, Meier M, Sturm-Richter K, Gescher J. Soluble versions of outer membrane cytochromes function as exporters for heterologously produced cargo proteins. Microb Cell Fact 2019; 18:216. [PMID: 31870378 PMCID: PMC6929479 DOI: 10.1186/s12934-019-1270-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 12/13/2019] [Indexed: 11/13/2022] Open
Abstract
This study reveals that it is possible to secrete truncated versions of outer membrane cytochromes into the culture supernatant and that these proteins can provide a basis for the export of heterologously produced proteins. Different soluble and truncated versions of the outer membrane cytochrome MtrF were analyzed for their suitability to be secreted. A protein version with a very short truncation of the N-terminus to remove the recognition sequence for the addition of a lipid anchor is secreted efficiently to the culture supernatant, and moreover this protein could be further truncated by a deletion of 160 amino acid and still is detectable in the supernatant. By coupling a cellulase to this soluble outer membrane cytochrome, the export efficiency was measured by means of relative cellulase activity. We conclude that outer membrane cytochromes of S. oneidensis can be applied as transporters for the export of target proteins into the medium using the type II secretion pathway.
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Affiliation(s)
- Helge M Dietrich
- Department of Molecular Microbiology and Bioenergetics, Goethe University, Frankfurt, Germany
| | - Miriam Edel
- Department of Applied Biology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Thea Bursac
- Department of Applied Biology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Manfred Meier
- Institute for Biological Interfaces, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany
| | - Katrin Sturm-Richter
- Department of Applied Biology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
| | - Johannes Gescher
- Department of Applied Biology, Institute for Applied Biosciences, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
- Institute for Biological Interfaces, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.
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10
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Le QAT, Kim HG, Kim YH. Electrochemical synthesis of formic acid from CO2 catalyzed by Shewanella oneidensis MR-1 whole-cell biocatalyst. Enzyme Microb Technol 2018; 116:1-5. [DOI: 10.1016/j.enzmictec.2018.05.005] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2018] [Revised: 04/11/2018] [Accepted: 05/10/2018] [Indexed: 01/19/2023]
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11
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The interactions of peripheral membrane proteins with biological membranes. Chem Phys Lipids 2015; 192:51-59. [DOI: 10.1016/j.chemphyslip.2015.07.015] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Revised: 07/14/2015] [Accepted: 07/25/2015] [Indexed: 11/22/2022]
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12
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Kouzuma A, Kasai T, Hirose A, Watanabe K. Catabolic and regulatory systems in Shewanella oneidensis MR-1 involved in electricity generation in microbial fuel cells. Front Microbiol 2015; 6:609. [PMID: 26136738 PMCID: PMC4468914 DOI: 10.3389/fmicb.2015.00609] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2015] [Accepted: 06/02/2015] [Indexed: 12/12/2022] Open
Abstract
Shewanella oneidensis MR-1 is a facultative anaerobe that respires using a variety of inorganic and organic compounds. MR-1 is also capable of utilizing extracellular solid materials, including anodes in microbial fuel cells (MFCs), as electron acceptors, thereby enabling electricity generation. As MFCs have the potential to generate electricity from biomass waste and wastewater, MR-1 has been extensively studied to identify the molecular systems that are involved in electricity generation in MFCs. These studies have demonstrated the importance of extracellular electron-transfer (EET) pathways that electrically connect the quinone pool in the cytoplasmic membrane to extracellular electron acceptors. Electricity generation is also dependent on intracellular catabolic pathways that oxidize electron donors, such as lactate, and regulatory systems that control the expression of genes encoding the components of catabolic and electron-transfer pathways. In addition, recent findings suggest that cell-surface polymers, e.g., exopolysaccharides, and secreted chemicals, which function as electron shuttles, are also involved in electricity generation. Despite these advances in our knowledge on the EET processes in MR-1, further efforts are necessary to fully understand the underlying intra- and extracellular molecular systems for electricity generation in MFCs. We suggest that investigating how MR-1 coordinates these systems to efficiently transfer electrons to electrodes and conserve electrochemical energy for cell proliferation is important for establishing the biological basis for MFCs.
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Affiliation(s)
- Atsushi Kouzuma
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences , Hachioji, Japan
| | - Takuya Kasai
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences , Hachioji, Japan
| | - Atsumi Hirose
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences , Hachioji, Japan
| | - Kazuya Watanabe
- School of Life Sciences, Tokyo University of Pharmacy and Life Sciences , Hachioji, Japan
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13
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Fitzgerald LA, Petersen ER, Leary DH, Nadeau LJ, Soto CM, Ray RI, Little BJ, Ringeisen BR, Johnson GR, Vora GJ, Biffinger JC. Shewanella frigidimarina microbial fuel cells and the influence of divalent cations on current output. Biosens Bioelectron 2013; 40:102-9. [DOI: 10.1016/j.bios.2012.06.039] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2012] [Revised: 06/13/2012] [Accepted: 06/19/2012] [Indexed: 01/04/2023]
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14
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Tomanicek SJ, Johs A, Sawhney MS, Shi L, Liang L. Crystallization and preliminary X-ray crystallographic studies of the outer membrane cytochrome OmcA from Shewanella oneidensis MR-1. Acta Crystallogr Sect F Struct Biol Cryst Commun 2012; 68:53-5. [PMID: 22232171 PMCID: PMC3253834 DOI: 10.1107/s1744309111046082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Accepted: 11/01/2011] [Indexed: 11/11/2022]
Abstract
The outer membrane cytochrome OmcA functions as a terminal metal reductase in the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The ten-heme centers shuttle electrons from the transmembrane donor complex to extracellular electron acceptors. Here, the crystallization and preliminary crystallographic analysis of OmcA are reported. Crystals of OmcA were grown by the sitting-drop vapor-diffusion method using PEG 20,000 as a precipitant. The OmcA crystals belonged to space group P2(1), with unit-cell parameters a = 93.0, b = 246.0, c = 136.6 Å, α = 90, β = 97.8, γ = 90°. X-ray diffraction data were collected to a maximum resolution of 3.25 Å.
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Affiliation(s)
- S J Tomanicek
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
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15
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Xiong Y, Chen B, Shi L, Fredrickson JK, Bigelow DJ, Squier TC. Targeted Protein Degradation of Outer Membrane Decaheme Cytochrome MtrC Metal Reductase in Shewanella oneidensis MR-1 Measured Using Biarsenical Probe CrAsH-EDT2. Biochemistry 2011; 50:9738-51. [DOI: 10.1021/bi200602f] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Yijia Xiong
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Baowei Chen
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Liang Shi
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - James K. Fredrickson
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Diana J. Bigelow
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Thomas C. Squier
- Biological Sciences Division, Fundamental
Sciences
Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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16
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Karlsen OA, Larsen Ø, Jensen HB. The copper responding surfaceome of Methylococccus capsulatus Bath. FEMS Microbiol Lett 2011; 323:97-104. [DOI: 10.1111/j.1574-6968.2011.02365.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Revised: 07/05/2011] [Accepted: 07/11/2011] [Indexed: 11/28/2022] Open
Affiliation(s)
- Odd A. Karlsen
- Department of Molecular Biology; University of Bergen; Norway
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17
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Firer-Sherwood MA, Bewley KD, Mock JY, Elliott SJ. Tools for resolving complexity in the electron transfer networks of multiheme cytochromes c. Metallomics 2011; 3:344-8. [PMID: 21327265 DOI: 10.1039/c0mt00097c] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Examining electron transfer between two proteins with identical spectroscopic signatures is a challenging task. It is supposed that several multiheme cytochromes in Shewanella oneidensis form a molecular "wire" through which electrons are transported across the cellular space and a direct study of this transient protein-protein interaction has not yet been reported. In this study, we present variations on catalytic protein film voltammetry and an anaerobic affinity chromatography assay to demonstrate unidirectional electron transfer between proposed protein pairs. Through use of these techniques, we are able to confirm the transient interactions between these cytochromes, supporting the model of electron transfer that is present in the literature.
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18
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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.
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Johs A, Shi L, Droubay T, Ankner J, Liang L. Characterization of the decaheme c-type cytochrome OmcA in solution and on hematite surfaces by small angle x-ray scattering and neutron reflectometry. Biophys J 2010; 98:3035-43. [PMID: 20550916 PMCID: PMC2884263 DOI: 10.1016/j.bpj.2010.03.049] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2009] [Revised: 03/09/2010] [Accepted: 03/16/2010] [Indexed: 11/25/2022] Open
Abstract
The outer membrane protein OmcA is an 85 kDa decaheme c-type cytochrome located on the surface of the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. It is assumed to mediate shuttling of electrons to extracellular acceptors that include solid metal oxides such as hematite (alpha-Fe(2)O(3)). No information is yet available concerning OmcA structure in physiologically relevant conditions such as aqueous environments. We purified OmcA and characterized its solution structure by small angle x-ray scattering (SAXS), and its interaction at the hematite-water interface by neutron reflectometry. SAXS showed that OmcA is a monomer that adopts a flat ellipsoidal shape with an overall dimension of 34 x 90 x 65 A(3). To our knowledge, we obtained the first direct evidence that OmcA undergoes a redox state-dependent conformational change in solution whereby reduction decreases the overall length of OmcA by approximately 7 A (the maximum dimension was 96 A for oxidized OmcA, and 89 A for NADH and dithionite-reduced OmcA). OmcA was also found to physically interact with electron shuttle molecules such as flavin mononucleotide, resulting in the formation of high-molecular-weight assemblies. Neutron reflectometry showed that OmcA forms a well-defined monomolecular layer on hematite surfaces, where it assumes an orientation that maximizes its contact area with the mineral surface. These novel insights into the molecular structure of OmcA in solution, and its interaction with insoluble hematite and small organic ligands, demonstrate the fundamental structural bases underlying OmcA's role in mediating redox processes.
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Affiliation(s)
- A. Johs
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - L. Shi
- Pacific Northwest National Laboratory, Richland, Washington
| | - T. Droubay
- Pacific Northwest National Laboratory, Richland, Washington
| | - J.F. Ankner
- Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - L. Liang
- Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee
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20
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Tai SK, Wu G, Yuan S, Li KC. Genome-wide expression links the electron transfer pathway of Shewanella oneidensis to chemotaxis. BMC Genomics 2010; 11:319. [PMID: 20492688 PMCID: PMC2886065 DOI: 10.1186/1471-2164-11-319] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Accepted: 05/21/2010] [Indexed: 12/25/2022] Open
Abstract
Background By coupling the oxidation of organic substrates to a broad range of terminal electron acceptors (such as nitrate, metals and radionuclides), Shewanella oneidensis MR-1 has the ability to produce current in microbial fuel cells (MFCs). omcA, mtrA, omcB (also known as mtrC), mtrB, and gspF are some known genes of S. oneidensis MR-1 that participate in the process of electron transfer. How does the cell coordinate the expression of these genes? To shed light on this problem, we obtain the gene expression datasets of MR-1 that are recently public-accessible in Gene Expression Omnibus. We utilize the novel statistical method, liquid association (LA), to investigate the complex pattern of gene regulation. Results Through a web of information obtained by our data analysis, a network of transcriptional regulatory relationship between chemotaxis and electron transfer pathways is revealed, highlighting the important roles of the chemotaxis gene cheA-1, the magnesium transporter gene mgtE-1, and a triheme c-type cytochrome gene SO4572. Conclusion We found previously unknown relationship between chemotaxis and electron transfer using LA system. The study has the potential of helping researchers to overcome the intrinsic metabolic limitation of the microorganisms for improving power density output of an MFC.
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Affiliation(s)
- Shang-Kai Tai
- Institute of Statistical Science, Academia Sinica, Taipei 115, Taiwan
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21
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Bodemer GJ, Antholine WA, Basova LV, Saffarini D, Pacheco AA. The effect of detergents and lipids on the properties of the outer-membrane protein OmcA from Shewanella oneidensis. J Biol Inorg Chem 2010; 15:749-58. [DOI: 10.1007/s00775-010-0643-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2009] [Accepted: 02/24/2010] [Indexed: 11/27/2022]
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22
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Zhao JS, Deng Y, Manno D, Hawari J. Shewanella spp. genomic evolution for a cold marine lifestyle and in-situ explosive biodegradation. PLoS One 2010; 5:e9109. [PMID: 20174598 PMCID: PMC2824531 DOI: 10.1371/journal.pone.0009109] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2009] [Accepted: 01/05/2010] [Indexed: 11/18/2022] Open
Abstract
Shewanella halifaxensis and Shewanella sediminis were among a few aquatic gamma-proteobacteria that were psychrophiles and the first anaerobic bacteria that degraded hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Although many mesophilic or psychrophilic strains of Shewanella and gamma-proteobacteria were sequenced for their genomes, the genomic evolution pathways for temperature adaptation were poorly understood. On the other hand, the genes responsible for anaerobic RDX mineralization pathways remain unknown. To determine the unique genomic properties of bacteria responsible for both cold-adaptation and RDX degradation, the genomes of S. halifaxensis and S. sediminis were sequenced and compared with 108 other gamma-proteobacteria including Shewanella that differ in temperature and Na+ requirements, as well as RDX degradation capability. Results showed that for coping with marine environments their genomes had extensively exchanged with deep sea bacterial genomes. Many genes for Na+-dependent nutrient transporters were recruited to use the high Na+ content as an energy source. For coping with low temperatures, these two strains as well as other psychrophilic strains of Shewanella and gamma-proteobacteria were found to decrease their genome G+C content and proteome alanine, proline and arginine content (p-value <0.01) to increase protein structural flexibility. Compared to poorer RDX-degrading strains, S. halifaxensis and S. sediminis have more number of genes for cytochromes and other enzymes related to RDX metabolic pathways. Experimentally, one cytochrome was found induced in S. halifaxensis by RDX when the chemical was the sole terminal electron acceptor. The isolated protein degraded RDX by mono-denitration and was identified as a multiheme 52 kDa cytochrome using a proteomic approach. The present analyses provided the first insight into divergent genomic evolution of bacterial strains for adaptation to the specific cold marine conditions and to the degradation of the pollutant RDX. The present study also provided the first evidence for the involvement of a specific c-type cytochrome in anaerobic RDX metabolism.
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MESH Headings
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Biodegradation, Environmental
- Chromosome Mapping
- Cold Temperature
- DNA, Bacterial/chemistry
- DNA, Bacterial/genetics
- DNA, Circular/chemistry
- DNA, Circular/genetics
- Evolution, Molecular
- Gammaproteobacteria/classification
- Gammaproteobacteria/genetics
- Genome, Bacterial/genetics
- Genomics
- Marine Biology
- Molecular Structure
- Phylogeny
- Proteomics
- RNA, Ribosomal, 16S/genetics
- Seawater/microbiology
- Sequence Analysis, DNA
- Shewanella/classification
- Shewanella/genetics
- Shewanella/metabolism
- Species Specificity
- Triazines/chemistry
- Triazines/metabolism
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Affiliation(s)
- Jian-Shen Zhao
- Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, Canada
- * E-mail: (JSZ); (JH)
| | - Yinghai Deng
- Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, Canada
| | - Dominic Manno
- Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, Canada
| | - Jalal Hawari
- Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, Canada
- * E-mail: (JSZ); (JH)
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23
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Reardon CL, Dohnalkova AC, Nachimuthu P, Kennedy DW, Saffarini DA, Arey BW, Shi L, Wang Z, Moore D, McLean JS, Moyles D, Marshall MJ, Zachara JM, Fredrickson JK, Beliaev AS. Role of outer-membrane cytochromes MtrC and OmcA in the biomineralization of ferrihydrite by Shewanella oneidensis MR-1. GEOBIOLOGY 2010; 8:56-68. [PMID: 20002197 DOI: 10.1111/j.1472-4669.2009.00226.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In an effort to improve the understanding of electron transfer mechanisms at the microbe-mineral interface, Shewanella oneidensis MR-1 mutants with in-frame deletions of outer-membrane cytochromes (OMCs), MtrC and OmcA, were characterized for the ability to reduce ferrihydrite (FH) using a suite of microscopic, spectroscopic, and biochemical techniques. Analysis of purified recombinant proteins demonstrated that both cytochromes undergo rapid electron exchange with FH in vitro with MtrC displaying faster transfer rates than OmcA. Immunomicroscopy with cytochrome-specific antibodies revealed that MtrC co-localizes with iron solids on the cell surface while OmcA exhibits a more diffuse distribution over the cell surface. After 3-day incubation of MR-1 with FH, pronounced reductive transformation mineral products were visible by electron microscopy. Upon further incubation, the predominant phases identified were ferrous phosphates including vivianite [Fe(3)(PO(4))(2)x8H(2)O] and a switzerite-like phase [Mn(3),Fe(3)(PO(4))(2)x7H(2)O] that were heavily colonized by MR-1 cells with surface-exposed outer-membrane cytochromes. In the absence of both MtrC and OmcA, the cells ability to reduce FH was significantly hindered and no mineral transformation products were detected. Collectively, these results highlight the importance of the outer-membrane cytochromes in the reductive transformation of FH and support a role for direct electron transfer from the OMCs at the cell surface to the mineral.
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Affiliation(s)
- C L Reardon
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA, USA
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24
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The Mtr respiratory pathway is essential for reducing flavins and electrodes in Shewanella oneidensis. J Bacteriol 2009; 192:467-74. [PMID: 19897659 DOI: 10.1128/jb.00925-09] [Citation(s) in RCA: 289] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Mtr respiratory pathway of Shewanella oneidensis strain MR-1 is required to effectively respire both soluble and insoluble forms of oxidized iron. Flavins (riboflavin and flavin mononucleotide) recently have been shown to be excreted by MR-1 and facilitate the reduction of insoluble substrates. Other Shewanella species tested accumulated flavins in supernatants to an extent similar to that of MR-1, suggesting that flavin secretion is a general trait of the species. External flavins have been proposed to act as both a soluble electron shuttle and a metal chelator; however, at biologically relevant concentrations, our results suggest that external flavins primarily act as electron shuttles for MR-1. Using deletion mutants lacking various Mtr-associated proteins, we demonstrate that the Mtr extracellular respiratory pathway is essential for the reduction of flavins and that decaheme cytochromes found on the outer surface of the cell (MtrC and OmcA) are required for the majority of this activity. Given the involvement of external flavins in the reduction of electrodes, we monitored current production by Mtr respiratory pathway mutants in three-electrode bioreactors under controlled flavin concentrations. While mutants lacking MtrC were able to reduce flavins at 50% of the rate of the wild type in cell suspension assays, these strains were unable to grow into productive electrode-reducing biofilms. The analysis of mutants lacking OmcA suggests a role for this protein in both electron transfer to electrodes and attachment to surfaces. The parallel phenotypes of Mtr mutants in flavin and electrode reduction blur the distinction between direct contact and the redox shuttling strategies of insoluble substrate reduction by MR-1.
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25
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Shi L, Richardson DJ, Wang Z, Kerisit SN, Rosso KM, Zachara JM, Fredrickson JK. The roles of outer membrane cytochromes of Shewanella and Geobacter in extracellular electron transfer. ENVIRONMENTAL MICROBIOLOGY REPORTS 2009; 1:220-7. [PMID: 23765850 DOI: 10.1111/j.1758-2229.2009.00035.x] [Citation(s) in RCA: 208] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
As key components of the electron transfer (ET) pathways used for dissimilatory reduction of solid iron [Fe(III)] (hydr)oxides, outer membrane multihaem c-type cytochromes MtrC and OmcA of Shewanella oneidensis MR-1 and OmcE and OmcS of Geobacter sulfurreducens mediate ET reactions extracellularly. Both MtrC and OmcA are at least partially exposed to the extracellular side of the outer membrane and their translocation across the outer membrane is mediated by bacterial type II secretion system. Purified MtrC and OmcA can bind Fe(III) oxides, such as haematite (α-Fe2 O3 ), and directly transfer electrons to the haematite surface. Bindings of MtrC and OmcA to haematite are probably facilitated by their putative haematite-binding motifs whose conserved sequence is Thr-Pro-Ser/Thr. Purified MtrC and OmcA also exhibit broad operating potential ranges that make it thermodynamically feasible to transfer electrons directly not only to Fe(III) oxides but also to other extracellular substrates with different redox potentials. OmcE and OmcS are proposed to be located on the Geobacter cell surface where they are believed to function as intermediates to relay electrons to type IV pili, which are hypothesized to transfer electrons directly to the metal oxides. Cell surface-localized cytochromes thus are key components mediating extracellular ET reactions in both Shewanella and Geobacter for extracellular reduction of Fe(III) oxides.
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Affiliation(s)
- Liang Shi
- Pacific Northwest National Laboratory, Richland, WA 99354, USA. Schools of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
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26
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Kinetic characterization of OmcA and MtrC, terminal reductases involved in respiratory electron transfer for dissimilatory iron reduction in Shewanella oneidensis MR-1. Appl Environ Microbiol 2009; 75:5218-26. [PMID: 19542342 DOI: 10.1128/aem.00544-09] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have used scaling kinetics and the concept of kinetic competence to elucidate the role of hemeproteins OmcA and MtrC in iron reduction by Shewanella oneidensis MR-1. Second-order rate constants for OmcA and MtrC were determined by single-turnover experiments. For soluble iron species, a stopped-flow apparatus was used, and for the less reactive iron oxide goethite, a conventional spectrophotometer was used to measure rates. Steady-state experiments were performed to obtain molecular rate constants by quantifying the OmcA and MtrC contents of membrane fractions and whole cells by Western blot analysis. For reduction of soluble iron, rates determined from transient-state experiments were able to account for rates obtained from steady-state experiments. However, this was not true with goethite; rate constants determined from transient-state experiments were 100 to 1,000 times slower than those calculated from steady-state experiments with membrane fractions and whole cells. In contrast, addition of flavins to the goethite experiments resulted in rates that were consistent with both transient- and steady-state experiments. Kinetic simulations of steady-state results with kinetic constants obtained from transient-state experiments supported flavin involvement. Therefore, we show for the first time that OmcA and MtrC are kinetically competent to account for catalysis of soluble iron reduction in whole Shewanella cells but are not responsible for electron transfer via direct contact alone with insoluble iron-containing minerals. This work supports the hypothesis that electron shuttles are important participants in the reduction of solid Fe phases by this organism.
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27
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Antibody recognition force microscopy shows that outer membrane cytochromes OmcA and MtrC are expressed on the exterior surface of Shewanella oneidensis MR-1. Appl Environ Microbiol 2009; 75:2931-5. [PMID: 19286784 DOI: 10.1128/aem.02108-08] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Antibody recognition force microscopy showed that OmcA and MtrC are expressed on the exterior surface of living Shewanella oneidensis MR-1 cells when Fe(III), including solid-phase hematite (Fe(2)O(3)), was the terminal electron acceptor. OmcA was localized to the interface between the cell and mineral. MtrC displayed a more uniform distribution across the cell surface. Both cytochromes were associated with an extracellular polymeric substance.
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28
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Mechanism and Consequences of anaerobic respiration of cobalt by Shewanella oneidensis strain MR-1. Appl Environ Microbiol 2008; 74:6880-6. [PMID: 18836009 DOI: 10.1128/aem.00840-08] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacteria from the genus Shewanella are the most diverse respiratory organisms studied to date and can utilize a variety of metals and metal(loid)s as terminal electron acceptors. These bacteria can potentially be used in bioremediation applications since the redox state of metals often influences both solubility and toxicity. Understanding molecular mechanisms by which metal transformations occur and the consequences of by-products that may be toxic to the organism and thus inhibitory to the overall process is significant to future applications for bioremediation. Here, we examine the ability of Shewanella oneidensis to catalyze the reduction of chelated cobalt. We describe an unexpected ramification of [Co(III)-EDTA](-) reduction by S. oneidensis: the formation of a toxic by-product. We found that [Co(II)-EDTA](2-), the product of [Co(III)-EDTA](-) respiration, inhibited the growth of S. oneidensis strain MR-1 and that this toxicity was partially abolished by the addition of MgSO(4). We demonstrate that [Co(III)-EDTA](-) reduction by S. oneidensis requires the Mtr extracellular respiratory pathway and associated pathways required to develop functional Mtr enzymes (the c-type cytochrome maturation pathway) and ensure proper localization (type II secretion). The Mtr pathway is known to be required for a variety of substrates, including some chelated and insoluble metals and organic compounds. Understanding the full substrate range for the Mtr pathway is crucial for developing S. oneidensis strains as a tool for bioremediation.
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29
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Karlsen OA, Lillehaug JR, Jensen HB. The presence of multiple c-type cytochromes at the surface of the methanotrophic bacterium Methylococcus capsulatus (Bath) is regulated by copper. Mol Microbiol 2008; 70:15-26. [PMID: 18681943 DOI: 10.1111/j.1365-2958.2008.06380.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Identification of surface proteins is essential to understand bacterial communication with its environment. Analysis of the surface-associated proteins of Methylococcus capsulatus (Bath) revealed a highly dynamic structure responding closely to the availability of copper in the medium in the range from approximately 0 to 10 microM. Several c-type cytochromes, including three novel multihaem proteins, are present at the cellular surface, a feature that is otherwise a peculiarity of dissimilatory metal-reducing bacteria. At low copper concentrations, the cytochrome c(553o) and the cytochrome c(553o) family protein, encoded by the MCA0421 and MCA0423 genes, respectively, are major constituents of the surfaceome and show a fine-tuned copper-dependent regulation of expression. Two novel members of the cytochrome c(553o) family were identified: MCA0338 was abundant between 5 and 10 microM copper, while MCA2259 was detected only in the surface fraction obtained from approximately 0 microM copper cultures. The presence at the bacterial surface of several c-type cytochromes, generally involved in energy transduction, indicates strongly that redox processes take place at the bacterial surface. Due to the unique role of copper in the biology of M. capsulatus (Bath), it appears that c-type cytochromes have essential functions in copper homeostasis allowing the cells to adapt to varying copper exposure.
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Affiliation(s)
- O A Karlsen
- Department of Molecular Biology, University of Bergen, Bergen, Norway.
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30
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Fredrickson JK, Romine MF, Beliaev AS, Auchtung JM, Driscoll ME, Gardner TS, Nealson KH, Osterman AL, Pinchuk G, Reed JL, Rodionov DA, Rodrigues JLM, Saffarini DA, Serres MH, Spormann AM, Zhulin IB, Tiedje JM. Towards environmental systems biology of Shewanella. Nat Rev Microbiol 2008; 6:592-603. [PMID: 18604222 DOI: 10.1038/nrmicro1947] [Citation(s) in RCA: 629] [Impact Index Per Article: 39.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Bacteria of the genus Shewanella are known for their versatile electron-accepting capacities, which allow them to couple the decomposition of organic matter to the reduction of the various terminal electron acceptors that they encounter in their stratified environments. Owing to their diverse metabolic capabilities, shewanellae are important for carbon cycling and have considerable potential for the remediation of contaminated environments and use in microbial fuel cells. Systems-level analysis of the model species Shewanella oneidensis MR-1 and other members of this genus has provided new insights into the signal-transduction proteins, regulators, and metabolic and respiratory subsystems that govern the remarkable versatility of the shewanellae.
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Affiliation(s)
- James K Fredrickson
- Biological Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA. ;
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31
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Electrochemical interrogations of the Mtr cytochromes from Shewanella: opening a potential window. J Biol Inorg Chem 2008; 13:849-54. [DOI: 10.1007/s00775-008-0398-z] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2008] [Accepted: 06/12/2008] [Indexed: 10/21/2022]
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32
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Direct involvement of type II secretion system in extracellular translocation of Shewanella oneidensis outer membrane cytochromes MtrC and OmcA. J Bacteriol 2008; 190:5512-6. [PMID: 18502849 DOI: 10.1128/jb.00514-08] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
MtrC and OmcA are cell surface-exposed lipoproteins important for reducing solid metal oxides. Deletions of type II secretion system (T2SS) genes reduced their extracellular release and their accessibility to the proteinase K treatment, demonstrating the direct involvement of T2SS in translocation of MtrC and OmcA to the bacterial cell surface.
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33
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The c-type cytochrome OmcA localizes to the outer membrane upon heterologous expression in Escherichia coli. J Bacteriol 2008; 190:5127-31. [PMID: 18487320 DOI: 10.1128/jb.00395-08] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have functionally produced the outer membrane cytochrome OmcA from Shewanella oneidensis in Escherichia coli. Substrate accessibility experiments indicate that OmcA is surface exposed in an E. coli B strain but not in a K-12 strain. We show that a functional type II secretion system is required for surface localization.
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34
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Lower BH, Lins RD, Oestreicher Z, Straatsma TP, Hochella MF, Shi L, Lower SK. In vitro evolution of a peptide with a hematite binding motif that may constitute a natural metal-oxide binding archetype. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2008; 42:3821-3827. [PMID: 18546729 DOI: 10.1021/es702688c] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Phage-display technology was used to evolve peptides that selectively bind to the metal-oxide hematite (Fe2O3) from a library of approximately 3 billion different polypeptides. The sequences of these peptides contained the highly conserved amino acid motif, Ser/Thr-hydrophobic/aromatic-Ser/Thr-Pro-Ser/Thr. To better understand the nature of the peptide-metal oxide binding demonstrated by these experiments, molecular dynamics simulations were carried out for Ser-Pro-Ser at a hematite surface. These simulations show that hydrogen bonding occurs between the two serine amino acids and the hydroxylated hematite surface and that the presence of proline between the hydroxide residues restricts the peptide flexibility, thereby inducing a structural-binding motif. A search of published sequence data revealed that the binding motif (Ser/Thr-Pro-Ser/Thr) is adjacent to the terminal heme-binding domain of both OmcA and MtrC, which are outer membrane cytochromes from the metal-reducing bacterium Shewanella oneidensis MR-1. The entire five amino acid consensus sequence (Ser/Thr-hydrophobic/ aromatic-Ser/Thr-Pro-Ser/Thr) was also found as multiple copies in the primary sequences of metal-oxide binding proteins Sil1 and Sil2 from Thalassiosira pseudonana. We suggest that this motif constitutes a natural metal-oxide binding archetype that could be exploited in enzyme-based biofuel cell design and approaches to synthesize tailored metal-oxide nanostructures.
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Affiliation(s)
- Brian H Lower
- Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
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35
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Korenevsky A, Beveridge TJ. The surface physicochemistry and adhesiveness of Shewanella are affected by their surface polysaccharides. MICROBIOLOGY-SGM 2007; 153:1872-1883. [PMID: 17526844 DOI: 10.1099/mic.0.2006/003814-0] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Shewanella strains have previously been studied with regard to their cell surface ultrastructure and LPS composition. They have now been further characterized with respect to their surface physicochemistry and ability to adhere to haematite. The surfaces of the Shewanella strains were found to be electronegative and hydrophilic, and these properties could be correlated with LPS composition or the presence of capsular polysaccharides. Strains expressing rough LPS with no capsule were more hydrophobic and electronegative than those possessing smooth LPS or capsules. By combining different approaches, such as contact-angle measurement, hydrophilic/hydrophobic chromatography, microelectrophoresis, adhesion assays and calculation of interaction energies, it was shown that electrostatic interactions predominate over hydrophobic interactions at the cell-iron oxide interface. Bacterial adhesion to haematite was significantly reduced in strains expressing smooth LPS or a capsule. These findings remained true for Shewanella strains grown under either aerobic or anaerobic conditions, although the surfaces of anaerobic cells appeared to be less electronegative and more hydrophilic than those of aerobic cells.
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Affiliation(s)
- Anton Korenevsky
- Department of Molecular and Cellular Biology and Advanced Foods and Materials Network - Networks of Centres of Excellence, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Terry J Beveridge
- Department of Molecular and Cellular Biology and Advanced Foods and Materials Network - Networks of Centres of Excellence, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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Shi L, Squier TC, Zachara JM, Fredrickson JK. Respiration of metal (hydr)oxides by Shewanella and Geobacter: a key role for multihaem c-type cytochromes. Mol Microbiol 2007; 65:12-20. [PMID: 17581116 PMCID: PMC1974784 DOI: 10.1111/j.1365-2958.2007.05783.x] [Citation(s) in RCA: 425] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Dissimilatory reduction of metal (e.g. Fe, Mn) (hydr)oxides represents a challenge for microorganisms, as their cell envelopes are impermeable to metal (hydr)oxides that are poorly soluble in water. To overcome this physical barrier, the Gram-negative bacteria Shewanella oneidensis MR-1 and Geobacter sulfurreducens have developed electron transfer (ET) strategies that require multihaem c-type cytochromes (c-Cyts). In S. oneidensis MR-1, multihaem c-Cyts CymA and MtrA are believed to transfer electrons from the inner membrane quinone/quinol pool through the periplasm to the outer membrane. The type II secretion system of S. oneidensis MR-1 has been implicated in the reduction of metal (hydr)oxides, most likely by translocating decahaem c-Cyts MtrC and OmcA across outer membrane to the surface of bacterial cells where they form a protein complex. The extracellular MtrC and OmcA can directly reduce solid metal (hydr)oxides. Likewise, outer membrane multihaem c-Cyts OmcE and OmcS of G. sulfurreducens are suggested to transfer electrons from outer membrane to type IV pili that are hypothesized to relay the electrons to solid metal (hydr)oxides. Thus, multihaem c-Cyts play critical roles in S. oneidensis MR-1- and G. sulfurreducens-mediated dissimilatory reduction of solid metal (hydr)oxides by facilitating ET across the bacterial cell envelope.
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Affiliation(s)
- Liang Shi
- For corresspondence. *E-mail ; Tel. (+1) 509 376 4834; Fax (+1) 509 372 1632
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Hartshorne RS, Jepson BN, Clarke TA, Field SJ, Fredrickson J, Zachara J, Shi L, Butt JN, Richardson DJ. Characterization of Shewanella oneidensis MtrC: a cell-surface decaheme cytochrome involved in respiratory electron transport to extracellular electron acceptors. J Biol Inorg Chem 2007; 12:1083-94. [PMID: 17701062 DOI: 10.1007/s00775-007-0278-y] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2007] [Accepted: 07/09/2007] [Indexed: 10/23/2022]
Abstract
MtrC is a decaheme c-type cytochrome associated with the outer cell membrane of Fe(III)-respiring species of the Shewanella genus. It is proposed to play a role in anaerobic respiration by mediating electron transfer to extracellular mineral oxides that can serve as terminal electron acceptors. The present work presents the first spectropotentiometric and voltammetric characterization of MtrC, using protein purified from Shewanella oneidensis MR-1. Potentiometric titrations, monitored by UV-vis absorption and electron paramagnetic resonance (EPR) spectroscopy, reveal that the hemes within MtrC titrate over a broad potential range spanning between approximately +100 and approximately -500 mV (vs. the standard hydrogen electrode). Across this potential window the UV-vis absorption spectra are characteristic of low-spin c-type hemes and the EPR spectra reveal broad, complex features that suggest the presence of magnetically spin-coupled low-spin c-hemes. Non-catalytic protein film voltammetry of MtrC demonstrates reversible electrochemistry over a potential window similar to that disclosed spectroscopically. The voltammetry also allows definition of kinetic properties of MtrC in direct electron exchange with a solid electrode surface and during reduction of a model Fe(III) substrate. Taken together, the data provide quantitative information on the potential domain in which MtrC can operate.
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Affiliation(s)
- Robert S Hartshorne
- Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
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Bretschger O, Obraztsova A, Sturm CA, Chang IS, Gorby YA, Reed SB, Culley DE, Reardon CL, Barua S, Romine MF, Zhou J, Beliaev AS, Bouhenni R, Saffarini D, Mansfeld F, Kim BH, Fredrickson JK, Nealson KH. Current production and metal oxide reduction by Shewanella oneidensis MR-1 wild type and mutants. Appl Environ Microbiol 2007; 73:7003-12. [PMID: 17644630 PMCID: PMC2074945 DOI: 10.1128/aem.01087-07] [Citation(s) in RCA: 361] [Impact Index Per Article: 21.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Shewanella oneidensis MR-1 is a gram-negative facultative anaerobe capable of utilizing a broad range of electron acceptors, including several solid substrates. S. oneidensis MR-1 can reduce Mn(IV) and Fe(III) oxides and can produce current in microbial fuel cells. The mechanisms that are employed by S. oneidensis MR-1 to execute these processes have not yet been fully elucidated. Several different S. oneidensis MR-1 deletion mutants were generated and tested for current production and metal oxide reduction. The results showed that a few key cytochromes play a role in all of the processes but that their degrees of participation in each process are very different. Overall, these data suggest a very complex picture of electron transfer to solid and soluble substrates by S. oneidensis MR-1.
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Affiliation(s)
- Orianna Bretschger
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, USA
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Borloo J, Vergauwen B, De Smet L, Brigé A, Motte B, Devreese B, Van Beeumen J. A kinetic approach to the dependence of dissimilatory metal reduction by Shewanella oneidensis MR-1 on the outer membrane cytochromes c OmcA and OmcB. FEBS J 2007; 274:3728-3738. [PMID: 17608722 DOI: 10.1111/j.1742-4658.2007.05907.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The Gram-negative bacterium Shewanella oneidensis MR-1 shows a remarkably versatile anaerobic respiratory metabolism. One of its hallmarks is its ability to grow and survive through the reduction of metallic compounds. Among other proteins, outer membrane decaheme cytochromes c OmcA and OmcB have been identified as key players in metal reduction. In fact, both of these cytochromes have been proposed to be terminal Fe(III) and Mn(IV) reductases, although their role in the reduction of other metals is less well understood. To obtain more insight into this, we constructed and analyzed omcA, omcB and omcA/omcB insertion mutants of S. oneidensis MR-1. Anaerobic growth on Fe(III), V(V), Se(VI) and U(VI) revealed a requirement for both OmcA and OmcB in Fe(III) reduction, a redundant function in V(V) reduction, and no apparent involvement in Se(VI) and U(VI) reduction. Growth of the omcB(-) mutant on Fe(III) was more affected than growth of the omcA(-) mutant, suggesting OmcB to be the principal Fe(III) reductase. This result was corroborated through the examination of whole cell kinetics of OmcA- and OmcB-dependent Fe(III)-nitrilotriacetic acid reduction, showing that OmcB is approximately 11.5 and approximately 6.3 times faster than OmcA at saturating and low nonsaturating concentrations of Fe(III)-nitrilotriacetic acid, respectively, whereas the omcA(-) omcB(-) double mutant was devoid of Fe(III)-nitrilotriacetic acid reduction activity. These experiments reveal, for the first time, that OmcA and OmcB are the sole terminal Fe(III) reductases present in S. oneidensis MR-1. Kinetic inhibition experiments further revealed vanadate (V(2)O(5)) to be a competitive and mixed-type inhibitor of OmcA and OmcB, respectively, showing similar affinities relative to Fe(III)-nitrilotriacetic acid. Neither sodium selenate nor uranyl acetate were found to inhibit OmcA- and OmcB-dependent Fe(III)-nitrilotriacetic acid reduction. Taken together with our growth experiments, this suggests that proteins other than OmcA and OmcB play key roles in anaerobic Se(VI) and U(VI) respiration.
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Affiliation(s)
- Jimmy Borloo
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Bjorn Vergauwen
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Lina De Smet
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Ann Brigé
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Bart Motte
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Bart Devreese
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
| | - Jozef Van Beeumen
- Laboratory for Protein Biochemistry and Protein Engineering, Ghent University, Belgium
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Jiao Y, Newman DK. The pio operon is essential for phototrophic Fe(II) oxidation in Rhodopseudomonas palustris TIE-1. J Bacteriol 2007; 189:1765-73. [PMID: 17189359 PMCID: PMC1855732 DOI: 10.1128/jb.00776-06] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2006] [Accepted: 12/12/2006] [Indexed: 11/20/2022] Open
Abstract
Phototrophic Fe(II)-oxidizing bacteria couple the oxidation of ferrous iron [Fe(II)] to reductive CO(2) fixation by using light energy, but until recently, little has been understood about the molecular basis for this process. Here we report the discovery, with Rhodopseudomonas palustris TIE-1 as a model organism, of a three-gene operon, designated the pio operon (for phototrophic iron oxidation), that is necessary for phototrophic Fe(II) oxidation. The first gene in the operon, pioA, encodes a c-type cytochrome that is upregulated under Fe(II)-grown conditions. PioA contains a signal sequence and shares homology with MtrA, a decaheme c-type cytochrome from Shewanella oneidensis MR-1. The second gene, pioB, encodes a putative outer membrane beta-barrel protein. PioB is a homologue of MtrB from S. oneidensis MR-1. The third gene, pioC, encodes a putative high potential iron sulfur protein (HiPIP) with a twin-arginine translocation (Tat) signal sequence and is similar to the putative Fe(II) oxidoreductase (Iro) from Acidithiobacillus ferrooxidans. Like PioA, PioB and PioC appear to be secreted proteins. Deletion of the pio operon results in loss of Fe(II) oxidation activity and growth on Fe(II). Complementation studies confirm that the phenotype of this mutant is due to loss of the pio genes. Deletion of pioA alone results in loss of almost all Fe(II) oxidation activity; however, deletion of either pioB or pioC alone results in only partial loss of Fe(II) oxidation activity. Together, these results suggest that proteins encoded by the pio operon are essential and specific for phototrophic Fe(II) oxidation in R. palustris TIE-1.
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Affiliation(s)
- Yongqin Jiao
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
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Croal LR, Jiao Y, Newman DK. The fox operon from Rhodobacter strain SW2 promotes phototrophic Fe(II) oxidation in Rhodobacter capsulatus SB1003. J Bacteriol 2006; 189:1774-82. [PMID: 17189371 PMCID: PMC1855712 DOI: 10.1128/jb.01395-06] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Anoxygenic photosynthesis based on Fe(II) is thought to be one of the most ancient forms of metabolism and is hypothesized to represent a transition step in the evolution of oxygenic photosynthesis. However, little is known about the molecular basis of this process because, until recently (Y. Jiao and D. K. Newman, J. Bacteriol. 189:1765-1773, 2007), most phototrophic Fe(II)-oxidizing bacteria have been genetically intractable. In this study, we circumvented this problem by taking a heterologous-complementation approach to identify a three-gene operon (the foxEYZ operon) from Rhodobacter sp. strain SW2 that confers enhanced light-dependent Fe(II) oxidation activity when expressed in its genetically tractable relative Rhodobacter capsulatus SB1003. The first gene in this operon, foxE, encodes a c-type cytochrome with no significant similarity to other known proteins. Expression of foxE alone confers significant light-dependent Fe(II) oxidation activity on SB1003, but maximal activity is achieved when foxE is expressed with the two downstream genes foxY and foxZ. In SW2, the foxE and foxY genes are cotranscribed in the presence of Fe(II) and/or hydrogen, with foxZ being transcribed only in the presence of Fe(II). Sequence analysis predicts that foxY encodes a protein containing the redox cofactor pyrroloquinoline quinone and that foxZ encodes a protein with a transport function. Future biochemical studies will permit the localization and function of the Fox proteins in SW2 to be determined.
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Affiliation(s)
- Laura R Croal
- California Institute of Technology, Pasadena, CA 91125, USA
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Gralnick JA, Vali H, Lies DP, Newman DK. Extracellular respiration of dimethyl sulfoxide by Shewanella oneidensis strain MR-1. Proc Natl Acad Sci U S A 2006; 103:4669-74. [PMID: 16537430 PMCID: PMC1450229 DOI: 10.1073/pnas.0505959103] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Shewanella species are renowned for their respiratory versatility, including their ability to respire poorly soluble substrates by using enzymatic machinery that is localized to the outside of the cell. The ability to engage in "extracellular respiration" to date has focused primarily on respiration of minerals. Here, we identify two gene clusters in Shewanella oneidensis strain MR-1 that each contain homologs of genes required for metal reduction and genes that are predicted to encode dimethyl sulfoxide (DMSO) reductase subunits. Molecular and genetic analyses of these clusters indicate that one (SO1427-SO1432) is required for anaerobic respiration of DMSO. We show that DMSO respiration is an extracellular respiratory process through the analysis of mutants defective in type II secretion, which is required for transporting proteins to the outer membrane in Shewanella. Moreover, immunogold labeling of DMSO reductase subunits reveals that they reside on the outer leaflet of the outer membrane under anaerobic conditions. The extracellular localization of the DMSO reductase in S. oneidensis suggests these organisms may perceive DMSO in the environment as an insoluble compound.
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Affiliation(s)
- Jeffrey A Gralnick
- Divisions of Geological and Planetary Sciences and Biology, and Howard Hughes Medical Institute, California Institute of Technology, Pasadena, CA 91125, USA.
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