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Pandey CB, Kumar U, Kaviraj M, Minick KJ, Mishra AK, Singh JS. DNRA: A short-circuit in biological N-cycling to conserve nitrogen in terrestrial ecosystems. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 738:139710. [PMID: 32544704 DOI: 10.1016/j.scitotenv.2020.139710] [Citation(s) in RCA: 109] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 05/21/2020] [Accepted: 05/23/2020] [Indexed: 06/11/2023]
Abstract
This paper reviews dissimilatory nitrate reduction to ammonium (DNRA) in soils - a newly appreciated pathway of nitrogen (N) cycling in the terrestrial ecosystems. The reduction of NO3- occurs in two steps; in the first step, NO3- is reduced to NO2-; and in the second, unlike denitrification, NO2- is reduced to NH4+ without intermediates. There are two sets of NO3-/NO2- reductase enzymes, i.e., Nap/Nrf and Nar/Nir; the former occurs on the periplasmic-membrane and energy conservation is respiratory via electron-transport-chain, whereas the latter is cytoplasmic and energy conservation is both respiratory and fermentative (Nir, substrate-phosphorylation). Since, Nir catalyzes both assimilatory- and dissimilatory-nitrate reduction, the nrfA gene, which transcribes the NrfA protein, is treated as a molecular-marker of DNRA; and a high nrfA/nosZ (N2O-reductase) ratio favours DNRA. Recently, several crystal structures of NrfA have been presumed to producee N2O as a byproduct of DNRA via the NO (nitric-oxide) pathway. Meta-analyses of about 200 publications have revealed that DNRA is regulated by oxidation state of soils and sediments, carbon (C)/N and NO2-/NO3- ratio, and concentrations of ferrous iron (Fe2+) and sulfide (S2-). Under low-redox conditions, a high C/NO3- ratio selects for DNRA while a low ratio selects for denitrification. When the proportion of both C and NO3- are equal, the NO2-/NO3- ratio modulates partitioning of NO3-, and a high NO2-/NO3- ratio favours DNRA. A high S2-/NO3- ratio also promotes DNRA in coastal-ecosystems and saline sediments. Soil pH, temperature, and fine soil particles are other factors known to influence DNRA. Since, DNRA reduces NO3- to NH4+, it is essential for protecting NO3- from leaching and gaseous (N2O) losses and enriches soils with readily available NH4+-N to primary producers and heterotrophic microorganisms. Therefore, DNRA may be treated as a tool to reduce ground-water NO3- pollution, enhance soil health and improve environmental quality.
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Affiliation(s)
- C B Pandey
- ICAR-Central Arid Zone Research Institute, Jodhpur 342003, Rajasthan, India.
| | - Upendra Kumar
- ICAR-National Rice Research Institute, Cuttack 753006, Odisha, India.
| | - Megha Kaviraj
- ICAR-National Rice Research Institute, Cuttack 753006, Odisha, India
| | - K J Minick
- Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695, USA
| | - A K Mishra
- International Rice Research Institute, New Delhi 110012, India
| | - J S Singh
- Ecosystem Analysis Lab, Centre of Advanced Study in Botany, Banaras Hindu University (BHU), Varanasi 221005, India
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2
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Bacterial nitrous oxide respiration: electron transport chains and copper transfer reactions. Adv Microb Physiol 2019; 75:137-175. [PMID: 31655736 DOI: 10.1016/bs.ampbs.2019.07.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Biologically catalyzed nitrous oxide (N2O, laughing gas) reduction to dinitrogen gas (N2) is a desirable process in the light of ever-increasing atmospheric concentrations of this important greenhouse gas and ozone depleting substance. A diverse range of bacterial species produce the copper cluster-containing enzyme N2O reductase (NosZ), which is the only known enzyme that converts N2O to N2. Based on phylogenetic analyses, NosZ enzymes have been classified into clade I or clade II and it has turned out that this differentiation is also applicable to nos gene clusters (NGCs) and some physiological traits of the corresponding microbial cells. The NosZ enzyme is the terminal reductase of anaerobic N2O respiration, in which electrons derived from a donor substrate are transferred to NosZ by means of an electron transport chain (ETC) that conserves energy through proton motive force generation. This chapter presents models of the ETCs involved in clade I and clade II N2O respiration as well as of the respective NosZ maturation and maintenance processes. Despite differences in NGCs and growth yields of N2O-respiring microorganisms, the deduced bioenergetic framework in clade I and clade II N2O respiration is assumed to be equivalent. In both cases proton motive quinol oxidation by N2O is thought to be catalyzed by the Q cycle mechanism of a membrane-bound Rieske/cytochrome bc complex. However, clade I and clade II organisms are expected to differ significantly in terms of auxiliary electron transport processes as well as NosZ active site maintenance and repair.
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Türkowsky D, Jehmlich N, Diekert G, Adrian L, von Bergen M, Goris T. An integrative overview of genomic, transcriptomic and proteomic analyses in organohalide respiration research. FEMS Microbiol Ecol 2019; 94:4830072. [PMID: 29390082 DOI: 10.1093/femsec/fiy013] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Accepted: 01/24/2018] [Indexed: 02/06/2023] Open
Abstract
Organohalide respiration (OHR) is a crucial process in the global halogen cycle and of interest for bioremediation. However, investigations on OHR are hampered by the restricted genetic accessibility and the poor growth yields of many organohalide-respiring bacteria (OHRB). Therefore, genomics, transcriptomics and proteomics are often used to investigate OHRB. In general, these gene expression studies are more useful when the data of the different 'omics' approaches are integrated and compared among a wide range of cultivation conditions and ideally involve several closely related OHRB. Despite the availability of a couple of proteomic and transcriptomic datasets dealing with OHRB, such approaches are currently not covered in reviews. Therefore, we here present an integrative and comparative overview of omics studies performed with the OHRB Sulfurospirillum multivorans, Dehalococcoides mccartyi, Desulfitobacterium spp. and Dehalobacter restrictus. Genes, transcripts, proteins and the regulatory and biochemical processes involved in OHR are discussed, and a comprehensive view on the unusual metabolism of D. mccartyi, which is one of the few bacteria possibly using a quinone-independent respiratory chain, is provided. Several 'omics'-derived theories on OHRB, e.g. the organohalide-respiratory chain, hydrogen metabolism, corrinoid biosynthesis or one-carbon metabolism are critically discussed on the basis of this integrative approach.
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Affiliation(s)
- Dominique Türkowsky
- Department of Molecular Systems Biology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Nico Jehmlich
- Department of Molecular Systems Biology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany
| | - Gabriele Diekert
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Philosophenweg 12, 07743 Jena, Germany
| | - Lorenz Adrian
- Department of Isotope Biogeochemistry, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany.,Chair of Geobiotechnology, Technische Universität Berlin, Ackerstraße 76, 13355 Berlin
| | - Martin von Bergen
- Department of Molecular Systems Biology, Helmholtz Centre for Environmental Research - UFZ, Permoserstraße 15, 04318 Leipzig, Germany.,Institute of Biochemistry, Faculty of Life Sciences, University of Leipzig, Brüderstraße 34, Germany
| | - Tobias Goris
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Philosophenweg 12, 07743 Jena, Germany
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Taylor AJ, Kelly DJ. The function, biogenesis and regulation of the electron transport chains in Campylobacter jejuni: New insights into the bioenergetics of a major food-borne pathogen. Adv Microb Physiol 2019; 74:239-329. [PMID: 31126532 DOI: 10.1016/bs.ampbs.2019.02.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Campylobacter jejuni is a zoonotic Epsilonproteobacterium that grows in the gastrointestinal tract of birds and mammals, and is the most frequent cause of food-borne bacterial gastroenteritis worldwide. As an oxygen-sensitive microaerophile, C. jejuni has to survive high environmental oxygen tensions, adapt to oxygen limitation in the host intestine and resist host oxidative attack. Despite its small genome size, C. jejuni is a versatile and metabolically active pathogen, with a complex and highly branched set of respiratory chains allowing the use of a wide range of electron donors and alternative electron acceptors in addition to oxygen, including fumarate, nitrate, nitrite, tetrathionate and N- or S-oxides. Several novel enzymes participate in these electron transport chains, including a tungsten containing formate dehydrogenase, a Complex I that uses flavodoxin and not NADH, a periplasmic facing fumarate reductase and a cytochrome c tetrathionate reductase. This review presents an updated description of the composition and bioenergetics of these various respiratory chains as they are currently understood, including recent work that gives new insights into energy conservation during electron transport to various alternative electron acceptors. The regulation of synthesis and assembly of the electron transport chains is also discussed. A deeper appreciation of the unique features of the respiratory systems of C. jejuni may be helpful in informing strategies to control this important pathogen.
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Affiliation(s)
- Aidan J Taylor
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
| | - David J Kelly
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Western Bank, Sheffield S10 2TN, UK
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5
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Garg N, Taylor AJ, Kelly DJ. Bacterial periplasmic nitrate and trimethylamine-N-oxide respiration coupled to menaquinol-cytochrome c reductase (Qcr): Implications for electrogenic reduction of alternative electron acceptors. Sci Rep 2018; 8:15478. [PMID: 30341307 PMCID: PMC6195509 DOI: 10.1038/s41598-018-33857-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Accepted: 10/08/2018] [Indexed: 12/14/2022] Open
Abstract
The periplasmic reduction of the electron acceptors nitrate (Em +420 mV) and trimethylamine-N-oxide (TMAO; Em +130 mV) by Nap and Tor reductases is widespread in Gram-negative bacteria and is usually considered to be driven by non-energy conserving quinol dehydrogenases. The Epsilonproteobacterium Campylobacter jejuni can grow by nitrate and TMAO respiration and it has previously been assumed that these alternative pathways of electron transport are independent of the proton-motive menaquinol-cytochrome c reductase complex (QcrABC) that functions in oxygen-linked respiration. Here, we show that a qcrABC deletion mutant is completely deficient in oxygen-limited growth on both nitrate and TMAO and is unable to reduce these oxidants with physiological electron donors. As expected, the mutant grows normally on fumarate under oxygen-limited conditions. Thus, the periplasmic Nap and Tor reductases receive their electrons via QcrABC in C. jejuni, explaining the general absence of NapC and TorC quinol dehydrogenases in Epsilonproteobacteria. Moreover, the specific use of menaquinol (Em -75 mV) coupled with a Qcr complex to drive reduction of nitrate or TMAO against the proton-motive force allows the process to be electrogenic with a H+/2e- ratio of 2. The results have general implications for the role of Qcr complexes in bacterial oxygen-independent respiration and growth.
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Affiliation(s)
- Nitanshu Garg
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - Aidan J Taylor
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK
| | - David J Kelly
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield, S10 2TN, UK.
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Buttet GF, Willemin MS, Hamelin R, Rupakula A, Maillard J. The Membrane-Bound C Subunit of Reductive Dehalogenases: Topology Analysis and Reconstitution of the FMN-Binding Domain of PceC. Front Microbiol 2018; 9:755. [PMID: 29740408 PMCID: PMC5928378 DOI: 10.3389/fmicb.2018.00755] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 04/04/2018] [Indexed: 12/15/2022] Open
Abstract
Organohalide respiration (OHR) is the energy metabolism of anaerobic bacteria able to use halogenated organic compounds as terminal electron acceptors. While the terminal enzymes in OHR, so-called reductive dehalogenases, are well-characterized, the identity of proteins potentially involved in electron transfer to the terminal enzymes remains elusive. Among the accessory genes identified in OHR gene clusters, the C subunit (rdhC) could well code for the missing redox protein between the quinol pool and the reductive dehalogenase, although it was initially proposed to act as transcriptional regulator. RdhC sequences are characterized by the presence of multiple transmembrane segments, a flavin mononucleotide (FMN) binding motif and two conserved CX3CP motifs. Based on these features, we propose a curated selection of RdhC proteins identified in general sequence databases. Beside the Firmicutes from which RdhC sequences were initially identified, the identified sequences belong to three additional phyla, the Chloroflexi, the Proteobacteria, and the Bacteriodetes. The diversity of RdhC sequences mostly respects the phylogenetic distribution, suggesting that rdhC genes emerged relatively early in the evolution of the OHR metabolism. PceC, the C subunit of the tetrachloroethene (PCE) reductive dehalogenase is encoded by the conserved pceABCT gene cluster identified in Dehalobacter restrictus PER-K23 and in several strains of Desulfitobacterium hafniense. Surfaceome analysis of D. restrictus cells confirmed the predicted topology of the FMN-binding domain (FBD) of PceC that is the exocytoplasmic face of the membrane. Starting from inclusion bodies of a recombinant FBD protein, strategies for successful assembly of the FMN cofactor and refolding were achieved with the use of the flavin-trafficking protein from D. hafniense TCE1. Mass spectrometry analysis and site-directed mutagenesis of rFBD revealed that threonine-168 of PceC is binding FMN covalently. Our results suggest that PceC, and more generally RdhC proteins, may play a role in electron transfer in the metabolism of OHR.
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Affiliation(s)
- Géraldine F Buttet
- Laboratory for Environmental Biotechnology, Institute for Environmental Engineering, Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland
| | - Mathilde S Willemin
- Laboratory for Environmental Biotechnology, Institute for Environmental Engineering, Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland
| | - Romain Hamelin
- Protein Core Facility, Faculty of Life Sciences, Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland
| | - Aamani Rupakula
- Laboratory for Environmental Biotechnology, Institute for Environmental Engineering, Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland
| | - Julien Maillard
- Laboratory for Environmental Biotechnology, Institute for Environmental Engineering, Swiss Federal Institute of Technology in Lausanne, Lausanne, Switzerland
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7
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Schubert T, Adrian L, Sawers RG, Diekert G. Organohalide respiratory chains: composition, topology and key enzymes. FEMS Microbiol Ecol 2018; 94:4923014. [DOI: 10.1093/femsec/fiy035] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 02/28/2018] [Indexed: 02/07/2023] Open
Affiliation(s)
- Torsten Schubert
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Philosophenweg 12, D-07743 Jena, Germany
| | - Lorenz Adrian
- Department Isotope Biogeochemistry, Helmholtz Centre for Environmental Research-UFZ, Permoserstraße 15, D-04318 Leipzig, Germany
- Department of Geobiotechnology, Technische Universität Berlin, Ackerstraße 74, D-13355 Berlin, Germany
| | - R Gary Sawers
- Institute of Biology/Microbiology, Martin Luther University Halle-Wittenberg, Kurt-Mothes-Straße 3, D-06120 Halle (Saale), Germany
| | - Gabriele Diekert
- Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Philosophenweg 12, D-07743 Jena, Germany
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8
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Hein S, Witt S, Simon J. Clade II nitrous oxide respiration of Wolinella succinogenes depends on the NosG, -C1, -C2, -H electron transport module, NosB and a Rieske/cytochrome bc complex. Environ Microbiol 2017; 19:4913-4925. [PMID: 28925551 DOI: 10.1111/1462-2920.13935] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Revised: 09/14/2017] [Accepted: 09/16/2017] [Indexed: 01/20/2023]
Abstract
Microbial reduction of nitrous oxide (N2 O) is an environmentally significant process in the biogeochemical nitrogen cycle. However, it has been recognized only recently that the gene encoding N2 O reductase (nosZ) is organized in varying genetic contexts, thereby defining clade I (or 'typical') and clade II (or 'atypical') N2 O reductases and nos gene clusters. This study addresses the enzymology of the clade II Nos system from Wolinella succinogenes, a nitrate-ammonifying and N2 O-respiring Epsilonproteobacterium that contains a cytochrome c N2 O reductase (cNosZ). The characterization of single non-polar nos gene deletion mutants demonstrated that the NosG, -C1, -C2, -H and -B proteins were essential for N2 O respiration. Moreover, cells of a W. succinogenes mutant lacking a putative menaquinol-oxidizing Rieske/cytochrome bc complex (QcrABC) were found to be incapable of N2 O (and also nitrate) respiration. Proton motive menaquinol oxidation by N2 O is suggested, supported by the finding that the molar yield for W. succinogenes cells grown by N2 O respiration using formate as electron donor exceeded that of fumarate respiration by about 30%. The results demand revision of the electron transport chain model of clade II N2 O respiration and challenge the assumption that NosGH(NapGH)-type iron-sulfur proteins are menaquinol-reactive.
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Affiliation(s)
- Sascha Hein
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
| | - Samantha Witt
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
| | - Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287 Darmstadt, Germany
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9
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Bhowmik A, Cloutier M, Ball E, Bruns MA. Underexplored microbial metabolisms for enhanced nutrient recycling in agricultural soils. AIMS Microbiol 2017; 3:826-845. [PMID: 31294192 PMCID: PMC6604955 DOI: 10.3934/microbiol.2017.4.826] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Accepted: 09/21/2017] [Indexed: 01/03/2023] Open
Abstract
Worldwide, arable soils have been degraded through erosion and exhaustive cultivation, and substantial proportions of fertilizer nutrients are not taken up by crops. A central challenge in agriculture is to understand how soils and resident microbial communities can be managed to deliver nutrients to crops more efficiently with minimal losses to the environment. Throughout much of the twentieth century, intensive farming has caused substantial loss of organic matter and soil biological function. Today, more farmers recognize the importance of protecting soils and restoring organic matter through reduced tillage, diversified crop rotation, cover cropping, and increased organic amendments. Such management practices are expected to foster soil conditions more similar to those of undisturbed, native plant-soil systems by restoring soil biophysical integrity and re-establishing plant-microbe interactions that retain and recycle nutrients. Soil conditions which could contribute to desirable shifts in microbial metabolic processes include lower redox potentials, more diverse biogeochemical gradients, higher concentrations of labile carbon, and enrichment of carbon dioxide (CO2) and hydrogen gas (H2) in soil pores. This paper reviews recent literature on generalized and specific microbial processes that could become more operational once soils are no longer subjected to intensive tillage and organic matter depletion. These processes include heterotrophic assimilation of CO2; utilization of H2 as electron donor or reactant; and more diversified nitrogen uptake and dissimilation pathways. Despite knowledge of these processes occurring in laboratory studies, they have received little attention for their potential to affect nutrient and energy flows in soils. This paper explores how soil microbial processes could contribute to in situ nutrient retention, recycling, and crop uptake in agricultural soils managed for improved biological function.
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Affiliation(s)
- Arnab Bhowmik
- Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, USA
| | - Mara Cloutier
- Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, USA
- Dual-Title Graduate Program in Biogeochemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - Emily Ball
- Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, USA
| | - Mary Ann Bruns
- Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, PA 16802, USA
- Dual-Title Graduate Program in Biogeochemistry, The Pennsylvania State University, University Park, PA 16802, USA
- Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, PA 16802, USA
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10
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Tooke FJ, Babot M, Chandra G, Buchanan G, Palmer T. A unifying mechanism for the biogenesis of membrane proteins co-operatively integrated by the Sec and Tat pathways. eLife 2017; 6. [PMID: 28513434 PMCID: PMC5449189 DOI: 10.7554/elife.26577] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 05/15/2017] [Indexed: 11/13/2022] Open
Abstract
The majority of multi-spanning membrane proteins are co-translationally inserted into the bilayer by the Sec pathway. An important subset of membrane proteins have globular, cofactor-containing extracytoplasmic domains requiring the dual action of the co-translational Sec and post-translational Tat pathways for integration. Here, we identify further unexplored families of membrane proteins that are dual Sec-Tat-targeted. We establish that a predicted heme-molybdenum cofactor-containing protein, and a complex polyferredoxin, each require the concerted action of two translocases for their assembly. We determine that the mechanism of handover from Sec to Tat pathway requires the relatively low hydrophobicity of the Tat-dependent transmembrane domain. This, coupled with the presence of C-terminal positive charges, results in abortive insertion of this transmembrane domain by the Sec pathway and its subsequent release at the cytoplasmic side of the membrane. Together, our data points to a simple unifying mechanism governing the assembly of dual targeted membrane proteins.
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Affiliation(s)
- Fiona J Tooke
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Marion Babot
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Govind Chandra
- Department of Molecular Microbiology, John Innes Centre, Norwich, United Kingdom
| | - Grant Buchanan
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Tracy Palmer
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
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11
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Haase D, Hermann B, Einsle O, Simon J. Epsilonproteobacterial hydroxylamine oxidoreductase (
ε
Hao): characterization of a ‘missing link’ in the multihaem cytochrome
c
family. Mol Microbiol 2017; 105:127-138. [DOI: 10.1111/mmi.13690] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Doreen Haase
- Microbial Energy Conversion and Biotechnology, Department of BiologyTechnische Universität DarmstadtSchnittspahnstraße 1064287Darmstadt Germany
| | - Bianca Hermann
- Lehrstuhl Biochemie, Institut für BiochemieAlbert‐Ludwigs‐Universität FreiburgAlbertstrasse 2179104Freiburg Germany
| | - Oliver Einsle
- Lehrstuhl Biochemie, Institut für BiochemieAlbert‐Ludwigs‐Universität FreiburgAlbertstrasse 2179104Freiburg Germany
| | - Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of BiologyTechnische Universität DarmstadtSchnittspahnstraße 1064287Darmstadt Germany
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12
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Torres M, Simon J, Rowley G, Bedmar E, Richardson D, Gates A, Delgado M. Nitrous Oxide Metabolism in Nitrate-Reducing Bacteria: Physiology and Regulatory Mechanisms. Adv Microb Physiol 2016; 68:353-432. [PMID: 27134026 DOI: 10.1016/bs.ampbs.2016.02.007] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Nitrous oxide (N2O) is an important greenhouse gas (GHG) with substantial global warming potential and also contributes to ozone depletion through photochemical nitric oxide (NO) production in the stratosphere. The negative effects of N2O on climate and stratospheric ozone make N2O mitigation an international challenge. More than 60% of global N2O emissions are emitted from agricultural soils mainly due to the application of synthetic nitrogen-containing fertilizers. Thus, mitigation strategies must be developed which increase (or at least do not negatively impact) on agricultural efficiency whilst decrease the levels of N2O released. This aim is particularly important in the context of the ever expanding population and subsequent increased burden on the food chain. More than two-thirds of N2O emissions from soils can be attributed to bacterial and fungal denitrification and nitrification processes. In ammonia-oxidizing bacteria, N2O is formed through the oxidation of hydroxylamine to nitrite. In denitrifiers, nitrate is reduced to N2 via nitrite, NO and N2O production. In addition to denitrification, respiratory nitrate ammonification (also termed dissimilatory nitrate reduction to ammonium) is another important nitrate-reducing mechanism in soil, responsible for the loss of nitrate and production of N2O from reduction of NO that is formed as a by-product of the reduction process. This review will synthesize our current understanding of the environmental, regulatory and biochemical control of N2O emissions by nitrate-reducing bacteria and point to new solutions for agricultural GHG mitigation.
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13
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Arshad A, Speth DR, de Graaf RM, Op den Camp HJM, Jetten MSM, Welte CU. A Metagenomics-Based Metabolic Model of Nitrate-Dependent Anaerobic Oxidation of Methane by Methanoperedens-Like Archaea. Front Microbiol 2015; 6:1423. [PMID: 26733968 PMCID: PMC4683180 DOI: 10.3389/fmicb.2015.01423] [Citation(s) in RCA: 120] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 11/30/2015] [Indexed: 11/22/2022] Open
Abstract
Methane oxidation is an important process to mitigate the emission of the greenhouse gas methane and further exacerbating of climate forcing. Both aerobic and anaerobic microorganisms have been reported to catalyze methane oxidation with only a few possible electron acceptors. Recently, new microorganisms were identified that could couple the oxidation of methane to nitrate or nitrite reduction. Here we investigated such an enrichment culture at the (meta) genomic level to establish a metabolic model of nitrate-driven anaerobic oxidation of methane (nitrate-AOM). Nitrate-AOM is catalyzed by an archaeon closely related to (reverse) methanogens that belongs to the ANME-2d clade, tentatively named Methanoperedens nitroreducens. Methane may be activated by methyl-CoM reductase and subsequently undergo full oxidation to carbon dioxide via reverse methanogenesis. All enzymes of this pathway were present and expressed in the investigated culture. The genome of the archaeal enrichment culture encoded a variety of enzymes involved in an electron transport chain similar to those found in Methanosarcina species with additional features not previously found in methane-converting archaea. Nitrate reduction to nitrite seems to be located in the pseudoperiplasm and may be catalyzed by an unusual Nar-like protein complex. A small part of the resulting nitrite is reduced to ammonium which may be catalyzed by a Nrf-type nitrite reductase. One of the key questions is how electrons from cytoplasmically located reverse methanogenesis reach the nitrate reductase in the pseudoperiplasm. Electron transport in M. nitroreducens probably involves cofactor F420 in the cytoplasm, quinones in the cytoplasmic membrane and cytochrome c in the pseudoperiplasm. The membrane-bound electron transport chain includes F420H2 dehydrogenase and an unusual Rieske/cytochrome b complex. Based on genome and transcriptome studies a tentative model of how central energy metabolism of nitrate-AOM could work is presented and discussed.
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Affiliation(s)
- Arslan Arshad
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
| | - Daan R Speth
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
| | - Rob M de Graaf
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
| | - Huub J M Op den Camp
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
| | - Mike S M Jetten
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
| | - Cornelia U Welte
- Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Netherlands
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Kern M, Simon J. Three transcription regulators of the Nss family mediate the adaptive response induced by nitrate, nitric oxide or nitrous oxide in Wolinella succinogenes. Environ Microbiol 2015; 18:2899-912. [PMID: 26395430 DOI: 10.1111/1462-2920.13060] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 09/16/2015] [Indexed: 12/30/2022]
Abstract
Sensing potential nitrogen-containing respiratory substrates such as nitrate, nitrite, hydroxylamine, nitric oxide (NO) or nitrous oxide (N2 O) in the environment and subsequent upregulation of corresponding catabolic enzymes is essential for many microbial cells. The molecular mechanisms of such adaptive responses are, however, highly diverse in different species. Here, induction of periplasmic nitrate reductase (Nap), cytochrome c nitrite reductase (Nrf) and cytochrome c N2 O reductase (cNos) was investigated in cells of the Epsilonproteobacterium Wolinella succinogenes grown either by fumarate, nitrate or N2 O respiration. Furthermore, fumarate respiration in the presence of various nitrogen compounds or NO-releasing chemicals was examined. Upregulation of each of the Nap, Nrf and cNos enzyme systems was found in response to the presence of nitrate, NO-releasers or N2 O, and the cells were shown to employ three transcription regulators of the Crp-Fnr superfamily (homologues of Campylobacter jejuni NssR), designated NssA, NssB and NssC, to mediate the upregulation of Nap, Nrf and cNos. Analysis of single nss mutants revealed that NssA controls production of the Nap and Nrf systems in fumarate-grown cells, while NssB was required to induce the Nap, Nrf and cNos systems specifically in response to NO-generators. NssC was indispensable for cNos production under any tested condition. The data indicate dedicated signal transduction routes responsive to nitrate, NO and N2 O and imply the presence of an N2 O-sensing mechanism.
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Affiliation(s)
- Melanie Kern
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287, Darmstadt, Germany
| | - Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstraße 10, 64287, Darmstadt, Germany.
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15
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Proteomics of the organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans adapted to tetrachloroethene and other energy substrates. Sci Rep 2015; 5:13794. [PMID: 26387727 PMCID: PMC4585668 DOI: 10.1038/srep13794] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 08/05/2015] [Indexed: 12/15/2022] Open
Abstract
Organohalide respiration is an environmentally important but poorly characterized type of anaerobic respiration. We compared the global proteome of the versatile organohalide-respiring Epsilonproteobacterium Sulfurospirillum multivorans grown with different electron acceptors (fumarate, nitrate, or tetrachloroethene [PCE]). The most significant differences in protein abundance were found for gene products of the organohalide respiration region. This genomic region encodes the corrinoid and FeS cluster containing PCE reductive dehalogenase PceA and other proteins putatively involved in PCE metabolism such as those involved in corrinoid biosynthesis. The latter gene products as well as PceA and a putative quinol dehydrogenase were almost exclusively detected in cells grown with PCE. This finding suggests an electron flow from the electron donor such as formate or pyruvate via the quinone pool and a quinol dehydrogenase to PceA and the terminal electron acceptor PCE. Two putative accessory proteins, an IscU-like protein and a peroxidase-like protein, were detected with PCE only and might be involved in PceA maturation. The proteome of cells grown with pyruvate instead of formate as electron donor indicates a route of electrons from reduced ferredoxin via an Epsilonproteobacterial complex I and the quinone pool to PCE.
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16
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Visser M, Pieterse MM, Pinkse MWH, Nijsse B, Verhaert PDEM, de Vos WM, Schaap PJ, Stams AJM. Unravelling the one-carbon metabolism of the acetogen Sporomusa strain An4 by genome and proteome analysis. Environ Microbiol 2015; 18:2843-55. [PMID: 26147498 DOI: 10.1111/1462-2920.12973] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Revised: 06/19/2015] [Accepted: 06/26/2015] [Indexed: 01/06/2023]
Abstract
The Sporomusa genus comprises anaerobic spore-forming acetogenic bacteria that stain Gram-negative. Sporomusa species typically grow with one-carbon substrates and N-methylated compounds. In the degradation of these compounds methyltransferases are involved. In addition, Sporomusa species can grow autotrophically with H2 and CO2 , and use a variety of sugars for acetogenic growth. Here we describe a genome analysis of Sporomusa strain An4 and a proteome analysis of cells grown under five different conditions. Comparison of the genomes of Sporomusa strain An4 and Sporomusa ovata strain H1 indicated that An4 is a S. ovata strain. Proteome analysis showed a high abundance of several methyltransferases, predominantly trimethylamine methyltransferases, during growth with betaine, whereas trimethylamine is one of the main end-products of betaine degradation. In methanol degradation methyltransferases are also involved. In methanol-utilizing methanogens, two methyltransferases catalyse methanol conversion, methyltransferase 1 composed of subunits MtaB and MtaC and methyltransferase 2, also called MtaA. The two methyltransferase 1 subunits MtaB and MtaC were highly abundant when strain An4 was grown with methanol. However, instead of MtaA a methyltetrahydrofolate methyltransferase was synthesized. We propose a novel methanol degradation pathway in Sporomusa strain An4 that uses a methyltetrahydrofolate methyltransferase instead of MtaA.
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Affiliation(s)
- Michael Visser
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.
| | - Mervin M Pieterse
- Department of Biotechnology, Technische Universiteit Delft, Julianalaan 67, 2628 BC, Delft, The Netherlands.,Netherlands Proteomics Centre, Julianalaan 67, 2628 BC, Delft, The Netherlands
| | - Martijn W H Pinkse
- Department of Biotechnology, Technische Universiteit Delft, Julianalaan 67, 2628 BC, Delft, The Netherlands.,Netherlands Proteomics Centre, Julianalaan 67, 2628 BC, Delft, The Netherlands
| | - Bart Nijsse
- Laboratory of Systems and Synthetic Biology, Wageningen University, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Peter D E M Verhaert
- Department of Biotechnology, Technische Universiteit Delft, Julianalaan 67, 2628 BC, Delft, The Netherlands.,Netherlands Proteomics Centre, Julianalaan 67, 2628 BC, Delft, The Netherlands
| | - Willem M de Vos
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.,Department of Veterinary Biosciences, Helsinki University, Helsinki, Finland.,Department of Bacteriology and Immunology, Helsinki University, Helsinki, Finland
| | - Peter J Schaap
- Laboratory of Systems and Synthetic Biology, Wageningen University, Stippeneng 4, 6708 WE, Wageningen, The Netherlands
| | - Alfons J M Stams
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708 WE, Wageningen, The Netherlands.,CEB-Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal
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17
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Assessment of the Carbon Monoxide Metabolism of the Hyperthermophilic Sulfate-Reducing Archaeon Archaeoglobus fulgidus VC-16 by Comparative Transcriptome Analyses. ARCHAEA-AN INTERNATIONAL MICROBIOLOGICAL JOURNAL 2015; 2015:235384. [PMID: 26345487 PMCID: PMC4543118 DOI: 10.1155/2015/235384] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 06/09/2015] [Accepted: 06/14/2015] [Indexed: 11/23/2022]
Abstract
The hyperthermophilic, sulfate-reducing archaeon, Archaeoglobus fulgidus, utilizes CO as an energy source and it is resistant to the toxic effects of high CO concentrations. Herein, transcription profiles were obtained from A. fulgidus during growth with CO and sulfate or thiosulfate, or without an electron acceptor. This provided a basis for a model of the CO metabolism of A. fulgidus. The model suggests proton translocation by “Mitchell-type” loops facilitated by Fqo catalyzing a Fdred:menaquinone oxidoreductase reaction, as the major mode of energy conservation, rather than formate or H2 cycling during respiratory growth. The bifunctional CODH (cdhAB-2) is predicted to play an ubiquitous role in the metabolism of CO, and a novel nitrate reductase-associated respiratory complex was induced specifically in the presence of sulfate. A potential role of this complex in relation to Fdred and APS reduction is discussed. Multiple membrane-bound heterodisulfide reductase (DsrMK) could promote both energy-conserving and non-energy-conserving menaquinol oxidation. Finally, the FqoF subunit may catalyze a Fdred:F420 oxidoreductase reaction. In the absence of electron acceptor, downregulation of F420H2 dependent steps of the acetyl-CoA pathway is linked to transient formate generation. Overall, carboxidotrophic growth seems as an intrinsic capacity of A. fulgidus with little need for novel resistance or respiratory complexes.
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A Post-Genomic View of the Ecophysiology, Catabolism and Biotechnological Relevance of Sulphate-Reducing Prokaryotes. Adv Microb Physiol 2015. [PMID: 26210106 DOI: 10.1016/bs.ampbs.2015.05.002] [Citation(s) in RCA: 174] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Dissimilatory sulphate reduction is the unifying and defining trait of sulphate-reducing prokaryotes (SRP). In their predominant habitats, sulphate-rich marine sediments, SRP have long been recognized to be major players in the carbon and sulphur cycles. Other, more recently appreciated, ecophysiological roles include activity in the deep biosphere, symbiotic relations, syntrophic associations, human microbiome/health and long-distance electron transfer. SRP include a high diversity of organisms, with large nutritional versatility and broad metabolic capacities, including anaerobic degradation of aromatic compounds and hydrocarbons. Elucidation of novel catabolic capacities as well as progress in the understanding of metabolic and regulatory networks, energy metabolism, evolutionary processes and adaptation to changing environmental conditions has greatly benefited from genomics, functional OMICS approaches and advances in genetic accessibility and biochemical studies. Important biotechnological roles of SRP range from (i) wastewater and off gas treatment, (ii) bioremediation of metals and hydrocarbons and (iii) bioelectrochemistry, to undesired impacts such as (iv) souring in oil reservoirs and other environments, and (v) corrosion of iron and concrete. Here we review recent advances in our understanding of SRPs focusing mainly on works published after 2000. The wealth of publications in this period, covering many diverse areas, is a testimony to the large environmental, biogeochemical and technological relevance of these organisms and how much the field has progressed in these years, although many important questions and applications remain to be explored.
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Genomic, proteomic, and biochemical analysis of the organohalide respiratory pathway in Desulfitobacterium dehalogenans. J Bacteriol 2014; 197:893-904. [PMID: 25512312 DOI: 10.1128/jb.02370-14] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Desulfitobacterium dehalogenans is able to grow by organohalide respiration using 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) as an electron acceptor. We used a combination of genome sequencing, biochemical analysis of redox active components, and shotgun proteomics to study elements of the organohalide respiratory electron transport chain. The genome of Desulfitobacterium dehalogenans JW/IU-DC1(T) consists of a single circular chromosome of 4,321,753 bp with a GC content of 44.97%. The genome contains 4,252 genes, including six rRNA operons and six predicted reductive dehalogenases. One of the reductive dehalogenases, CprA, is encoded by a well-characterized cprTKZEBACD gene cluster. Redox active components were identified in concentrated suspensions of cells grown on formate and Cl-OHPA or formate and fumarate, using electron paramagnetic resonance (EPR), visible spectroscopy, and high-performance liquid chromatography (HPLC) analysis of membrane extracts. In cell suspensions, these components were reduced upon addition of formate and oxidized after addition of Cl-OHPA, indicating involvement in organohalide respiration. Genome analysis revealed genes that likely encode the identified components of the electron transport chain from formate to fumarate or Cl-OHPA. Data presented here suggest that the first part of the electron transport chain from formate to fumarate or Cl-OHPA is shared. Electrons are channeled from an outward-facing formate dehydrogenase via menaquinones to a fumarate reductase located at the cytoplasmic face of the membrane. When Cl-OHPA is the terminal electron acceptor, electrons are transferred from menaquinones to outward-facing CprA, via an as-yet-unidentified membrane complex, and potentially an extracellular flavoprotein acting as an electron shuttle between the quinol dehydrogenase membrane complex and CprA.
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20
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Goris T, Schubert T, Gadkari J, Wubet T, Tarkka M, Buscot F, Adrian L, Diekert G. Insights into organohalide respiration and the versatile catabolism ofSulfurospirillum multivoransgained from comparative genomics and physiological studies. Environ Microbiol 2014; 16:3562-80. [DOI: 10.1111/1462-2920.12589] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 07/31/2014] [Indexed: 12/13/2022]
Affiliation(s)
- Tobias Goris
- Department of Applied and Ecological Microbiology; Institute of Microbiology; Friedrich Schiller University; Jena 07743 Germany
| | - Torsten Schubert
- Department of Applied and Ecological Microbiology; Institute of Microbiology; Friedrich Schiller University; Jena 07743 Germany
| | - Jennifer Gadkari
- Department of Applied and Ecological Microbiology; Institute of Microbiology; Friedrich Schiller University; Jena 07743 Germany
| | - Tesfaye Wubet
- Department of Soil Ecology; Helmholtz Centre for Environmental Research - UFZ; Halle 06120 Germany
| | - Mika Tarkka
- Department of Soil Ecology; Helmholtz Centre for Environmental Research - UFZ; Halle 06120 Germany
| | - Francois Buscot
- Department of Soil Ecology; Helmholtz Centre for Environmental Research - UFZ; Halle 06120 Germany
- German Centre for Integrative Biodiversity Research (iDiv) Halle - Jena - Leipzig; Leipzig 04103 Germany
| | - Lorenz Adrian
- Department Isotope Biogeochemistry; Helmholtz Centre for Environmental Research - UFZ; Leipzig 04318 Germany
| | - Gabriele Diekert
- Department of Applied and Ecological Microbiology; Institute of Microbiology; Friedrich Schiller University; Jena 07743 Germany
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21
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Vetriani C, Voordeckers JW, Crespo-Medina M, O'Brien CE, Giovannelli D, Lutz RA. Deep-sea hydrothermal vent Epsilonproteobacteria encode a conserved and widespread nitrate reduction pathway (Nap). ISME JOURNAL 2014; 8:1510-21. [PMID: 24430487 DOI: 10.1038/ismej.2013.246] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2013] [Revised: 12/01/2013] [Accepted: 12/03/2013] [Indexed: 11/10/2022]
Abstract
Despite the frequent isolation of nitrate-respiring Epsilonproteobacteria from deep-sea hydrothermal vents, the genes coding for the nitrate reduction pathway in these organisms have not been investigated in depth. In this study we have shown that the gene cluster coding for the periplasmic nitrate reductase complex (nap) is highly conserved in chemolithoautotrophic, nitrate-reducing Epsilonproteobacteria from deep-sea hydrothermal vents. Furthermore, we have shown that the napA gene is expressed in pure cultures of vent Epsilonproteobacteria and it is highly conserved in microbial communities collected from deep-sea vents characterized by different temperature and redox regimes. The diversity of nitrate-reducing Epsilonproteobacteria was found to be higher in moderate temperature, diffuse flow vents than in high temperature black smokers or in low temperatures, substrate-associated communities. As NapA has a high affinity for nitrate compared with the membrane-bound enzyme, its occurrence in vent Epsilonproteobacteria may represent an adaptation of these organisms to the low nitrate concentrations typically found in vent fluids. Taken together, our findings indicate that nitrate reduction is widespread in vent Epsilonproteobacteria and provide insight on alternative energy metabolism in vent microorganisms. The occurrence of the nap cluster in vent, commensal and pathogenic Epsilonproteobacteria suggests that the ability of these bacteria to respire nitrate is important in habitats as different as the deep-sea vents and the human body.
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Affiliation(s)
- Costantino Vetriani
- 1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - James W Voordeckers
- 1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - Melitza Crespo-Medina
- 1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - Charles E O'Brien
- 1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
| | - Donato Giovannelli
- 1] Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, NJ, USA [2] Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA [3] Institute of Marine Science - ISMAR, National Research Council of Italy, CNR, Ancona, Italy
| | - Richard A Lutz
- Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ, USA
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22
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Elhassanny AEM, Anderson ES, Menscher EA, Roop RM. The ferrous iron transporter FtrABCD is required for the virulence ofBrucella abortus2308 in mice. Mol Microbiol 2013; 88:1070-82. [DOI: 10.1111/mmi.12242] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/15/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Ahmed E. M. Elhassanny
- Department of Microbiology and Immunology; East Carolina University School of Medicine; Greenville; NC; 27834; USA
| | - Eric S. Anderson
- Department of Biology; East Carolina University School of Medicine; Greenville; NC; 27858; USA
| | - Evan A. Menscher
- Department of Microbiology and Immunology; East Carolina University School of Medicine; Greenville; NC; 27834; USA
| | - R. Martin Roop
- Department of Microbiology and Immunology; East Carolina University School of Medicine; Greenville; NC; 27834; USA
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23
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The prokaryotic Mo/W-bisPGD enzymes family: a catalytic workhorse in bioenergetic. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2013; 1827:1048-85. [PMID: 23376630 DOI: 10.1016/j.bbabio.2013.01.011] [Citation(s) in RCA: 103] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2012] [Revised: 01/21/2013] [Accepted: 01/23/2013] [Indexed: 01/05/2023]
Abstract
Over the past two decades, prominent importance of molybdenum-containing enzymes in prokaryotes has been put forward by studies originating from different fields. Proteomic or bioinformatic studies underpinned that the list of molybdenum-containing enzymes is far from being complete with to date, more than fifty different enzymes involved in the biogeochemical nitrogen, carbon and sulfur cycles. In particular, the vast majority of prokaryotic molybdenum-containing enzymes belong to the so-called dimethylsulfoxide reductase family. Despite its extraordinary diversity, this family is characterized by the presence of a Mo/W-bis(pyranopterin guanosine dinucleotide) cofactor at the active site. This review highlights what has been learned about the properties of the catalytic site, the modular variation of the structural organization of these enzymes, and their interplay with the isoprenoid quinones. In the last part, this review provides an integrated view of how these enzymes contribute to the bioenergetics of prokaryotes. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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Heylen K, Keltjens J. Redundancy and modularity in membrane-associated dissimilatory nitrate reduction in Bacillus. Front Microbiol 2012; 3:371. [PMID: 23087684 PMCID: PMC3475470 DOI: 10.3389/fmicb.2012.00371] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2012] [Accepted: 09/28/2012] [Indexed: 11/13/2022] Open
Abstract
The genomes of two phenotypically denitrifying type strains of the genus Bacillus were sequenced and the pathways for dissimilatory nitrate reduction were reconstructed. Results suggest that denitrification proceeds in the periplasmic space and in an analogous fashion as in Gram-negative organisms, yet with the participation of proteins that tend to be membrane-bound or membrane-associated. A considerable degree of functional redundancy was observed with marked differences between B. azotoformans LMG 9581(T) and B. bataviensis LMG 21833(T). In addition to the already characterized menaquinol/cyt c-dependent nitric oxide reductase (Suharti et al., 2001, 2004) of which the encoding genes could be identified now, evidence for another novel nitric oxide reductase (NOR) was found. Also, our analyses confirm earlier findings on branched electron transfer with both menaquinol and cytochrome c as reductants. Quite unexpectedly, both bacilli have the disposal of two parallel pathways for nitrite reduction enabling a life style as a denitrifier and as an ammonifying bacterium.
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Affiliation(s)
- Kim Heylen
- Laboratory of Microbiology, Department of Biochemistry and Microbiology, University of Ghent Gent, Belgium
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25
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Simon J, Klotz MG. Diversity and evolution of bioenergetic systems involved in microbial nitrogen compound transformations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:114-35. [PMID: 22842521 DOI: 10.1016/j.bbabio.2012.07.005] [Citation(s) in RCA: 214] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2012] [Revised: 07/10/2012] [Accepted: 07/19/2012] [Indexed: 11/18/2022]
Abstract
Nitrogen is an essential element of life that needs to be assimilated in its most reduced form, ammonium. On the other hand, nitrogen exists in a multitude of oxidation states and, consequently, nitrogen compounds (NCs) serve as electron donor and/or acceptors in many catabolic pathways including various forms of microbial respiration that contribute to the global biogeochemical nitrogen cycle. Some of these NCs are also known as reactive nitrogen species able to cause nitrosative stress because of their high redox reactivity. The best understood processes of the nitrogen cycle are denitrification and ammonification (both beginning with nitrate reduction to nitrite), nitrification (aerobic oxidation of ammonium and nitrite) and anaerobic ammonium oxidation (anammox). This review presents examples of the diverse architecture, either elucidated or anticipated, and the high degree of modularity of the corresponding respiratory electron transport processes found in Bacteria and Archaea, and relates these to their respective bioenergetic mechanisms of proton motive force generation. In contrast to the multiplicity of enzymes that catalyze NC transformations, the number of proteins or protein modules involved in connecting electron transport to and from these enzymes with the quinone/quinol pool is comparatively small. These quinone/quinol-reactive protein modules consist of cytochromes b and c and iron-sulfur proteins. Conclusions are drawn towards the evolutionary relationships of bioenergetic systems involved in NC transformation and deduced aspects of the evolution of the biogeochemical nitrogen cycle are presented. This article is part of a Special Issue entitled: The evolutionary aspects of bioenergetic systems.
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Affiliation(s)
- Jörg Simon
- Microbial Energy Conversion and Biotechnology, Department of Biology, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany.
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26
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Abstract
Dissimilatory sulfate and sulfur reduction evolved billions of years ago and while the bacteria and archaea that use this unique metabolism employ a variety of electron donors, H(2) is most commonly used as the energy source. These prokaryotes use multiheme c-type proteins to shuttle electrons from electron donors, and electron transport complexes presumed to contain b-type hemoproteins contribute to proton charging of the membrane. Numerous sulfate and sulfur reducers use an alternate pathway for heme synthesis and, frequently, uniquely specific axial ligands are used to secure c-type heme to the protein. This review presents some of the types and functional activities of hemoproteins involved in these two dissimilatory reduction pathways.
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Kern M, Klotz MG, Simon J. The Wolinella succinogenes mcc gene cluster encodes an unconventional respiratory sulphite reduction system. Mol Microbiol 2011; 82:1515-30. [DOI: 10.1111/j.1365-2958.2011.07906.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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28
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Kraft B, Strous M, Tegetmeyer HE. Microbial nitrate respiration – Genes, enzymes and environmental distribution. J Biotechnol 2011; 155:104-17. [DOI: 10.1016/j.jbiotec.2010.12.025] [Citation(s) in RCA: 223] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Revised: 12/07/2010] [Accepted: 12/20/2010] [Indexed: 01/13/2023]
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Respiratory nitrogen metabolism and nitrosative stress defence in ϵ-proteobacteria: the role of NssR-type transcription regulators. Biochem Soc Trans 2011; 39:299-302. [PMID: 21265792 DOI: 10.1042/bst0390299] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
ϵ-Proteobacteria form a globally ubiquitous group of ecologically significant organisms and comprise a diverse range of host-associated and free-living species. To grow by anaerobic respiration, many ϵ-proteobacteria reduce nitrate to nitrite followed by either nitrite ammonification or denitrification. Using the ammonifying model organisms Wolinella succinogenes and Campylobacter jejuni, the electron transport chains of nitrate respiration, respiratory nitrite ammonification and even N2O (nitrous oxide) respiration have been characterized in recent years, but knowledge on nitrosative stress defence, nitrogen compound-sensing and corresponding signal transduction pathways is limited. The potentially dominant role of NssR (nitrosative stress-sensing regulator)-type transcription regulators in ϵ-proteobacterial nitrogen metabolism is discussed.
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Physiological and evolutionary studies of NAP systems in Shewanella piezotolerans WP3. ISME JOURNAL 2010; 5:843-55. [PMID: 21124486 DOI: 10.1038/ismej.2010.182] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Most of the Shewanella species contain two periplasmic nitrate reductases (NAP-α and NAP-β), which is a unique feature of this genus. In the present study, the physiological function and evolutionary relationship of the two NAP systems were studied in the deep-sea bacterium Shewanella piezotolerans WP3. Both of the WP3 nap gene clusters: nap-α (napD1A1B1C) and nap-β (napD2A2B2) were shown to be involved in nitrate respiration. Phylogenetic analyses suggest that NAP-β originated earlier than NAP-α. Tetraheme cytochromes NapC and CymA were found to be the major electron deliver proteins, and CymA also served as a sole electron transporter towards nitrite reductase. Interestingly, a ΔnapA2 mutant with the single functional NAP-α system showed better growth than the wild-type strain, when grown in nitrate medium, and it had a selective advantage to the wild-type strain. On the basis of these results, we proposed the evolution direction of nitrate respiration system in Shewanella: from a single NAP-β to NAP-β and NAP-α both, followed by the evolution to a single NAP-α. Moreover, the data presented here will be very useful for the designed engineering of Shewanella for more efficient respiring capabilities for environmental bioremediation.
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Kern M, Scheithauer J, Kranz RG, Simon J. Essential histidine pairs indicate conserved haem binding in epsilonproteobacterial cytochrome c haem lyases. MICROBIOLOGY-SGM 2010; 156:3773-3781. [PMID: 20705660 PMCID: PMC3068706 DOI: 10.1099/mic.0.042838-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Bacterial cytochrome c maturation occurs at the outside of the cytoplasmic membrane, requires transport of haem b across the membrane, and depends on membrane-bound cytochrome c haem lyase (CCHL), an enzyme that catalyses covalent attachment of haem b to apocytochrome c. Epsilonproteobacteria such as Wolinella succinogenes use the cytochrome c biogenesis system II and contain unusually large CCHL proteins of about 900 amino acid residues that appear to be fusions of the CcsB and CcsA proteins found in other bacteria. CcsBA-type CCHLs have been proposed to act as haem transporters that contain two haem b coordination sites located at different sides of the membrane and formed by histidine pairs. W. succinogenes cells contain three CcsBA-type CCHL isoenzymes (NrfI, CcsA1 and CcsA2) that are known to differ in their specificity for apocytochromes and apparently recognize different haem c binding motifs such as CX2CH (by CcsA2), CX2CK (by NrfI) and CX15CH (by CcsA1). In this study, conserved histidine residues were individually replaced by alanine in each of the W. succinogenes CCHLs. Characterization of NrfI and CcsA1 variants in W. succinogenes demonstrated that a set of four histidines is essential for maturing the dedicated multihaem cytochromes c NrfA and MccA, respectively. The function of W. succinogenes CcsA2 variants produced in Escherichia coli was also found to depend on each of these four conserved histidine residues. The presence of imidazole in the growth medium of both W. succinogenes and E. coli rescued the cytochrome c biogenesis activity of most histidine variants, albeit to different extents, thereby implying the presence of two functionally distinct histidine pairs in each CCHL. The data support a model in which two conserved haem b binding sites are involved in haem transport catalysed by CcsBA-type CCHLs.
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Affiliation(s)
- Melanie Kern
- Institute of Microbiology and Genetics, Department of Biology, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Juliane Scheithauer
- Institute of Microbiology and Genetics, Department of Biology, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Robert G Kranz
- Department of Biology, Washington University, 1 Brookings Drive, St Louis, MO 63130, USA
| | - Jörg Simon
- Institute of Microbiology and Genetics, Department of Biology, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
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Simpson PJL, Richardson DJ, Codd R. The periplasmic nitrate reductase in Shewanella: the resolution, distribution and functional implications of two NAP isoforms, NapEDABC and NapDAGHB. MICROBIOLOGY-SGM 2009; 156:302-312. [PMID: 19959582 DOI: 10.1099/mic.0.034421-0] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In the bacterial periplasm, the reduction of nitrate to nitrite is catalysed by a periplasmic nitrate reductase (NAP) system, which is a species-dependent assembly of protein subunits encoded by the nap operon. The reduction of nitrate catalysed by NAP takes place in the 90 kDa NapA subunit, which contains a Mo-bis-molybdopterin guanine dinucleotide cofactor and one [4Fe-4S] iron-sulfur cluster. A review of the nap operons in the genomes of 19 strains of Shewanella shows that most genomes contain two nap operons. This is an unusual feature of this genus. The two NAP isoforms each comprise three isoform-specific subunits - NapA, a di-haem cytochrome NapB, and a maturation chaperone NapD - but have different membrane-intrinsic subunits, and have been named NAP-alpha (NapEDABC) and NAP-beta (NapDAGHB). Sixteen Shewanella genomes encode both NAP-alpha and NAP-beta. The genome of the vigorous denitrifier Shewanella denitrificans OS217 encodes only NAP-alpha and the genome of the respiratory nitrate ammonifier Shewanella oneidensis MR-1 encodes only NAP-beta. This raises the possibility that NAP-alpha and NAP-beta are associated with physiologically distinct processes in the environmentally adaptable genus Shewanella.
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Affiliation(s)
- Philippa J L Simpson
- Centre for Heavy Metals Research, School of Chemistry, University of Sydney, New South Wales 2006, Australia
| | - David J Richardson
- School of Biological Sciences, University of East Anglia, Norwich NR4 TJ7, UK
| | - Rachel Codd
- School of Medical Sciences (Pharmacology) and Bosch Institute, University of Sydney, New South Wales 2006, Australia.,Centre for Heavy Metals Research, School of Chemistry, University of Sydney, New South Wales 2006, Australia
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Kern M, Simon J. Periplasmic nitrate reduction in Wolinella succinogenes: cytoplasmic NapF facilitates NapA maturation and requires the menaquinol dehydrogenase NapH for membrane attachment. Microbiology (Reading) 2009; 155:2784-2794. [DOI: 10.1099/mic.0.029983-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Various nitrate-reducing bacteria produce proteins of the periplasmic nitrate reductase (Nap) system to catalyse electron transport from the membraneous quinol pool to the periplasmic nitrate reductase NapA. The composition of the corresponding nap gene clusters varies but, in addition to napA, genes encoding at least one membrane-bound quinol dehydrogenase module (NapC and/or NapGH) are regularly present. Moreover, some nap loci predict accessory proteins such as the iron–sulfur protein NapF, whose function is poorly understood. Here, the role of NapF in nitrate respiration of the Epsilonproteobacterium Wolinella succinogenes was examined. Immunoblot analysis showed that NapF is located in the membrane fraction in nitrate-grown wild-type cells whereas it was found to be a soluble cytoplasmic protein in a napH deletion mutant. This finding indicates the formation of a membrane-bound NapGHF complex that is likely to catalyse NapH-dependent menaquinol oxidation and electron transport to the iron–sulfur adaptor proteins NapG and NapF, which are located on the periplasmic and cytoplasmic side of the membrane, respectively. The cysteine residues of a CX3CP motif and of the C-terminal tetra-cysteine cluster of NapH were found to be required for interaction with NapF. A napF deletion mutant accumulated the catalytically inactive cytoplasmic NapA precursor, suggesting that electron flow or direct interaction between NapF and NapA facilitated NapA assembly and/or export. On the other hand, NapA maturation and activity was not impaired in the absence of NapH, demonstrating that soluble NapF is functional. Each of the four tetra-cysteine motifs of NapF was modified but only one motif was found to be essential for efficient NapA maturation. It is concluded that the NapGHF complex plays a multifunctional role in menaquinol oxidation, electron transfer to periplasmic NapA and maturation of the cytoplasmic NapA precursor.
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Affiliation(s)
- Melanie Kern
- Institute of Molecular Biosciences, Goethe University, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
- Department of Microbiology and Genetics, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
| | - Jörg Simon
- Institute of Molecular Biosciences, Goethe University, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
- Department of Microbiology and Genetics, Technische Universität Darmstadt, Schnittspahnstr. 10, 64287 Darmstadt, Germany
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Gao H, Yang ZK, Barua S, Reed SB, Romine MF, Nealson KH, Fredrickson JK, Tiedje JM, Zhou J. Reduction of nitrate in Shewanella oneidensis depends on atypical NAP and NRF systems with NapB as a preferred electron transport protein from CymA to NapA. ISME JOURNAL 2009; 3:966-76. [DOI: 10.1038/ismej.2009.40] [Citation(s) in RCA: 105] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kern M, Simon J. Electron transport chains and bioenergetics of respiratory nitrogen metabolism in Wolinella succinogenes and other Epsilonproteobacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:646-56. [PMID: 19171117 DOI: 10.1016/j.bbabio.2008.12.010] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2008] [Accepted: 12/23/2008] [Indexed: 12/16/2022]
Abstract
Recent phylogenetic analyses have established that the Epsilonproteobacteria form a globally ubiquitous group of ecologically significant organisms that comprises a diverse range of free-living bacteria as well as host-associated organisms like Wolinella succinogenes and pathogenic Campylobacter and Helicobacter species. Many Epsilonproteobacteria reduce nitrate and nitrite and perform either respiratory nitrate ammonification or denitrification. The inventory of epsilonproteobacterial genomes from 21 different species was analysed with respect to key enzymes involved in respiratory nitrogen metabolism. Most ammonifying Epsilonproteobacteria employ two enzymic electron transport systems named Nap (periplasmic nitrate reductase) and Nrf (periplasmic cytochrome c nitrite reductase). The current knowledge on the architecture and function of the corresponding proton motive force-generating respiratory chains using low-potential electron donors are reviewed in this article and the role of membrane-bound quinone/quinol-reactive proteins (NapH and NrfH) that are representative of widespread bacterial electron transport modules is highlighted. Notably, all Epsilonproteobacteria lack a napC gene in their nap gene clusters. Possible roles of the Nap and Nrf systems in anabolism and nitrosative stress defence are also discussed. Free-living denitrifying Epsilonproteobacteria lack the Nrf system but encode cytochrome cd(1) nitrite reductase, at least one nitric oxide reductase and a characteristic cytochrome c nitrous oxide reductase system (cNosZ). Interestingly, cNosZ is also found in some ammonifying Epsilonproteobacteria and enables nitrous oxide respiration in W. succinogenes.
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Affiliation(s)
- Melanie Kern
- Institute of Molecular Biosciences, Goethe University, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
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Simon J, van Spanning RJ, Richardson DJ. The organisation of proton motive and non-proton motive redox loops in prokaryotic respiratory systems. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1480-90. [DOI: 10.1016/j.bbabio.2008.09.008] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2008] [Revised: 09/08/2008] [Accepted: 09/09/2008] [Indexed: 10/21/2022]
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Quinone-reactive proteins devoid of haem b form widespread membrane-bound electron transport modules in bacterial respiration. Biochem Soc Trans 2008; 36:1011-6. [DOI: 10.1042/bst0361011] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Many quinone-reactive enzyme complexes that are part of membrane-integral eukaryotic or prokaryotic respiratory electron transport chains contain one or more haem b molecules embedded in the membrane. In recent years, various novel proteins have emerged that are devoid of haem b but are thought to fulfil a similar function in bacterial anaerobic respiratory systems. These proteins are encoded by genes organized in various genomic arrangements and are thought to form widespread membrane-bound quinone-reactive electron transport modules that exchange electrons with redox partner proteins located at the outer side of the cytoplasmic membrane. Prototypic representatives are the multihaem c-type cytochromes NapC, NrfH and TorC (NapC/NrfH family), the putative iron–sulfur protein NapH and representatives of the NrfD/PsrC family. Members of these protein families vary in the number of their predicted transmembrane segments and, consequently, diverse quinone-binding sites are expected. Only a few of these enzymes have been isolated and characterized biochemically and high-resolution structures are limited. This mini-review briefly summarizes predicted and experimentally demonstrated properties of the proteins in question and discusses their role in electron transport and bioenergetics of anaerobic respiration.
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