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Zhang J, Li F, Liu D, Liu Q, Song H. Engineering extracellular electron transfer pathways of electroactive microorganisms by synthetic biology for energy and chemicals production. Chem Soc Rev 2024; 53:1375-1446. [PMID: 38117181 DOI: 10.1039/d3cs00537b] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2023]
Abstract
The excessive consumption of fossil fuels causes massive emission of CO2, leading to climate deterioration and environmental pollution. The development of substitutes and sustainable energy sources to replace fossil fuels has become a worldwide priority. Bio-electrochemical systems (BESs), employing redox reactions of electroactive microorganisms (EAMs) on electrodes to achieve a meritorious combination of biocatalysis and electrocatalysis, provide a green and sustainable alternative approach for bioremediation, CO2 fixation, and energy and chemicals production. EAMs, including exoelectrogens and electrotrophs, perform extracellular electron transfer (EET) (i.e., outward and inward EET), respectively, to exchange energy with the environment, whose rate determines the efficiency and performance of BESs. Therefore, we review the synthetic biology strategies developed in the last decade for engineering EAMs to enhance the EET rate in cell-electrode interfaces for facilitating the production of electricity energy and value-added chemicals, which include (1) progress in genetic manipulation and editing tools to achieve the efficient regulation of gene expression, knockout, and knockdown of EAMs; (2) synthetic biological engineering strategies to enhance the outward EET of exoelectrogens to anodes for electricity power production and anodic electro-fermentation (AEF) for chemicals production, including (i) broadening and strengthening substrate utilization, (ii) increasing the intracellular releasable reducing equivalents, (iii) optimizing c-type cytochrome (c-Cyts) expression and maturation, (iv) enhancing conductive nanowire biosynthesis and modification, (v) promoting electron shuttle biosynthesis, secretion, and immobilization, (vi) engineering global regulators to promote EET rate, (vii) facilitating biofilm formation, and (viii) constructing cell-material hybrids; (3) the mechanisms of inward EET, CO2 fixation pathway, and engineering strategies for improving the inward EET of electrotrophic cells for CO2 reduction and chemical production, including (i) programming metabolic pathways of electrotrophs, (ii) rewiring bioelectrical circuits for enhancing inward EET, and (iii) constructing microbial (photo)electrosynthesis by cell-material hybridization; (4) perspectives on future challenges and opportunities for engineering EET to develop highly efficient BESs for sustainable energy and chemical production. We expect that this review will provide a theoretical basis for the future development of BESs in energy harvesting, CO2 fixation, and chemical synthesis.
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Affiliation(s)
- Junqi Zhang
- Frontier Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, and School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
| | - Feng Li
- Frontier Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, and School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
| | - Dingyuan Liu
- Frontier Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, and School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
| | - Qijing Liu
- Frontier Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, and School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
| | - Hao Song
- Frontier Science Center for Synthetic Biology (Ministry of Education), Key Laboratory of Systems Bioengineering, and School of Chemical Engineering and Technology, Tianjin University, Tianjin, 300072, China.
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2
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Xiang Y, Guo Y, Liu G, Liu Y, Song M, Shi J, Hu L, Yin Y, Cai Y, Jiang G. Direct Uptake and Intracellular Dissolution of HgS Nanoparticles: Evidence from a Bacterial Biosensor Approach. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:14994-15003. [PMID: 37755700 DOI: 10.1021/acs.est.3c02664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/28/2023]
Abstract
Mercury sulfide nanoparticles (HgSNPs), which occur widely in oxic and anoxic environments, can be microbially converted to highly toxic methylmercury or volatile elemental mercury, but it remains challenging to assess their bioavailability. In this study, an Escherichia coli-based whole-cell fluorescent biosensor was developed to explore the bioavailability and microbial activation process of HgSNPs. Results show that HgSNPs (3.17 ± 0.96 nm) trigger a sharp increase in fluorescence intensity of the biosensor, with signal responses almost equal to that of ionic Hg (Hg(II)) within 10 h, indicating high bioavailability of HgSNP. The intracellular total Hg (THg) of cells exposed to HgSNPs (200 μg L-1) was 3.52-8.59-folds higher than that of cells exposed to Hg(II) (200 μg L-1), suggesting that intracellular HgSNPs were only partially dissolved. Speciation analysis using size-exclusion chromatography (SEC)-inductively coupled plasma mass spectrometry (ICP-MS) revealed that the bacterial filtrate was not responsible for HgSNP dissolution, suggesting that HgSNPs entered cells in nanoparticle form. Combined with fluorescence intensity and intracellular THg analysis, the intracellular HgSNP dissolution ratio was estimated at 22-29%. Overall, our findings highlight the rapid internalization and high intracellular dissolution ratio of HgSNPs by E. coli, and intracellular THg combined with biosensors could provide innovative tools to explore the microbial uptake and dissolution of HgSNPs.
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Affiliation(s)
- Yuping Xiang
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yingying Guo
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Guangliang Liu
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Yanwei Liu
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Maoyong Song
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jianbo Shi
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Ligang Hu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Yongguang Yin
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Institute of Environment and Health, Jianghan University, Wuhan 430056, China
| | - Yong Cai
- Laboratory of Environmental Nanotechnology and Health Effect, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Guibin Jiang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
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Liu JQ, Min D, He RL, Cheng ZH, Wu J, Liu DF. Efficient and precise control of gene expression in Geobacter sulfurreducens through new genetic elements and tools for pollutant conversion. Biotechnol Bioeng 2023; 120:3001-3012. [PMID: 37209207 DOI: 10.1002/bit.28433] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Revised: 05/05/2023] [Accepted: 05/07/2023] [Indexed: 05/22/2023]
Abstract
Geobacter species, exhibiting exceptional extracellular electron transfer aptitude, hold great potential for applications in pollution remediation, bioenergy production, and natural elemental cycles. Nonetheless, a scarcity of well-characterized genetic elements and gene expression tools constrains the effective and precise fine-tuning of gene expression in Geobacter species, thereby limiting their applications. Here, we examined a suite of genetic elements and developed a new genetic editing tool in Geobacter sulfurreducens to enhance their pollutant conversion capacity. First, the performances of the widely used inducible promoters, constitutive promoters, and ribosomal binding sites (RBSs) elements in G. sulfurreducens were quantitatively evaluated. Also, six native promoters with superior expression levels than constitutive promoters were identified on the genome of G. sulfurreducens. Employing the characterized genetic elements, the clustered regularly interspaced short palindromic repeats interference (CRISPRi) system was constructed in G. sulfurreducens to achieve the repression of an essential gene-aroK and morphogenic genes-ftsZ and mreB. Finally, applying the engineered strain to the reduction of tungsten trioxide (WO3 ), methyl orange (MO), and Cr(VI), We found that morphological elongation through ftsZ repression amplified the extracellular electron transfer proficiency of G. sulfurreducens and facilitated its contaminant transformation efficiency. These new systems provide rapid, versatile, and scalable tools poised to expedite advancements in Geobacter genomic engineering to favor environmental and other biotechnological applications.
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Affiliation(s)
- Jia-Qi Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei, China
| | - Di Min
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei, China
| | - Ru-Li He
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei, China
| | - Zhou-Hua Cheng
- School of Life Sciences, University of Science & Technology of China, Hefei, China
| | - Jie Wu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei, China
| | - Dong-Feng Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei, China
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Lloyd CJ, Guo S, Kinrade B, Zahiri H, Eves R, Ali SK, Yildiz F, Voets IK, Davies PL, Klose KE. A peptide-binding domain shared with an Antarctic bacterium facilitates Vibrio cholerae human cell binding and intestinal colonization. Proc Natl Acad Sci U S A 2023; 120:e2308238120. [PMID: 37729203 PMCID: PMC10523503 DOI: 10.1073/pnas.2308238120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2023] [Accepted: 07/31/2023] [Indexed: 09/22/2023] Open
Abstract
Vibrio cholerae, the causative agent of the disease cholera, is responsible for multiple pandemics. V. cholerae binds to and colonizes the gastrointestinal tract within the human host, as well as various surfaces in the marine environment (e.g., zooplankton) during interepidemic periods. A large adhesin, the Flagellar Regulated Hemagglutinin A (FrhA), enhances binding to erythrocytes and epithelial cells and enhances intestinal colonization. We identified a peptide-binding domain (PBD) within FrhA that mediates hemagglutination, binding to epithelial cells, intestinal colonization, and facilitates biofilm formation. Intriguingly, this domain is also found in the ice-binding protein of the Antarctic bacterium Marinomonas primoryensis, where it mediates binding to diatoms. Peptide inhibitors of the M. primoryensis PBD inhibit V. cholerae binding to human cells as well as to diatoms and inhibit biofilm formation. Moreover, the M. primoryensis PBD inserted into FrhA allows V. cholerae to bind human cells and colonize the intestine and also enhances biofilm formation, demonstrating the interchangeability of the PBD from these bacteria. Importantly, peptide inhibitors of PBD reduce V. cholerae intestinal colonization in infant mice. These studies demonstrate how V. cholerae uses a PBD shared with a diatom-binding Antarctic bacterium to facilitate intestinal colonization in humans and biofilm formation in the environment.
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Affiliation(s)
- Cameron J. Lloyd
- South Texas Center for Emerging Infectious Diseases, University of Texas, San Antonio, TX78249
- Department of Molecular Microbiology and Immunology, University of Texas, San Antonio, TX78249
| | - Shuaiqi Guo
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ONK7L 3N6, Canada
| | - Brett Kinrade
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ONK7L 3N6, Canada
| | - Hossein Zahiri
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ONK7L 3N6, Canada
| | - Robert Eves
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ONK7L 3N6, Canada
| | - Syed Khalid Ali
- South Texas Center for Emerging Infectious Diseases, University of Texas, San Antonio, TX78249
- Department of Molecular Microbiology and Immunology, University of Texas, San Antonio, TX78249
| | - Fitnat Yildiz
- Department of Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA95064
| | - Ilja K. Voets
- Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, Eindhoven5612, the Netherlands
| | - Peter L. Davies
- Department of Biomedical and Molecular Sciences, Queen’s University, Kingston, ONK7L 3N6, Canada
| | - Karl E. Klose
- South Texas Center for Emerging Infectious Diseases, University of Texas, San Antonio, TX78249
- Department of Molecular Microbiology and Immunology, University of Texas, San Antonio, TX78249
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5
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Fessler M, Madsen JS, Zhang Y. Conjugative plasmids inhibit extracellular electron transfer in Geobacter sulfurreducens. Front Microbiol 2023; 14:1150091. [PMID: 37007462 PMCID: PMC10063792 DOI: 10.3389/fmicb.2023.1150091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 02/20/2023] [Indexed: 03/19/2023] Open
Abstract
Geobacter sulfurreducens is part of a specialized group of microbes with the unique ability to exchange electrons with insoluble materials, such as iron oxides and electrodes. Therefore, G. sulfurreducens plays an essential role in the biogeochemical iron cycle and microbial electrochemical systems. In G. sulfurreducens this ability is primarily dependent on electrically conductive nanowires that link internal electron flow from metabolism to solid electron acceptors in the extracellular environment. Here we show that when carrying conjugative plasmids, which are self-transmissible plasmids that are ubiquitous in environmental bacteria, G. sulfurreducens reduces insoluble iron oxides at much slower rates. This was the case for all three conjugative plasmids tested (pKJK5, RP4 and pB10). Growth with electron acceptors that do not require expression of nanowires was, on the other hand, unaffected. Furthermore, iron oxide reduction was also inhibited in Geobacter chapellei, but not in Shewanella oneidensis where electron export is nanowire-independent. As determined by transcriptomics, presence of pKJK5 reduces transcription of several genes that have been shown to be implicated in extracellular electron transfer in G. sulfurreducens, including pilA and omcE. These results suggest that conjugative plasmids can in fact be very disadvantageous for the bacterial host by imposing specific phenotypic changes, and that these plasmids may contribute to shaping the microbial composition in electrode-respiring biofilms in microbial electrochemical reactors.
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Affiliation(s)
- Mathias Fessler
- Department of Environmental and Resource Engineering, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Jonas Stenløkke Madsen
- Section of Microbiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Yifeng Zhang
- Department of Environmental and Resource Engineering, Technical University of Denmark, Kongens Lyngby, Denmark
- *Correspondence: Yifeng Zhang,
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6
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Joshi K, Chan CH, Levar CE, Bond DR. Single Amino Acid Residues Control Potential‐Dependent Inactivation of an Inner Membrane
bc‐
Cytochrome**. ChemElectroChem 2022. [DOI: 10.1002/celc.202200907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Komal Joshi
- Department of Biochemistry Molecular Biology and Biophysics University of Minnesota Twin Cities St. Paul MN 55108 USA
- The BioTechnology Institute University of Minnesota Twin Cities St. Paul MN 55108 USA
| | - Chi H. Chan
- The BioTechnology Institute University of Minnesota Twin Cities St. Paul MN 55108 USA
| | - Caleb E. Levar
- The BioTechnology Institute University of Minnesota Twin Cities St. Paul MN 55108 USA
| | - Daniel R. Bond
- The BioTechnology Institute University of Minnesota Twin Cities St. Paul MN 55108 USA
- Department of Plant and Microbial Biology University of Minnesota Twin Cities St. Paul MN 55108 USA
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7
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Choi S, Chan CH, Bond DR. Lack of Specificity in Geobacter Periplasmic Electron Transfer. J Bacteriol 2022; 204:e0032222. [PMID: 36383007 PMCID: PMC9765071 DOI: 10.1128/jb.00322-22] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Accepted: 10/23/2022] [Indexed: 11/17/2022] Open
Abstract
Reduction of extracellular acceptors requires electron transfer across the periplasm. In Geobacter sulfurreducens, three separate cytoplasmic membrane cytochromes are utilized depending on redox potential, and at least five cytochrome conduits span the outer membrane. Because G. sulfurreducens produces 5 structurally similar triheme periplasmic cytochromes (PpcABCDE) that differ in expression level, midpoint potential, and heme biochemistry, many hypotheses propose distinct periplasmic carriers could be used for specific redox potentials, terminal acceptors, or growth conditions. Using a panel of marker-free single, quadruple, and quintuple mutants, little support for these models could be found. Three quadruple mutants containing only one paralog (PpcA, PpcB, and PpcD) reduced Fe(III) citrate and Fe(III) oxide at the same rate and extent, even though PpcB and PpcD were at much lower periplasmic levels than PpcA. Mutants containing only PpcC and PpcE showed defects, but these cytochromes were nearly undetectable in the periplasm. When expressed sufficiently, PpcC and PpcE supported wild-type Fe(III) reduction. PpcA and PpcE from G. metallireducens similarly restored metal respiration in G. sulfurreducens. PgcA, an unrelated extracellular triheme c-type cytochrome, also participated in periplasmic electron transfer. While triheme cytochromes were important for metal reduction, sextuple ΔppcABCDE ΔpgcA mutants grew near wild-type rates with normal cyclic voltammetry profiles when using anodes as electron acceptors. These results reveal broad promiscuity in the periplasmic electron transfer network of metal-reducing Geobacter and suggest that an as-yet-undiscovered periplasmic mechanism supports electron transfer to electrodes. IMPORTANCE Many inner and outer membrane cytochromes used by Geobacter for electron transfer to extracellular acceptors have specific functions. How these are connected by periplasmic carriers remains poorly understood. G. sulfurreducens contains multiple triheme periplasmic cytochromes with unique biochemical properties and expression profiles. It is hypothesized that each could be involved in a different respiratory pathway, depending on redox potential or energy needs. Here, we show that Geobacter periplasmic cytochromes instead show evidence of being highly promiscuous. Any of 6 triheme cytochromes supported similar growth with soluble or insoluble metals, but none were required when cells utilized electrodes. These findings fail to support many models of Geobacter electron transfer, and question why these organisms produce such an array of periplasmic cytochromes.
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Affiliation(s)
- Sol Choi
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Chi Ho Chan
- BioTechnology Institute, University of Minnesota, Saint Paul, Minnesota, USA
| | - Daniel R. Bond
- BioTechnology Institute, University of Minnesota, Saint Paul, Minnesota, USA
- Department of Plant and Microbial Biology, University of Minnesota, Saint Paul, Minnesota, USA
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8
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He RL, Wu J, Cheng ZH, Li HH, Liu JQ, Liu DF, Li WW. Biomolecular Insights into Extracellular Pollutant Reduction Pathways of Geobacter sulfurreducens Using a Base Editor System. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:12247-12256. [PMID: 35960254 DOI: 10.1021/acs.est.2c02756] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Geobacter species are critically involved in elemental biogeochemical cycling and environmental bioremediation processes via extracellular electron transfer (EET), but the underlying biomolecular mechanisms remain elusive due to lack of effective analytical tools to explore into complicated EET networks. Here, a simple and highly efficient cytosine base editor was developed for engineering of the slow-growing Geobacter sulfurreducens (a doubling time of 5 h with acetate as the electron donor and fumarate as the electron acceptor). A single-plasmid cytosine base editor (pYYDT-BE) was constructed in G. sulfurreducens by fusing cytosine deaminase, Cas9 nickase, and a uracil glycosylase inhibitor. This system enabled single-locus editing at 100% efficiency and showed obvious preference at the cytosines in a TC, AC, or CC context than in a GC context. Gene inactivation tests confirmed that it could effectively edit 87.7-93.4% genes of the entire genome in nine model Geobacter species. With the aid of this base editor to construct a series of G. sulfurreducens mutants, we unveiled important roles of both pili and outer membrane c-type cytochromes in long-range EET, thereby providing important evidence to clarify the long-term controversy surrounding their specific roles. Furthermore, we find that pili were also involved in the extracellular reduction of uranium and clarified the key roles of the ExtHIJKL conduit complex and outer membrane c-type cytochromes in the selenite reduction process. This work developed an effective base editor tool for the genetic modification of Geobacter species and provided new insights into the EET network, which lay a basis for a better understanding and engineering of these microbes to favor environmental applications.
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Affiliation(s)
- Ru-Li He
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Jie Wu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
| | - Zhou-Hua Cheng
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
| | - Hui-Hui Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
| | - Jia-Qi Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
| | - Dong-Feng Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
| | - Wen-Wei Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science & Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou 215123, China
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9
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Wang F, Chan CH, Suciu V, Mustafa K, Ammend M, Si D, Hochbaum AI, Egelman EH, Bond DR. Structure of Geobacter OmcZ filaments suggests extracellular cytochrome polymers evolved independently multiple times. eLife 2022; 11:e81551. [PMID: 36062910 PMCID: PMC9473688 DOI: 10.7554/elife.81551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 09/03/2022] [Indexed: 11/26/2022] Open
Abstract
While early genetic and low-resolution structural observations suggested that extracellular conductive filaments on metal-reducing organisms such as Geobacter were composed of type IV pili, it has now been established that bacterial c-type cytochromes can polymerize to form extracellular filaments capable of long-range electron transport. Atomic structures exist for two such cytochrome filaments, formed from the hexaheme cytochrome OmcS and the tetraheme cytochrome OmcE. Due to the highly conserved heme packing within the central OmcS and OmcE cores, and shared pattern of heme coordination between subunits, it has been suggested that these polymers have a common origin. We have now used cryo-electron microscopy (cryo-EM) to determine the structure of a third extracellular filament, formed from the Geobacter sulfurreducens octaheme cytochrome, OmcZ. In contrast to the linear heme chains in OmcS and OmcE from the same organism, the packing of hemes, heme:heme angles, and between-subunit heme coordination is quite different in OmcZ. A branched heme arrangement within OmcZ leads to a highly surface exposed heme in every subunit, which may account for the formation of conductive biofilm networks, and explain the higher measured conductivity of OmcZ filaments. This new structural evidence suggests that conductive cytochrome polymers arose independently on more than one occasion from different ancestral multiheme proteins.
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Affiliation(s)
- Fengbin Wang
- Department of Biochemistry and Molecular Genetics, University of Virginia School of MedicineCharlottesvilleUnited States
| | - Chi Ho Chan
- Department of Plant and Microbial Biology, and BioTechnology Institute, University of MinnesotaSt. PaulUnited States
| | - Victor Suciu
- Division of Computing and Software Systems, University of Washington BothellBothellUnited States
| | - Khawla Mustafa
- Department of Chemistry, University of California, IrvineIrvineUnited States
| | - Madeline Ammend
- Department of Plant and Microbial Biology, and BioTechnology Institute, University of MinnesotaSt. PaulUnited States
| | - Dong Si
- Division of Computing and Software Systems, University of Washington BothellBothellUnited States
| | - Allon I Hochbaum
- Department of Chemistry, University of California, IrvineIrvineUnited States
- Department of Materials Science and Engineering, University of CaliforniaIrvineUnited States
- Department of Molecular Biology and Biochemistry, University of CaliforniaIrvineUnited States
- Department of Chemical and Biomolecular Engineering, University of CaliforniaIrvineUnited States
| | - Edward H Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia School of MedicineCharlottesvilleUnited States
| | - Daniel R Bond
- Department of Plant and Microbial Biology, and BioTechnology Institute, University of MinnesotaSt. PaulUnited States
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10
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Cryo-EM structure of an extracellular Geobacter OmcE cytochrome filament reveals tetrahaem packing. Nat Microbiol 2022; 7:1291-1300. [PMID: 35798889 PMCID: PMC9357133 DOI: 10.1038/s41564-022-01159-z] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 05/23/2022] [Indexed: 12/11/2022]
Abstract
Electrically conductive appendages from the anaerobic bacterium Geobacter sulfurreducens were first observed two decades ago, with genetic and biochemical data suggesting that conductive fibres were type IV pili. Recently, an extracellular conductive filament of G. sulfurreducens was found to contain polymerized c-type cytochrome OmcS subunits, not pilin subunits. Here we report that G. sulfurreducens also produces a second, thinner appendage comprised of cytochrome OmcE subunits and solve its structure using cryo-electron microscopy at ~4.3 Å resolution. Although OmcE and OmcS subunits have no overall sequence or structural similarities, upon polymerization both form filaments that share a conserved haem packing arrangement in which haems are coordinated by histidines in adjacent subunits. Unlike OmcS filaments, OmcE filaments are highly glycosylated. In extracellular fractions from G. sulfurreducens, we detected type IV pili comprising PilA-N and -C chains, along with abundant B-DNA. OmcE is the second cytochrome filament to be characterized using structural and biophysical methods. We propose that there is a broad class of conductive bacterial appendages with conserved haem packing (rather than sequence homology) that enable long-distance electron transport to chemicals or other microbial cells.
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11
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GSU1771 regulates extracellular electron transfer and electroactive biofilm formation in Geobacter sulfurreducens: Genetic and electrochemical characterization. Bioelectrochemistry 2022; 145:108101. [PMID: 35334296 DOI: 10.1016/j.bioelechem.2022.108101] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2021] [Revised: 03/15/2022] [Accepted: 03/16/2022] [Indexed: 11/21/2022]
Abstract
Type IV pili and the >100c-type cytochromes in Geobacter sulfurreducens are essential for extracellular electron transfer (EET) towards metal oxides and electrodes. A previous report about a mutation in the gsu1771 gene indicated an enhanced reduction of insoluble Fe(III) oxides coupled with increased pilA expression. Herein, a marker-free gsu1771-deficient mutant was constructed and characterized to assess the role of this regulator in EET and the formation of electroactive biofilms. Deleting this gene delayed microbial growth in the acetate/fumarate media (electron donor and acceptor, respectively). However, this mutant reduced soluble and insoluble Fe(III) oxides more efficiently. Heme staining, western blot, and RT-qPCR analyses demonstrated that GSU1771 regulates the transcription of several genes (including pilA) and many c-type cytochromes involved in EET, suggesting the broad regulatory role of this protein. DNA-protein binding assays indicated that GSU1771 directly regulates the transcription of pilA, omcE, omcS, and omcZ. Additionally, gsu1771-deficient mutant biofilms are thicker than wild-type strains. Electrochemical studies revealed that the current produced by this biofilm was markedly higher than the wild-type strains (approximately 100-fold). Thus, demonstrating the role of GSU1771 in the EET pathway and establishing a methodology to develop highly electroactive G. sulfurreducens mutants.
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The Signaling Pathway That cGAMP Riboswitches Found: Analysis and Application of Riboswitches to Study cGAMP Signaling in Geobacter sulfurreducens. Int J Mol Sci 2022; 23:ijms23031183. [PMID: 35163114 PMCID: PMC8835794 DOI: 10.3390/ijms23031183] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 01/12/2022] [Accepted: 01/14/2022] [Indexed: 02/03/2023] Open
Abstract
The Hypr cGAMP signaling pathway was discovered via the function of the riboswitch. In this study, we show the development of a method for affinity capture followed by sequencing to identify non-coding RNA regions that bind nucleotide signals such as cGAMP. The RNAseq of affinity-captured cGAMP riboswitches from the Geobacter sulfurreducens transcriptome highlights general challenges that remain for this technique. Furthermore, by applying riboswitch reporters in vivo, we identify new growth conditions and transposon mutations that affect cGAMP levels in G. sulfurreducens. This work reveals an extensive regulatory network and supports a second functional cGAMP synthase gene in G. sulfurreducens. The activity of the second synthase was validated using riboswitch-based fluorescent biosensors, and is the first known example of an active enzyme with a variant GGDDF motif.
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13
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Wu J, Liu DF, Li HH, Min D, Liu JQ, Xu P, Li WW, Yu HQ, Zhu YG. Controlling pathogenic risks of water treatment biotechnologies at the source by genetic editing means. Environ Microbiol 2021; 23:7578-7590. [PMID: 34837302 DOI: 10.1111/1462-2920.15851] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Revised: 11/10/2021] [Accepted: 11/12/2021] [Indexed: 11/27/2022]
Abstract
Antimicrobial-resistant pathogens in the environment and wastewater treatment systems, many of which are also important pollutant degraders and are difficult to control by traditional disinfection approaches, have become an unprecedented treat to ecological security and human health. Here, we propose the adoption of genetic editing techniques as a highly targeted, efficient and simple tool to control the risks of environmental pathogens at the source. An 'all-in-one' plasmid system was constructed in Aeromonas hydrophila to accurately identify and selectively inactivate multiple key virulence factor genes and antibiotic resistance genes via base editing, enabling significantly suppressed bacterial virulence and resistance without impairing their normal phenotype and pollutant-degradation functions. Its safe application for bioaugmented treatment of synthetic textile wastewater was also demonstrated. This genetic-editing technique may offer a promising solution to control the health risks of environmental microorganisms via targeted gene inactivation, thereby facilitating safer application of water treatment biotechnologies.
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Affiliation(s)
- Jie Wu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China.,University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou, 215123, China
| | - Dong-Feng Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China.,Anhui Key Laboratory of Sewage Purification and Ecological Rehabilitation Materials, Hefei, 230601, China
| | - Hui-Hui Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
| | - Di Min
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
| | - Jia-Qi Liu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
| | - Peng Xu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
| | - Wen-Wei Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China.,University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou Institute for Advance Research of USTC, Suzhou, 215123, China
| | - Han-Qing Yu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Environmental Science and Engineering, University of Science and Technology of China, Hefei, 230026, China
| | - Yong-Guan Zhu
- CAS Key Laboratory of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.,State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-environmental Sciences, Chinese Academy of Sciences, Beijing, China
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14
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Bird LJ, Kundu BB, Tschirhart T, Corts AD, Su L, Gralnick JA, Ajo-Franklin CM, Glaven SM. Engineering Wired Life: Synthetic Biology for Electroactive Bacteria. ACS Synth Biol 2021; 10:2808-2823. [PMID: 34637280 DOI: 10.1021/acssynbio.1c00335] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Electroactive bacteria produce or consume electrical current by moving electrons to and from extracellular acceptors and donors. This specialized process, known as extracellular electron transfer, relies on pathways composed of redox active proteins and biomolecules and has enabled technologies ranging from harvesting energy on the sea floor, to chemical sensing, to carbon capture. Harnessing and controlling extracellular electron transfer pathways using bioengineering and synthetic biology promises to heighten the limits of established technologies and open doors to new possibilities. In this review, we provide an overview of recent advancements in genetic tools for manipulating native electroactive bacteria to control extracellular electron transfer. After reviewing electron transfer pathways in natively electroactive organisms, we examine lessons learned from the introduction of extracellular electron transfer pathways into Escherichia coli. We conclude by presenting challenges to future efforts and give examples of opportunities to bioengineer microbes for electrochemical applications.
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Affiliation(s)
- Lina J. Bird
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Biki B. Kundu
- PhD Program in Systems, Synthetic, and Physical Biology, Rice University, Houston, Texas 77005, United States
| | - Tanya Tschirhart
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Anna D. Corts
- Joyn Bio, Boston, Massachusetts 02210, United States
| | - Lin Su
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210018, People’s Republic of China
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Jeffrey A. Gralnick
- Department of Plant and Microbial Biology, BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108, United States
| | | | - Sarah M. Glaven
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
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15
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Fujikawa T, Ogura Y, Ishigami K, Kawano Y, Nagamine M, Hayashi T, Inoue K. Unexpected genomic features of high current density-producing Geobacter sulfurreducens strain YM18. FEMS Microbiol Lett 2021; 368:6362602. [PMID: 34472610 DOI: 10.1093/femsle/fnab119] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2021] [Accepted: 08/31/2021] [Indexed: 12/28/2022] Open
Abstract
Geobacter sulfurreducens produces high current densities and it has been used as a model organism for extracellular electron transfer studies. Nine G. sulfurreducens strains were isolated from biofilms formed on an anode poised at -0.2 V (vs SHE) in a bioelectrochemical system in which river sediment was used as an inoculum. The maximum current density of an isolate, strain YM18 (9.29 A/m2), was higher than that of the strain PCA (5.72 A/m2), the type strain of G. sulfurreducens, and comparable to strain KN400 (8.38 A/m2), which is another high current-producing strain of G. sulfurreducens. Genomic comparison of strains PCA, KN400 and YM18 revealed that omcB, xapD, spc and ompJ, which are known to be important genes for iron reduction and current production in PCA, were not present in YM18. In the PCA and KN400 genomes, two and one region(s) encoding CRISPR/Cas systems were identified, respectively, but they were missing in the YM18 genome. These results indicate that there is genetic variation in the key components involved in extracellular electron transfer among G. sulfurreducens strains.
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Affiliation(s)
- Takashi Fujikawa
- Interdisciplinary Graduate School of Agriculture and Engineering, University of Miyazaki, Miyazaki 889-2192, Japan
| | - Yoshitoshi Ogura
- Division of Microbiology, Department of Infectious Medicine, Kurume University School of Medicine, Kurume 830-0011, Fukuoka, Japan
| | - Koki Ishigami
- Department of Biochemistry and Applied Biosciences, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
| | - Yoshihiro Kawano
- Department of Biochemistry and Applied Biosciences, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
| | - Miyuki Nagamine
- Department of Biochemistry and Applied Biosciences, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
| | - Tetsuya Hayashi
- Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Fukuoka 812-8285, Japan
| | - Kengo Inoue
- Department of Biochemistry and Applied Biosciences, Faculty of Agriculture, University of Miyazaki, Miyazaki 889-2192, Japan
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16
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Structure of Geobacter pili reveals secretory rather than nanowire behaviour. Nature 2021; 597:430-434. [PMID: 34471289 PMCID: PMC9127704 DOI: 10.1038/s41586-021-03857-w] [Citation(s) in RCA: 86] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 07/28/2021] [Indexed: 02/07/2023]
Abstract
Extracellular electron transfer by Geobacter species through surface appendages known as microbial nanowires1 is important in a range of globally important environmental phenomena2, as well as for applications in bio-remediation, bioenergy, biofuels and bioelectronics. Since 2005, these nanowires have been thought to be type 4 pili composed solely of the PilA-N protein1. However, previous structural analyses have demonstrated that, during extracellular electron transfer, cells do not produce pili but rather nanowires made up of the cytochromes OmcS2,3 and OmcZ4. Here we show that Geobacter sulfurreducens binds PilA-N to PilA-C to assemble heterodimeric pili, which remain periplasmic under nanowire-producing conditions that require extracellular electron transfer5. Cryo-electron microscopy revealed that C-terminal residues of PilA-N stabilize its copolymerization with PilA-C (to form PilA-N-C) through electrostatic and hydrophobic interactions that position PilA-C along the outer surface of the filament. PilA-N-C filaments lack π-stacking of aromatic side chains and show a conductivity that is 20,000-fold lower than that of OmcZ nanowires. In contrast with surface-displayed type 4 pili, PilA-N-C filaments show structure, function and localization akin to those of type 2 secretion pseudopili6. The secretion of OmcS and OmcZ nanowires is lost when pilA-N is deleted and restored when PilA-N-C filaments are reconstituted. The substitution of pilA-N with the type 4 pili of other microorganisms also causes a loss of secretion of OmcZ nanowires. As all major phyla of prokaryotes use systems similar to type 4 pili, this nanowire translocation machinery may have a widespread effect in identifying the evolution and prevalence of diverse electron-transferring microorganisms and in determining nanowire assembly architecture for designing synthetic protein nanowires.
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17
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Joshi K, Chan CH, Bond DR. Geobacter sulfurreducens inner membrane cytochrome CbcBA controls electron transfer and growth yield near the energetic limit of respiration. Mol Microbiol 2021; 116:1124-1139. [PMID: 34423503 DOI: 10.1111/mmi.14801] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 08/18/2021] [Accepted: 08/19/2021] [Indexed: 12/24/2022]
Abstract
Geobacter sulfurreducens utilizes extracellular electron acceptors such as Mn(IV), Fe(III), syntrophic partners, and electrodes that vary from +0.4 to -0.3 V versus standard hydrogen electrode (SHE), representing a potential energy span that should require a highly branched electron transfer chain. Here we describe CbcBA, a bc-type cytochrome essential near the thermodynamic limit of respiration when acetate is the electron donor. Mutants-lacking cbcBA ceased Fe(III) reduction at -0.21 V versus SHE, could not transfer electrons to electrodes between -0.21 and -0.28 V, and could not reduce the final 10%-35% of Fe(III) minerals. As redox potential decreased during Fe(III) reduction, cbcBA was induced with the aid of the regulator BccR to become one of the most highly expressed genes in G. sulfurreducens. Growth yield (CFU/mM Fe(II)) was 112% of WT in ∆cbcBA, and deletion of cbcL (an unrelated bc-cytochrome essential near -0.15 V) in ΔcbcBA increased yield to 220%. Together with ImcH, which is required at high redox potentials, CbcBA represents a third cytoplasmic membrane oxidoreductase in G. sulfurreducens. This expanding list shows how metal-reducing bacteria may constantly sense redox potential to adjust growth efficiency in changing environments.
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Affiliation(s)
- Komal Joshi
- The BioTechnology Institute, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA.,Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Chi Ho Chan
- The BioTechnology Institute, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
| | - Daniel R Bond
- The BioTechnology Institute, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA.,Department of Plant and Microbial Biology, University of Minnesota Twin Cities, Minneapolis, Minnesota, USA
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18
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Evidence of a Streamlined Extracellular Electron Transfer Pathway from Biofilm Structure, Metabolic Stratification, and Long-Range Electron Transfer Parameters. Appl Environ Microbiol 2021; 87:e0070621. [PMID: 34190605 PMCID: PMC8357294 DOI: 10.1128/aem.00706-21] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
A strain of Geobacter sulfurreducens, an organism capable of respiring solid extracellular substrates, lacking four of five outer membrane cytochrome complexes (extABCD+ strain) grows faster and produces greater current density than the wild type grown under identical conditions. To understand cellular and biofilm modifications in the extABCD+ strain responsible for this increased performance, biofilms grown using electrodes as terminal electron acceptors were sectioned and imaged using electron microscopy to determine changes in thickness and cell density, while parallel biofilms incubated in the presence of nitrogen and carbon isotopes were analyzed using NanoSIMS (nanoscale secondary ion mass spectrometry) to quantify and localize anabolic activity. Long-distance electron transfer parameters were measured for wild-type and extABCD+ biofilms spanning 5-μm gaps. Our results reveal that extABCD+ biofilms achieved higher current densities through the additive effects of denser cell packing close to the electrode (based on electron microscopy), combined with higher metabolic rates per cell compared to the wild type (based on increased rates of 15N incorporation). We also observed an increased rate of electron transfer through extABCD+ versus wild-type biofilms, suggesting that denser biofilms resulting from the deletion of unnecessary multiheme cytochromes streamline electron transfer to electrodes. The combination of imaging, physiological, and electrochemical data confirms that engineered electrogenic bacteria are capable of producing more current per cell and, in combination with higher biofilm density and electron diffusion rates, can produce a higher final current density than the wild type. IMPORTANCE Current-producing biofilms in microbial electrochemical systems could potentially sustain technologies ranging from wastewater treatment to bioproduction of electricity if the maximum current produced could be increased and current production start-up times after inoculation could be reduced. Enhancing the current output of microbial electrochemical systems has been mostly approached by engineering physical components of reactors and electrodes. Here, we show that biofilms formed by a Geobacter sulfurreducens strain producing ∼1.4× higher current than the wild type results from a combination of denser cell packing and higher anabolic activity, enabled by an increased rate of electron diffusion through the biofilms. Our results confirm that it is possible to engineer electrode-specific G. sulfurreducens strains with both faster growth on electrodes and streamlined electron transfer pathways for enhanced current production.
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19
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Boedicker JQ, Gangan M, Naughton K, Zhao F, Gralnick JA, El-Naggar MY. Engineering Biological Electron Transfer and Redox Pathways for Nanoparticle Synthesis. Bioelectricity 2021; 3:126-135. [PMID: 34476388 DOI: 10.1089/bioe.2021.0010] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Many species of bacteria are naturally capable of types of electron transport not observed in eukaryotic cells. Some species live in environments containing heavy metals not typically encountered by cells of multicellular organisms, such as arsenic, cadmium, and mercury, leading to the evolution of enzymes to deal with these environmental toxins. Bacteria also inhabit a variety of extreme environments, and are capable of respiration even in the absence of oxygen as a terminal electron acceptor. Over the years, several of these exotic redox and electron transport pathways have been discovered and characterized in molecular-level detail, and more recently synthetic biology has begun to utilize these pathways to engineer cells capable of detecting and processing a variety of metals and semimetals. One such application is the biologically controlled synthesis of nanoparticles. This review will introduce the basic concepts of bacterial metal reduction, summarize recent work in engineering bacteria for nanoparticle production, and highlight the most cutting-edge work in the characterization and application of bacterial electron transport pathways.
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Affiliation(s)
- James Q Boedicker
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, USA.,Department of Biological Sciences, University of Southern California, Los Angeles, California, USA
| | - Manasi Gangan
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, USA
| | - Kyle Naughton
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, USA
| | - Fengjie Zhao
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, USA
| | - Jeffrey A Gralnick
- BioTechnology Institute, University of Minnesota-Twin Cities, St. Paul, Minnesota, USA.,Department of Plant and Microbial Biology, University of Minnesota-Twin Cities, St. Paul, Minnesota, USA
| | - Mohamed Y El-Naggar
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, USA.,Department of Biological Sciences, University of Southern California, Los Angeles, California, USA.,Department of Chemistry, University of Southern California, Los Angeles, California, USA
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20
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Engineering Cooperation in an Anaerobic Coculture. Appl Environ Microbiol 2021; 87:AEM.02852-20. [PMID: 33771781 DOI: 10.1128/aem.02852-20] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Accepted: 03/19/2021] [Indexed: 01/28/2023] Open
Abstract
Over the past century, microbiologists have studied organisms in pure culture, yet it is becoming increasingly apparent that the majority of biological processes rely on multispecies cooperation and interaction. While little is known about how such interactions permit cooperation, even less is known about how cooperation arises. To study the emergence of cooperation in the laboratory, we constructed both a commensal community and an obligate mutualism using the previously noninteracting bacteria Shewanella oneidensis and Geobacter sulfurreducens Incorporation of a glycerol utilization plasmid (pGUT2) enabled S. oneidensis to metabolize glycerol and produce acetate as a carbon source for G. sulfurreducens, establishing a cross-feeding, commensal coculture. In the commensal coculture, both species coupled oxidative metabolism to the respiration of fumarate as the terminal electron acceptor. Deletion of the gene encoding fumarate reductase in the S. oneidensis/pGUT2 strain shifted the coculture with G. sulfurreducens to an obligate mutualism where neither species could grow in the absence of the other. A shift in metabolic strategy from glycerol catabolism to malate metabolism was associated with obligate coculture growth. Further targeted deletions in malate uptake and acetate generation pathways in S. oneidensis significantly inhibited coculture growth with G. sulfurreducens The engineered coculture between S. oneidensis and G. sulfurreducens provides a model laboratory system to study the emergence of cooperation in bacterial communities, and the shift in metabolic strategy observed in the obligate coculture highlights the importance of genetic change in shaping microbial interactions in the environment.IMPORTANCE Microbes seldom live alone in the environment, yet this scenario is approximated in the vast majority of pure-culture laboratory experiments. Here, we develop an anaerobic coculture system to begin understanding microbial physiology in a more complex setting but also to determine how anaerobic microbial communities can form. Using synthetic biology, we generated a coculture system where the facultative anaerobe Shewanella oneidensis consumes glycerol and provides acetate to the strict anaerobe Geobacter sulfurreducens In the commensal system, growth of G. sulfurreducens is dependent on the presence of S. oneidensis To generate an obligate coculture, where each organism requires the other, we eliminated the ability of S. oneidensis to respire fumarate. An unexpected shift in metabolic strategy from glycerol catabolism to malate metabolism was observed in the obligate coculture. Our work highlights how metabolic landscapes can be expanded in multispecies communities and provides a system to evaluate the evolution of cooperation under anaerobic conditions.
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Andrade A, Hernández-Eligio A, Tirado AL, Vega-Alvarado L, Olvera M, Morett E, Juárez K. Specialization of the Reiterated Copies of the Heterodimeric Integration Host Factor Genes in Geobacter sulfurreducens. Front Microbiol 2021; 12:626443. [PMID: 33737919 PMCID: PMC7962754 DOI: 10.3389/fmicb.2021.626443] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Accepted: 01/14/2021] [Indexed: 12/13/2022] Open
Abstract
Integration host factor (IHF) is a widely distributed small heterodimeric protein member of the bacterial Nucleoid-Associated Proteins (NAPs), implicated in multiple DNA regulatory processes. IHF recognizes a specific DNA sequence and induces a large bend of the nucleic acid. IHF function has been mainly linked with the regulation of RpoN-dependent promoters, where IHF commonly recognizes a DNA sequence between the enhancer-binding region and the promoter, facilitating a close contact between the upstream bound activator and the promoter bound, RNA polymerase. In most proteobacteria, the genes encoding IHF subunits (ihfA and ihfB) are found in a single copy. However, in some Deltaproteobacteria, like Geobacter sulfurreducens, those genes are duplicated. To date, the functionality of IHF reiterated encoding genes is unknown. In this work, we achieved the functional characterization of the ihfA-1, ihfA-2, ihfB-1, and ihfB-2 from G. sulfurreducens. Unlike the ΔihfA-2 or ΔihfB-1 strains, single gene deletion in ihfA-1 or ihfB-2, provokes an impairment in fumarate and Fe(III) citrate reduction. Accordingly, sqRT-PCR experiments showed that ihfA-1 and ihfB-2 were expressed at higher levels than ihfA-2 and ihfB-1. In addition, RNA-Seq analysis of the ΔihfA-1 and ΔihfB-2 strains revealed a total of 89 and 122 differentially expressed genes, respectively. Furthermore, transcriptional changes in 25 genes were shared in both mutant strains. Among these genes, we confirmed the upregulation of the pilA-repressor, GSU1771, and downregulation of the triheme-cytochrome (pgcA) and the aconitate hydratase (acnA) genes by RT-qPCR. EMSA experiments also demonstrated the direct binding of IHF to the upstream promoter regions of GSU1771, pgcA and acnA. PilA changes in ΔihfA-1 and ΔihfB-2 strains were also verified by immunoblotting. Additionally, heme-staining of subcellular fractions in ΔihfA-1 and ΔihfB-2 strains revealed a remarkable deficit of c-type cytochromes. Overall, our data indicate that at least during fumarate and Fe(III) citrate reduction, the functional IHF regulator is likely assembled by the products of ihfA-1 and ihfB-2. Also, a role of IHF controlling expression of multiple genes (other than RpoN-dependent) affects G. sulfurreducens physiology and extracellular electron transfer.
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Affiliation(s)
- Angel Andrade
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico.,Departamento de Microbiología, Facultad de Medicina, Universidad Autónoma de Nuevo León, Monterrey, Mexico
| | - Alberto Hernández-Eligio
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico.,CONACYT, Ciudad de México, Mexico
| | - Ana Lilia Tirado
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Leticia Vega-Alvarado
- Instituto de Ciencias Aplicadas y Tecnología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, Mexico
| | - Maricela Olvera
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Enrique Morett
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
| | - Katy Juárez
- Departamento de Ingeniería Celular y Biocatálisis, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, Mexico
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22
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Engineering lithoheterotrophy in an obligate chemolithoautotrophic Fe(II) oxidizing bacterium. Sci Rep 2021; 11:2165. [PMID: 33495498 PMCID: PMC7835226 DOI: 10.1038/s41598-021-81412-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2020] [Accepted: 01/04/2021] [Indexed: 11/09/2022] Open
Abstract
Neutrophilic Fe(II) oxidizing bacteria like Mariprofundus ferrooxydans are obligate chemolithoautotrophic bacteria that play an important role in the biogeochemical cycling of iron and other elements in multiple environments. These bacteria generally exhibit a singular metabolic mode of growth which prohibits comparative "omics" studies. Furthermore, these bacteria are considered non-amenable to classical genetic methods due to low cell densities, the inability to form colonies on solid medium, and production of copious amounts of insoluble iron oxyhydroxides as their metabolic byproduct. Consequently, the molecular and biochemical understanding of these bacteria remains speculative despite the availability of substantial genomic information. Here we develop the first genetic system in neutrophilic Fe(II) oxidizing bacterium and use it to engineer lithoheterotrophy in M. ferrooxydans, a metabolism that has been speculated but not experimentally validated. This synthetic biology approach could be extended to gain physiological understanding and domesticate other bacteria that grow using a single metabolic mode.
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23
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Li J, Tang Q, Li Y, Fan YY, Li FH, Wu JH, Min D, Li WW, Lam PKS, Yu HQ. Rediverting Electron Flux with an Engineered CRISPR-ddAsCpf1 System to Enhance the Pollutant Degradation Capacity of Shewanella oneidensis. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:3599-3608. [PMID: 32062962 DOI: 10.1021/acs.est.9b06378] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Pursuing efficient approaches to promote the extracellular electron transfer (EET) of extracellular respiratory bacteria is essential to their application in environmental remediation and waste treatment. Here, we report a new strategy of tuning electron flux by clustered regularly interspaced short palindromic repeat (CRISPR)-ddAsCpf1-based rediverting (namely STAR) to enhance the EET capacity of Shewanella oneidensis MR-1, a model extracellular respiratory bacterium widely present in the environment. The developed CRISPR-ddAsCpf1 system enabled approximately 100% gene repression with the green fluorescent protein (GFP) as a reporter. Using a WO3 probe, 10 representative genes encoding for putative competitive electron transfer proteins were screened, among which 7 genes were identified as valid targets for EET enhancement. Repressing the valid genes not only increased the transcription level of the l-lactate metabolism genes but also affected the genes involved in direct and indirect EET. Increased riboflavin production was also observed. The feasibility of this strategy to enhance the bioreduction of methyl orange, an organic pollutant, and chromium, a typical heavy metal, was demonstrated. This work implies a great potential of the STAR strategy with the CIRPSR-ddAsCpf1 system for enhancing bacterial EET to favor more efficient environmental remediation applications.
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Affiliation(s)
- Jie Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou 215123, China
- State Key Laboratory in Marine Pollution, Department of Chemistry, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
| | - Qiang Tang
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Yang Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Yang-Yang Fan
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Feng-He Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Jing-Hang Wu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Di Min
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Wen-Wei Li
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou 215123, China
| | - Paul K S Lam
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou 215123, China
- State Key Laboratory in Marine Pollution, Department of Chemistry, City University of Hong Kong, Kowloon 999077, Hong Kong SAR, China
| | - Han-Qing Yu
- CAS Key Laboratory of Urban Pollutant Conversion, Department of Applied Chemistry, University of Science and Technology of China, Hefei 230026, China
- University of Science and Technology of China-City University of Hong Kong Joint Advanced Research Center, Suzhou 215123, China
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24
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Nora LC, Westmann CA, Guazzaroni ME, Siddaiah C, Gupta VK, Silva-Rocha R. Recent advances in plasmid-based tools for establishing novel microbial chassis. Biotechnol Adv 2019; 37:107433. [PMID: 31437573 DOI: 10.1016/j.biotechadv.2019.107433] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 07/11/2019] [Accepted: 08/16/2019] [Indexed: 12/28/2022]
Abstract
A key challenge for domesticating alternative cultivable microorganisms with biotechnological potential lies in the development of innovative technologies. Within this framework, a myriad of genetic tools has flourished, allowing the design and manipulation of complex synthetic circuits and genomes to become the general rule in many laboratories rather than the exception. More recently, with the development of novel technologies such as DNA automated synthesis/sequencing and powerful computational tools, molecular biology has entered the synthetic biology era. In the beginning, most of these technologies were established in traditional microbial models (known as chassis in the synthetic biology framework) such as Escherichia coli and Saccharomyces cerevisiae, enabling fast advances in the field and the validation of fundamental proofs of concept. However, it soon became clear that these organisms, although extremely useful for prototyping many genetic tools, were not ideal for a wide range of biotechnological tasks due to intrinsic limitations in their molecular/physiological properties. Over the last decade, researchers have been facing the great challenge of shifting from these model systems to non-conventional chassis with endogenous capacities for dealing with specific tasks. The key to address these issues includes the generation of narrow and broad host plasmid-based molecular tools and the development of novel methods for engineering genomes through homologous recombination systems, CRISPR/Cas9 and other alternative methods. Here, we address the most recent advances in plasmid-based tools for the construction of novel cell factories, including a guide for helping with "build-your-own" microbial host.
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Affiliation(s)
- Luísa Czamanski Nora
- Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - Cauã Antunes Westmann
- Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | - María-Eugenia Guazzaroni
- Faculty of Philosophy, Science and Letters of Ribeirão Preto, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil
| | | | - Vijai Kumar Gupta
- ERA Chair of Green Chemistry, Department of Chemistry and Biotechnology, School of Science, Tallinn University of Technology, 12618 Tallinn, Estonia
| | - Rafael Silva-Rocha
- Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo 14049-900, Brazil.
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25
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Hallberg ZF, Chan CH, Wright TA, Kranzusch PJ, Doxzen KW, Park JJ, Bond DR, Hammond MC. Structure and mechanism of a Hypr GGDEF enzyme that activates cGAMP signaling to control extracellular metal respiration. eLife 2019; 8:43959. [PMID: 30964001 PMCID: PMC6456294 DOI: 10.7554/elife.43959] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 03/12/2019] [Indexed: 12/16/2022] Open
Abstract
A newfound signaling pathway employs a GGDEF enzyme with unique activity compared to the majority of homologs associated with bacterial cyclic di-GMP signaling. This system provides a rare opportunity to study how signaling proteins natively gain distinct function. Using genetic knockouts, riboswitch reporters, and RNA-Seq, we show that GacA, the Hypr GGDEF in Geobacter sulfurreducens, specifically regulates cyclic GMP-AMP (3′,3′-cGAMP) levels in vivo to stimulate gene expression associated with metal reduction separate from electricity production. To reconcile these in vivo findings with prior in vitro results that showed GacA was promiscuous, we developed a full kinetic model combining experimental data and mathematical modeling to reveal mechanisms that contribute to in vivo specificity. A 1.4 Å-resolution crystal structure of the Geobacter Hypr GGDEF domain was determined to understand the molecular basis for those mechanisms, including key cross-dimer interactions. Together these results demonstrate that specific signaling can result from a promiscuous enzyme. Microscopic organisms known as bacteria are found in virtually every environment on the planet. One reason bacteria are so successful is that they are able to form communities known as biofilms on surfaces in animals and other living things, as well as on rocks and other features in the environment. These biofilms protect the bacteria from fluctuations in the environment and toxins. For over 30 years, a class of enzymes called the GGDEF enzymes were thought to make a single signal known as cyclic di-GMP that regulates the formation of biofilms. However, in 2016, a team of researchers reported that some GGDEF enzymes, including one from a bacterium called Geobacter sulfurreducens, were also able to produce two other signals known as cGAMP and cyclic di-AMP. The experiments involved making the enzymes and testing their activity outside the cell. Therefore, it remained unclear whether these enzymes (dubbed ‘Hypr’ GGDEF enzymes) actually produce all three signals inside cells and play a role in forming bacterial biofilms. G. sulfurreducens is unusual because it is able to grow on metallic minerals or electrodes to generate electrical energy. As part of a community of microorganisms, they help break down pollutants in contaminated areas and can generate electricity from wastewater. Now, Hallberg, Chan et al. – including many of the researchers involved in the 2016 work – combined several experimental and mathematical approaches to study the Hypr GGDEF enzymes in G. sulfurreducens. The experiments show that the Hypr GGDEF enzymes produced cGAMP, but not the other two signals, inside the cells. This cGAMP regulated the ability of G. sulfurreducens to grow by extracting electrical energy from the metallic minerals, which appears to be a new, biofilm-less lifestyle. Further experiments revealed how Hypr GGDEF enzymes have evolved to preferentially make cGAMP over the other two signals. Together, these findings demonstrate that enzymes with the ability to make several different signals, are capable of generating specific responses in bacterial cells. By understanding how bacteria make decisions, it may be possible to change their behaviors. The findings of Hallberg, Chan et al. help to identify the signaling pathways involved in this decision-making and provide new tools to study them in the future.
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Affiliation(s)
- Zachary F Hallberg
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Chi Ho Chan
- Department of Plant and Microbial Biology and BioTechnology Institute, University of Minnesota, Minnesota, United States
| | - Todd A Wright
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Philip J Kranzusch
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, United States.,Department of Cancer Immunology and Virology, Dana-Farber Cancer Institute, Boston, United States.,Parker Institute for Cancer Immunotherapy at Dana-Farber Cancer Institute, Boston, United States
| | - Kevin W Doxzen
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, United States
| | - James J Park
- Department of Chemistry, University of California, Berkeley, Berkeley, United States
| | - Daniel R Bond
- Department of Plant and Microbial Biology and BioTechnology Institute, University of Minnesota, Minnesota, United States
| | - Ming C Hammond
- Department of Chemistry, University of California, Berkeley, Berkeley, United States.,Department of Molecular & Cell Biology, University of California, Berkeley, Berkeley, United States.,Department of Chemistry, University of Utah, Salt Lake City, United States
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26
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Divergent Nrf Family Proteins and MtrCAB Homologs Facilitate Extracellular Electron Transfer in Aeromonas hydrophila. Appl Environ Microbiol 2018; 84:AEM.02134-18. [PMID: 30266730 DOI: 10.1128/aem.02134-18] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 09/26/2018] [Indexed: 01/05/2023] Open
Abstract
Extracellular electron transfer (EET) is a strategy for respiration in which electrons generated from metabolism are moved outside the cell to a terminal electron acceptor, such as iron or manganese oxide. EET has primarily been studied in two model systems, Shewanella oneidensis and Geobacter sulfurreducens Metal reduction has also been reported in numerous microorganisms, including Aeromonas spp., which are ubiquitous Gammaproteobacteria found in aquatic ecosystems, with some species capable of pathogenesis in humans and fish. Genomic comparisons of Aeromonas spp. revealed a potential outer membrane conduit homologous to S. oneidensis MtrCAB. While the ability to respire metals and mineral oxides is not widespread in the genus Aeromonas, 90% of the sequenced Aeromonas hydrophila isolates contain MtrCAB homologs. A. hydrophila ATCC 7966 mutants lacking mtrA are unable to reduce metals. Expression of A. hydrophila mtrCAB in an S. oneidensis mutant lacking homologous components restored metal reduction. Although the outer membrane conduits for metal reduction were similar, homologs of the S. oneidensis inner membrane and periplasmic EET components CymA, FccA, and CctA were not found in A. hydrophila We characterized a cluster of genes predicted to encode components related to a formate-dependent nitrite reductase (NrfBCD), here named NetBCD (for Nrf-like electron transfer), and a predicted diheme periplasmic cytochrome, PdsA (periplasmic diheme shuttle). We present genetic evidence that proteins encoded by this cluster facilitate electron transfer from the cytoplasmic membrane across the periplasm to the MtrCAB conduit and function independently from an authentic NrfABCD system. A. hydrophila mutants lacking pdsA and netBCD were unable to reduce metals, while heterologous expression of these genes could restore metal reduction in an S. oneidensis mutant background. EET may therefore allow A. hydrophila and other species of Aeromonas to persist and thrive in iron- or manganese-rich oxygen-limited environments.IMPORTANCE Metal-reducing microorganisms are used for electricity production, bioremediation of toxic compounds, wastewater treatment, and production of valuable compounds. Despite numerous microorganisms being reported to reduce metals, the molecular mechanism has primarily been studied in two model systems, Shewanella oneidensis and Geobacter sulfurreducens We have characterized the mechanism of extracellular electron transfer in Aeromonas hydrophila, which uses the well-studied Shewanella system, MtrCAB, to move electrons across the outer membrane; however, most Aeromonas spp. appear to use a novel mechanism to transfer electrons from the inner membrane through the periplasm and to the outer membrane. The conserved use of MtrCAB in Shewanella spp. and Aeromonas spp. for metal reduction and conserved genomic architecture of metal reduction genes in Aeromonas spp. may serve as genomic markers for identifying metal-reducing microorganisms from genomic or transcriptomic sequencing. Understanding the variety of pathways used to reduce metals can allow for optimization and more efficient design of microorganisms used for practical applications.
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27
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Identification of Different Putative Outer Membrane Electron Conduits Necessary for Fe(III) Citrate, Fe(III) Oxide, Mn(IV) Oxide, or Electrode Reduction by Geobacter sulfurreducens. J Bacteriol 2018; 200:JB.00347-18. [PMID: 30038047 PMCID: PMC6148476 DOI: 10.1128/jb.00347-18] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Accepted: 07/17/2018] [Indexed: 12/14/2022] Open
Abstract
Gram-negative metal-reducing bacteria utilize electron conduits, chains of redox proteins spanning the outer membrane, to transfer electrons to the extracellular surface. Only one pathway for electron transfer across the outer membrane of Geobacter sulfurreducens has been linked to Fe(III) reduction. However, G. sulfurreducens is able to respire a wide array of extracellular substrates. Here we present the first combinatorial genetic analysis of five different electron conduits via creation of new markerless deletion strains and complementation vectors. Multiple conduit gene clusters appear to have overlapping roles, including two that have never been linked to metal reduction. Another recently described cluster (ExtABCD) was the only electron conduit essential during electrode reduction, a substrate of special importance to biotechnological applications of this organism. At least five gene clusters in the Geobacter sulfurreducens genome encode putative “electron conduits” implicated in electron transfer across the outer membrane, each containing a periplasmic multiheme c-type cytochrome, integral outer membrane anchor, and outer membrane redox lipoprotein(s). Markerless single-gene-cluster deletions and all possible multiple-deletion combinations were constructed and grown with soluble Fe(III) citrate, Fe(III) and Mn(IV) oxides, and graphite electrodes poised at +0.24 V and −0.1 V versus the standard hydrogen electrode (SHE). Different gene clusters were necessary for reduction of each electron acceptor. During metal oxide reduction, deletion of the previously described omcBC cluster caused defects, but deletion of additional components in an ΔomcBC background, such as extEFG, were needed to produce defects greater than 50% compared to findings with the wild type. Deletion of all five gene clusters abolished all metal reduction. During electrode reduction, only the ΔextABCD mutant had a severe growth defect at both redox potentials, while this mutation did not affect Fe(III) oxide, Mn(IV) oxide, or Fe(III) citrate reduction. Some mutants containing only one cluster were able to reduce particular terminal electron acceptors better than the wild type, suggesting routes for improvement by targeting specific electron transfer pathways. Transcriptomic comparisons between fumarate and electrode-based growth conditions showed all of these ext clusters to be constitutive, and transcriptional analysis of the triple-deletion strain containing only extABCD detected no significant changes in expression of genes encoding known redox proteins or pilus components. These genetic experiments reveal new outer membrane conduit complexes necessary for growth of G. sulfurreducens, depending on the available extracellular electron acceptor. IMPORTANCE Gram-negative metal-reducing bacteria utilize electron conduits, chains of redox proteins spanning the outer membrane, to transfer electrons to the extracellular surface. Only one pathway for electron transfer across the outer membrane of Geobacter sulfurreducens has been linked to Fe(III) reduction. However, G. sulfurreducens is able to respire a wide array of extracellular substrates. Here we present the first combinatorial genetic analysis of five different electron conduits via creation of new markerless deletion strains and complementation vectors. Multiple conduit gene clusters appear to have overlapping roles, including two that have never been linked to metal reduction. Another recently described cluster (ExtABCD) was the only electron conduit essential during electrode reduction, a substrate of special importance to biotechnological applications of this organism.
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28
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Ueki T, Nevin KP, Woodard TL, Aklujkar MA, Holmes DE, Lovley DR. Construction of a Geobacter Strain With Exceptional Growth on Cathodes. Front Microbiol 2018; 9:1512. [PMID: 30057572 PMCID: PMC6053493 DOI: 10.3389/fmicb.2018.01512] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 06/18/2018] [Indexed: 12/13/2022] Open
Abstract
Insoluble extracellular electron donors are important sources of energy for anaerobic respiration in biogeochemical cycling and in diverse practical applications. The previous lack of a genetically tractable model microorganism that could be grown to high densities under anaerobic conditions in pure culture with an insoluble extracellular electron donor has stymied efforts to better understand this form of respiration. We report here on the design of a strain of Geobacter sulfurreducens, designated strain ACL, which grows as thick (ca. 35 μm) confluent biofilms on graphite cathodes poised at -500 mV (versus Ag/AgCl) with fumarate as the electron acceptor. Sustained maximum current consumption rates were >0.8 A/m2, which is >10-fold higher than the current consumption of the wild-type strain. The improved function on the cathode was achieved by introducing genes for an ATP-dependent citrate lyase, completing the complement of enzymes needed for a reverse TCA cycle for the synthesis of biosynthetic precursors from carbon dioxide. Strain ACL provides an important model organism for elucidating the mechanisms for effective anaerobic growth with an insoluble extracellular electron donor and may offer unique possibilities as a chassis for the introduction of synthetic metabolic pathways for the production of commodities with electrons derived from electrodes.
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Affiliation(s)
- Toshiyuki Ueki
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States
| | - Kelly P Nevin
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States
| | - Trevor L Woodard
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States
| | - Muktak A Aklujkar
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States
| | - Dawn E Holmes
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States.,Department of Physical and Biological Sciences, Western New England University, Springfield, MA, United States
| | - Derek R Lovley
- Morrill Science Center IV, Department of Microbiology, University of Massachusetts, Amherst, MA, United States
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29
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Zacharoff LA, Morrone DJ, Bond DR. Geobacter sulfurreducens Extracellular Multiheme Cytochrome PgcA Facilitates Respiration to Fe(III) Oxides But Not Electrodes. Front Microbiol 2017; 8:2481. [PMID: 29312190 PMCID: PMC5732950 DOI: 10.3389/fmicb.2017.02481] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 11/29/2017] [Indexed: 11/13/2022] Open
Abstract
Extracellular cytochromes are hypothesized to facilitate the final steps of electron transfer between the outer membrane of the metal-reducing bacterium Geobacter sulfurreducens and solid-phase electron acceptors such as metal oxides and electrode surfaces during the course of respiration. The triheme c-type cytochrome PgcA exists in the extracellular space of G. sulfurreducens, and is one of many multiheme c-type cytochromes known to be loosely bound to the bacterial outer surface. Deletion of pgcA using a markerless method resulted in mutants unable to transfer electrons to Fe(III) and Mn(IV) oxides; yet the same mutants maintained the ability to respire to electrode surfaces and soluble Fe(III) citrate. When expressed and purified from Shewanella oneidensis, PgcA demonstrated a primarily alpha helical structure, three bound hemes, and was processed into a shorter 41 kDa form lacking the lipodomain. Purified PgcA bound Fe(III) oxides, but not magnetite, and when PgcA was added to cell suspensions of G. sulfurreducens, PgcA accelerated Fe(III) reduction similar to addition of FMN. Addition of soluble PgcA to ΔpgcA mutants also restored Fe(III) reduction. This report highlights a distinction between proteins involved in extracellular electron transfer to metal oxides and poised electrodes, and suggests a specific role for PgcA in facilitating electron transfer at mineral surfaces.
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Affiliation(s)
- Lori A Zacharoff
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN, United States
| | - Dana J Morrone
- St. Louis College of Pharmacy, St. Louis, MO, United States
| | - Daniel R Bond
- Department of Plant and Microbial Biology, University of Minnesota, Minneapolis, MN, United States.,BioTechnology Institute, University of Minnesota, Minneapolis, MN, United States
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30
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Genome Scale Mutational Analysis of Geobacter sulfurreducens Reveals Distinct Molecular Mechanisms for Respiration and Sensing of Poised Electrodes versus Fe(III) Oxides. J Bacteriol 2017; 199:JB.00340-17. [PMID: 28674067 PMCID: PMC5585712 DOI: 10.1128/jb.00340-17] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 06/23/2017] [Indexed: 12/11/2022] Open
Abstract
Geobacter sulfurreducens generates electrical current by coupling intracellular oxidation of organic acids to the reduction of proteins on the cell surface that are able to interface with electrodes. This ability is attributed to the bacterium's capacity to respire other extracellular electron acceptors that require contact, such as insoluble metal oxides. To directly investigate the genetic basis of electrode-based respiration, we constructed Geobacter sulfurreducens transposon-insertion sequencing (Tn-Seq) libraries for growth, with soluble fumarate or an electrode as the electron acceptor. Libraries with >33,000 unique insertions and an average of 9 insertions/kb allowed an assessment of each gene's fitness in a single experiment. Mutations in 1,214 different genomic features impaired growth with fumarate, and the significance of 270 genes unresolved by annotation due to the presence of one or more functional homologs was determined. Tn-Seq analysis of −0.1 V versus standard hydrogen electrode (SHE) electrode-grown cells identified mutations in a subset of genes encoding cytochromes, processing systems for proline-rich proteins, sensory networks, extracellular structures, polysaccharides, and metabolic enzymes that caused at least a 50% reduction in apparent growth rate. Scarless deletion mutants of select genes identified via Tn-Seq revealed a new putative porin-cytochrome conduit complex (extABCD) crucial for growth with electrodes, which was not required for Fe(III) oxide reduction. In addition, four mutants lacking components of a putative methyl-accepting chemotaxis–cyclic dinucleotide sensing network (esnABCD) were defective in electrode colonization but grew normally with Fe(III) oxides. These results suggest that G. sulfurreducens possesses distinct mechanisms for recognition, colonization, and reduction of electrodes compared to Fe(III) oxides. IMPORTANCE Since metal oxide electron acceptors are insoluble, one hypothesis is that cells sense and reduce metals using the same molecular mechanisms used to form biofilms on electrodes and produce electricity. However, by simultaneously comparing thousands of Geobacter sulfurreducens transposon mutants undergoing electrode-dependent respiration, we discovered new cytochromes and chemosensory proteins supporting growth with electrodes that are not required for metal respiration. This supports an emerging model where G. sulfurreducens recognizes surfaces and forms conductive biofilms using mechanisms distinct from those used for growth with metal oxides. These findings provide a possible explanation for studies that correlate electricity generation with syntrophic interspecies electron transfer by Geobacter and reveal many previously unrecognized targets for engineering this useful capability in other organisms.
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31
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Redox potential as a master variable controlling pathways of metal reduction by Geobacter sulfurreducens. ISME JOURNAL 2017; 11:741-752. [PMID: 28045456 PMCID: PMC5322298 DOI: 10.1038/ismej.2016.146] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 09/04/2016] [Accepted: 09/16/2016] [Indexed: 12/13/2022]
Abstract
Geobacter sulfurreducens uses at least two different pathways to transport electrons out of the inner membrane quinone pool before reducing acceptors beyond the outer membrane. When growing on electrodes poised at oxidizing potentials, the CbcL-dependent pathway operates at or below redox potentials of -0.10 V vs the standard hydrogen electrode, whereas the ImcH-dependent pathway operates only above this value. Here, we provide evidence that G. sulfurreducens also requires different electron transfer proteins for reduction of a wide range of Fe(III)- and Mn(IV)-(oxyhydr)oxides, and must transition from a high- to low-potential pathway during reduction of commonly studied soluble and insoluble metal electron acceptors. Freshly precipitated Fe(III)-(oxyhydr)oxides could not be reduced by mutants lacking the high-potential pathway. Aging these minerals by autoclaving did not change their powder X-ray diffraction pattern, but restored reduction by mutants lacking the high-potential pathway. Mutants lacking the low-potential, CbcL-dependent pathway had higher growth yields with both soluble and insoluble Fe(III). Together, these data suggest that the ImcH-dependent pathway exists to harvest additional energy when conditions permit, and CbcL switches on to allow respiration closer to thermodynamic equilibrium conditions. With evidence of multiple pathways within a single organism, the study of extracellular respiration should consider not only the crystal structure or solubility of a mineral electron acceptor, but rather the redox potential, as this variable determines the energetic reward affecting reduction rates, extents, and final microbial growth yields in the environment.
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32
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Ueki T, Nevin KP, Woodard TL, Lovley DR. Genetic switches and related tools for controlling gene expression and electrical outputs of Geobacter sulfurreducens. J Ind Microbiol Biotechnol 2016; 43:1561-1575. [PMID: 27659960 DOI: 10.1007/s10295-016-1836-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2016] [Accepted: 09/11/2016] [Indexed: 01/04/2023]
Abstract
Physiological studies and biotechnology applications of Geobacter species have been limited by a lack of genetic tools. Therefore, potential additional molecular strategies for controlling metabolism were explored. When the gene for citrate synthase, or acetyl-CoA transferase, was placed under the control of a LacI/IPTG regulator/inducer system, cells grew on acetate only in the presence of IPTG. The TetR/AT system could also be used to control citrate synthase gene expression and acetate metabolism. A strain that required IPTG for growth on D-lactate was constructed by placing the gene for D-lactate dehydrogenase under the control of the LacI/IPTG system. D-Lactate served as an inducer in a strain in which a D-lactate responsive promoter and transcription repressor were used to control citrate synthase expression. Iron- and potassium-responsive systems were successfully incorporated to regulate citrate synthase expression and growth on acetate. Linking the appropriate degradation tags on the citrate synthase protein made it possible to control acetate metabolism with either the endogenous ClpXP or exogenous Lon protease and tag system. The ability to control current output from Geobacter biofilms and the construction of an AND logic gate for acetate metabolism suggested that the tools developed may be applicable for biosensor and biocomputing applications.
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Affiliation(s)
- Toshiyuki Ueki
- Department of Microbiology, University of Massachusetts, Morrill Science Center IV North, 639 North Pleasant Street, Amherst, MA, 01003, USA.
| | - Kelly P Nevin
- Department of Microbiology, University of Massachusetts, Morrill Science Center IV North, 639 North Pleasant Street, Amherst, MA, 01003, USA
| | - Trevor L Woodard
- Department of Microbiology, University of Massachusetts, Morrill Science Center IV North, 639 North Pleasant Street, Amherst, MA, 01003, USA
| | - Derek R Lovley
- Department of Microbiology, University of Massachusetts, Morrill Science Center IV North, 639 North Pleasant Street, Amherst, MA, 01003, USA
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33
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Badalamenti JP, Summers ZM, Chan CH, Gralnick JA, Bond DR. Isolation and Genomic Characterization of 'Desulfuromonas soudanensis WTL', a Metal- and Electrode-Respiring Bacterium from Anoxic Deep Subsurface Brine. Front Microbiol 2016; 7:913. [PMID: 27445996 PMCID: PMC4914508 DOI: 10.3389/fmicb.2016.00913] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 05/27/2016] [Indexed: 11/25/2022] Open
Abstract
Reaching a depth of 713 m below the surface, the Soudan Underground Iron Mine (Soudan, MN, USA) transects a massive Archaean (2.7 Ga) banded iron formation, providing a remarkably accessible window into the terrestrial deep biosphere. Despite organic carbon limitation, metal-reducing microbial communities are present in potentially ancient anoxic brines continuously emanating from exploratory boreholes on Level 27. Using graphite electrodes deposited in situ as bait, we electrochemically enriched and isolated a novel halophilic iron-reducing Deltaproteobacterium, ‘Desulfuromonas soudanensis’ strain WTL, from an acetate-fed three-electrode bioreactor poised at +0.24 V (vs. standard hydrogen electrode). Cyclic voltammetry revealed that ‘D. soudanensis’ releases electrons at redox potentials approximately 100 mV more positive than the model freshwater surface isolate Geobacter sulfurreducens, suggesting that its extracellular respiration is tuned for higher potential electron acceptors. ‘D. soudanensis’ contains a 3,958,620-bp circular genome, assembled to completion using single-molecule real-time (SMRT) sequencing reads, which encodes a complete TCA cycle, 38 putative multiheme c-type cytochromes, one of which contains 69 heme-binding motifs, and a LuxI/LuxR quorum sensing cassette that produces an unidentified N-acyl homoserine lactone. Another cytochrome is predicted to lie within a putative prophage, suggesting that horizontal gene transfer plays a role in respiratory flexibility among metal reducers. Isolation of ‘D. soudanensis’ underscores the utility of electrode-based approaches for enriching rare metal reducers from a wide range of habitats.
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Affiliation(s)
| | - Zarath M Summers
- BioTechnology Institute, University of Minnesota - Twin Cities, Saint Paul MN, USA
| | - Chi Ho Chan
- BioTechnology Institute, University of Minnesota - Twin Cities, Saint Paul MN, USA
| | - Jeffrey A Gralnick
- BioTechnology Institute, University of Minnesota - Twin Cities, Saint PaulMN, USA; Department of Microbiology, University of Minnesota - Twin Cities, MinneapolisMN, USA
| | - Daniel R Bond
- BioTechnology Institute, University of Minnesota - Twin Cities, Saint PaulMN, USA; Department of Microbiology, University of Minnesota - Twin Cities, MinneapolisMN, USA
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