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Kawai S, Martinez JN, Lichtenberg M, Trampe E, Kühl M, Tank M, Haruta S, Nishihara A, Hanada S, Thiel V. In-Situ Metatranscriptomic Analyses Reveal the Metabolic Flexibility of the Thermophilic Anoxygenic Photosynthetic Bacterium Chloroflexus aggregans in a Hot Spring Cyanobacteria-Dominated Microbial Mat. Microorganisms 2021; 9:microorganisms9030652. [PMID: 33801086 PMCID: PMC8004040 DOI: 10.3390/microorganisms9030652] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 03/17/2021] [Accepted: 03/17/2021] [Indexed: 12/13/2022] Open
Abstract
Chloroflexus aggregans is a metabolically versatile, thermophilic, anoxygenic phototrophic member of the phylum Chloroflexota (formerly Chloroflexi), which can grow photoheterotrophically, photoautotrophically, chemoheterotrophically, and chemoautotrophically. In hot spring-associated microbial mats, C. aggregans co-exists with oxygenic cyanobacteria under dynamic micro-environmental conditions. To elucidate the predominant growth modes of C. aggregans, relative transcription levels of energy metabolism- and CO2 fixation-related genes were studied in Nakabusa Hot Springs microbial mats over a diel cycle and correlated with microscale in situ measurements of O2 and light. Metatranscriptomic analyses indicated two periods with different modes of energy metabolism of C. aggregans: (1) phototrophy around midday and (2) chemotrophy in the early morning hours. During midday, C. aggregans mainly employed photoheterotrophy when the microbial mats were hyperoxic (400–800 µmol L−1 O2). In the early morning hours, relative transcription peaks of genes encoding uptake hydrogenase, key enzymes for carbon fixation, respiratory complexes as well as enzymes for TCA cycle and acetate uptake suggest an aerobic chemomixotrophic lifestyle. This is the first in situ study of the versatile energy metabolism of C. aggregans based on gene transcription patterns. The results provide novel insights into the metabolic flexibility of these filamentous anoxygenic phototrophs that thrive under dynamic environmental conditions.
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Affiliation(s)
- Shigeru Kawai
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
- Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa 237-0061, Japan
- Correspondence: (S.K.); (V.T.)
| | - Joval N. Martinez
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
- Department of Natural Sciences, College of Arts and Sciences, University of St. La Salle, Bacolod City, Negros Occidental 6100, Philippines
| | - Mads Lichtenberg
- Department of Biology, Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark; (M.L.); (E.T.); (M.K.)
| | - Erik Trampe
- Department of Biology, Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark; (M.L.); (E.T.); (M.K.)
| | - Michael Kühl
- Department of Biology, Marine Biological Section, University of Copenhagen, Strandpromenaden 5, 3000 Helsingør, Denmark; (M.L.); (E.T.); (M.K.)
| | - Marcus Tank
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
- DSMZ—German Culture Collection of Microorganisms and Cell Culture, GmbH Inhoffenstraße 7B, 38124 Braunschweig, Germany
| | - Shin Haruta
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
| | - Arisa Nishihara
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ibaraki 305-8566, Japan
| | - Satoshi Hanada
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
| | - Vera Thiel
- Department of Biological Sciences, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan; (J.N.M.); (M.T.); (S.H.); (A.N.); (S.H.)
- DSMZ—German Culture Collection of Microorganisms and Cell Culture, GmbH Inhoffenstraße 7B, 38124 Braunschweig, Germany
- Correspondence: (S.K.); (V.T.)
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Dewey ED, Stokes LM, Burchell BM, Shaffer KN, Huntington AM, Baker JM, Nadendla S, Giglio MG, Bender KS, Touchman JW, Blankenship RE, Madigan MT, Sattley WM. Analysis of the Complete Genome of the Alkaliphilic and Phototrophic Firmicute Heliorestis convoluta Strain HH T. Microorganisms 2020; 8:E313. [PMID: 32106460 PMCID: PMC7143216 DOI: 10.3390/microorganisms8030313] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2020] [Revised: 02/16/2020] [Accepted: 02/22/2020] [Indexed: 11/16/2022] Open
Abstract
Despite significant interest and past work to elucidate the phylogeny and photochemistry of species of the Heliobacteriaceae, genomic analyses of heliobacteria to date have been limited to just one published genome, that of the thermophilic species Heliobacterium (Hbt.) modesticaldum str. Ice1T. Here we present an analysis of the complete genome of a second heliobacterium, Heliorestis (Hrs.) convoluta str. HHT, an alkaliphilic, mesophilic, and morphologically distinct heliobacterium isolated from an Egyptian soda lake. The genome of Hrs. convoluta is a single circular chromosome of 3.22 Mb with a GC content of 43.1% and 3263 protein-encoding genes. In addition to culture-based observations and insights gleaned from the Hbt. modesticaldum genome, an analysis of enzyme-encoding genes from key metabolic pathways supports an obligately photoheterotrophic lifestyle for Hrs. convoluta. A complete set of genes encoding enzymes for propionate and butyrate catabolism and the absence of a gene encoding lactate dehydrogenase distinguishes the carbon metabolism of Hrs. convoluta from its close relatives. Comparative analyses of key proteins in Hrs. convoluta, including cytochrome c553 and the Fo alpha subunit of ATP synthase, with those of related species reveal variations in specific amino acid residues that likely contribute to the success of Hrs. convoluta in its highly alkaline environment.
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Affiliation(s)
- Emma D. Dewey
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Lynn M. Stokes
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Brad M. Burchell
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Kathryn N. Shaffer
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Austin M. Huntington
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Jennifer M. Baker
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
| | - Suvarna Nadendla
- Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD 21201, USA; (S.N.); (M.G.G.)
| | - Michelle G. Giglio
- Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, MD 21201, USA; (S.N.); (M.G.G.)
| | - Kelly S. Bender
- Department of Microbiology, Southern Illinois University, Carbondale, IL 62901, USA; (K.S.B.); (M.T.M.)
| | | | - Robert E. Blankenship
- Departments of Biology and Chemistry, Washington University in Saint Louis, St. Louis, MO 63130, USA;
| | - Michael T. Madigan
- Department of Microbiology, Southern Illinois University, Carbondale, IL 62901, USA; (K.S.B.); (M.T.M.)
| | - W. Matthew Sattley
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN 46953, USA; (E.D.D.); (L.M.S.); (B.M.B.); (K.N.S.); (A.M.H.); (J.M.B.)
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Buckel W, Thauer RK. Flavin-Based Electron Bifurcation, A New Mechanism of Biological Energy Coupling. Chem Rev 2018; 118:3862-3886. [PMID: 29561602 DOI: 10.1021/acs.chemrev.7b00707] [Citation(s) in RCA: 189] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
There are two types of electron bifurcation (EB), either quinone- or flavin-based (QBEB/FBEB), that involve reduction of a quinone or flavin by a two-electron transfer and two reoxidations by a high- and low-potential one-electron acceptor with a reactive semiquinone intermediate. In QBEB, the reduced low-potential acceptor (cytochrome b) is exclusively used to generate ΔμH+. In FBEB, the "energy-rich" low-potential reduced ferredoxin or flavodoxin has dual function. It can give rise to ΔμH+/Na+ via a ferredoxin:NAD reductase (Rnf) or ferredoxin:proton reductase (Ech) or conducts difficult reductions such as CO2 to CO. The QBEB membrane complexes are similar in structure and function and occur in all domains of life. In contrast, FBEB complexes are soluble and occur only in strictly anaerobic bacteria and archaea (FixABCX being an exception). The FBEB complexes constitute a group consisting of four unrelated families that contain (1) electron-transferring flavoproteins (EtfAB), (2) NAD(P)H dehydrogenase (NuoF homologues), (3) heterodisulfide reductase (HdrABC) or HdrABC homologues, and (4) NADH-dependent ferredoxin:NADP reductase (NfnAB). The crystal structures and electron transport of EtfAB-butyryl-CoA dehydrogenase and NfnAB are compared with those of complex III of the respiratory chain (cytochrome bc1), whereby unexpected common features have become apparent.
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Affiliation(s)
- Wolfgang Buckel
- Fachbereich Biologie , Philipps-Universität , 35032 Marburg , Germany.,Max-Planck-Institut für Terrestrische Mikrobiologie , 35043 Marburg , Germany
| | - Rudolf K Thauer
- Fachbereich Biologie , Philipps-Universität , 35032 Marburg , Germany.,Max-Planck-Institut für Terrestrische Mikrobiologie , 35043 Marburg , Germany
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From low- to high-potential bioenergetic chains: Thermodynamic constraints of Q-cycle function. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2016; 1857:1569-1579. [DOI: 10.1016/j.bbabio.2016.06.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 06/14/2016] [Accepted: 06/16/2016] [Indexed: 11/27/2022]
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Abstract
Quinol oxidation in the catalytic quinol oxidation site (Qo site) of cytochrome (cyt) bc1 complexes is the key step of the Q cycle mechanism, which laid the ground for Mitchell’s chemiosmotic theory of energy conversion. Bifurcated electron transfer upon quinol oxidation enables proton uptake and release on opposite membrane sides, thus generating a proton gradient that fuels ATP synthesis in cellular respiration and photosynthesis. The Qo site architecture formed by cyt b and Rieske iron–sulfur protein (ISP) impedes harmful bypass reactions. Catalytic importance is assigned to four residues of cyt b formerly described as PEWY motif in the context of mitochondrial complexes, which we now denominate Qo motif as comprehensive evolutionary sequence analysis of cyt b shows substantial natural variance of the motif with phylogenetically specific patterns. In particular, the Qo motif is identified as PEWY in mitochondria, α- and ε-Proteobacteria, Aquificae, Chlorobi, Cyanobacteria, and chloroplasts. PDWY is present in Gram-positive bacteria, Deinococcus–Thermus and haloarchaea, and PVWY in β- and γ-Proteobacteria. PPWF only exists in Archaea. Distinct patterns for acidophilic organisms indicate environment-specific adaptations. Importantly, the presence of PDWY and PEWY is correlated with the redox potential of Rieske ISP and quinone species. We propose that during evolution from low to high potential electron-transfer systems in the emerging oxygenic atmosphere, cyt bc1 complexes with PEWY as Qo motif prevailed to efficiently use high potential ubiquinone as substrate, whereas cyt b with PDWY operate best with low potential Rieske ISP and menaquinone, with the latter being the likely composition of the ancestral cyt bc1 complex.
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Affiliation(s)
- Wei-Chun Kao
- Institute for Biochemistry and Molecular Biology, ZBMZ, BIOSS Centre for Biological Signalling Studies, University of Freiburg, Germany
- Faculty of Biology, University of Freiburg, Germany
| | - Carola Hunte
- Institute for Biochemistry and Molecular Biology, ZBMZ, BIOSS Centre for Biological Signalling Studies, University of Freiburg, Germany
- *Corresponding author: E-mail:
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Redding KE, Sarrou I, Rappaport F, Santabarbara S, Lin S, Reifschneider KT. Modulation of the fluorescence yield in heliobacterial cells by induction of charge recombination in the photosynthetic reaction center. PHOTOSYNTHESIS RESEARCH 2014; 120:221-235. [PMID: 24318506 DOI: 10.1007/s11120-013-9957-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2013] [Accepted: 11/25/2013] [Indexed: 06/02/2023]
Abstract
Heliobacteria contain a very simple photosynthetic apparatus, consisting of a homodimeric type I reaction center (RC) without a peripheral antenna system and using the unique pigment bacteriochlorophyll (BChl) g. They are thought to use a light-driven cyclic electron transport pathway to pump protons, and thereby phosphorylate ADP, although some of the details of this cycle are yet to be worked out. We previously reported that the fluorescence emission from the heliobacterial RC in vivo was increased by exposure to actinic light, although this variable fluorescence phenomenon exhibited very different characteristics to that in oxygenic phototrophs (Collins et al. 2010). Here, we describe the underlying mechanism behind the variable fluorescence in heliobacterial cells. We find that the ability to stably photobleach P800, the primary donor of the RC, using brief flashes is inversely correlated to the variable fluorescence. Using pump-probe spectroscopy in the nanosecond timescale, we found that illumination of cells with bright light for a few seconds put them in a state in which a significant fraction of the RCs underwent charge recombination from P800 (+)A0 (-) with a time constant of ~20 ns. The fraction of RCs in the rapidly back-reacting state correlated very well with the variable fluorescence, indicating that nearly all of the increase in fluorescence could be explained by charge recombination of P800 (+)A0 (-), some of which regenerated the singlet excited state. This hypothesis was tested directly by time-resolved fluorescence studies in the ps and ns timescales. The major decay component in whole cells had a 20-ps decay time, representing trapping by the RC. Treatment of cells with dithionite resulted in the appearance of a ~18-ns decay component, which accounted for ~0.6 % of the decay, but was almost undetectable in the untreated cells. We conclude that strong illumination of heliobacterial cells can result in saturation of the electron acceptor pool, leading to reduction of the acceptor side of the RC and the creation of a back-reacting RC state that gives rise to delayed fluorescence.
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Affiliation(s)
- Kevin E Redding
- Department of Chemistry and Biochemistry, Arizona State University, 1711 S. Rural Rd., Tempe, AZ, 85287-1604, USA,
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Energy Conservation in Heliobacteria: Photosynthesis and Central Carbon Metabolism. THE STRUCTURAL BASIS OF BIOLOGICAL ENERGY GENERATION 2014. [DOI: 10.1007/978-94-017-8742-0_13] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Baymann F, Schoepp-Cothenet B, Lebrun E, van Lis R, Nitschke W. Phylogeny of Rieske/cytb complexes with a special focus on the Haloarchaeal enzymes. Genome Biol Evol 2012; 4:720-9. [PMID: 22798450 PMCID: PMC3509893 DOI: 10.1093/gbe/evs056] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Rieske/cytochrome b (Rieske/cytb) complexes are proton pumping quinol oxidases that are present in most bacteria and Archaea. The phylogeny of their subunits follows closely the 16S-rRNA phylogeny, indicating that chemiosmotic coupling was already present in the last universal common ancestor of Archaea and bacteria. Haloarchaea are the only organisms found so far that acquired Rieske/cytb complexes via interdomain lateral gene transfer. They encode two Rieske/cytb complexes in their genomes; one of them is found in genetic context with nitrate reductase genes and has its closest relatives among Actinobacteria and the Thermus/Deinococcus group. It is likely to function in nitrate respiration. The second Rieske/cytb complex of Haloarchaea features a split cytochrome b sequence as do Cyanobacteria, chloroplasts, Heliobacteria, and Bacilli. It seems that Haloarchaea acquired this complex from an ancestor of the above-mentioned phyla. Its involvement in the bioenergetic reaction chains of Haloarchaea is unknown. We present arguments in favor of the hypothesis that the ancestor of Haloarchaea, which relied on a highly specialized bioenergetic metabolism, that is, methanogenesis, and was devoid of quinones and most enzymes of anaerobic or aerobic bioenergetic reaction chains, integrated laterally transferred genes into its genome to respond to a change in environmental conditions that made methanogenesis unfavorable.
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Kargul J, Barber J. Structure and Function of Photosynthetic Reaction Centres. MOLECULAR SOLAR FUELS 2011. [DOI: 10.1039/9781849733038-00107] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Extensive biochemical, biophysical, molecular biological and structural studies on a wide range of prokaryotic and eukaryotic photosynthetic organisms has revealed common features of their reaction centres where light induced charge separation and stabilization occurs. There is little doubt that all reaction centres have evolved from a common ancestor and have been optimized to maximum efficiency. As such they provide principles that can be used as a blueprint for developing artificial photo-electrochemical catalytic systems to generate solar fuels. This chapter summarises the common features of the organization of cofactors, electron transfer pathways and protein environments of reaction centres of anoxygenic and oxygenic phototrophs. In particular, the latest molecular details derived from X-ray crystallography are discussed in context of the specific catalytic functions of the Type I and Type II reaction centres.
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Affiliation(s)
- Joanna Kargul
- Division of Molecular Biosciences, Faculty of Natural Sciences Imperial College London, London, SW7 2AZ UK
| | - James Barber
- Division of Molecular Biosciences, Faculty of Natural Sciences Imperial College London, London, SW7 2AZ UK
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Expression and characterization of the diheme cytochrome c subunit of the cytochrome bc complex in Heliobacterium modesticaldum. Arch Biochem Biophys 2011; 517:131-7. [PMID: 22119137 DOI: 10.1016/j.abb.2011.11.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Revised: 11/07/2011] [Accepted: 11/08/2011] [Indexed: 11/23/2022]
Abstract
Heliobacterium modesticaldum is a Gram-positive, anaerobic, anoxygenic photoheterotrophic bacterium. Its cytochrome bc complex (Rieske/cyt b complex) has some similarities to cytochrome b(6)f complexes from cyanobacteria and chloroplasts, and also shares some characteristics of typical bacterial cytochrome bc(1) complexes. One of the unique factors of the heliobacterial cytochrome bc complex is the presence of a diheme cytochrome c instead of the monoheme cytochrome f in the cytochrome b(6)f complex or the monoheme cytochrome c(1) in the bc(1) complex. To understand the structure and function of this diheme cytochrome c protein, we expressed the N-terminal transmembrane-helix-truncated soluble H. modesticaldum diheme cytochrome c in Escherichia coli. This 25kDa recombinant protein possesses two c-type hemes, confirmed by mass spectrometry and a variety of biochemical techniques. Sequence analysis of the H. modesticaldum diheme cytochrome c indicates that it may have originated from gene duplication and subsequent gene fusion, as in cytochrome c(4) proteins. The recombinant protein exhibits a single redox midpoint potential of +71mV versus NHE, which indicates that the two hemes have very similar protein environments.
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Tang KH, Tang YJ, Blankenship RE. Carbon metabolic pathways in phototrophic bacteria and their broader evolutionary implications. Front Microbiol 2011; 2:165. [PMID: 21866228 PMCID: PMC3149686 DOI: 10.3389/fmicb.2011.00165] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2011] [Accepted: 07/18/2011] [Indexed: 11/19/2022] Open
Abstract
Photosynthesis is the biological process that converts solar energy to biomass, bio-products, and biofuel. It is the only major natural solar energy storage mechanism on Earth. To satisfy the increased demand for sustainable energy sources and identify the mechanism of photosynthetic carbon assimilation, which is one of the bottlenecks in photosynthesis, it is essential to understand the process of solar energy storage and associated carbon metabolism in photosynthetic organisms. Researchers have employed physiological studies, microbiological chemistry, enzyme assays, genome sequencing, transcriptomics, and (13)C-based metabolomics/fluxomics to investigate central carbon metabolism and enzymes that operate in phototrophs. In this report, we review diverse CO(2) assimilation pathways, acetate assimilation, carbohydrate catabolism, the tricarboxylic acid cycle and some key, and/or unconventional enzymes in central carbon metabolism of phototrophic microorganisms. We also discuss the reducing equivalent flow during photoautotrophic and photoheterotrophic growth, evolutionary links in the central carbon metabolic network, and correlations between photosynthetic and non-photosynthetic organisms. Considering the metabolic versatility in these fascinating and diverse photosynthetic bacteria, many essential questions in their central carbon metabolism still remain to be addressed.
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Affiliation(s)
- Kuo-Hsiang Tang
- Department of Biology, Washington University in St. LouisSt. Louis, MO, USA
- Department of Chemistry, Washington University in St. LouisSt. Louis, MO, USA
| | - Yinjie J. Tang
- Department of Energy, Environment, and Chemical Engineering, Washington University in St. LouisSt. Louis, MO, USA
| | - Robert Eugene Blankenship
- Department of Biology, Washington University in St. LouisSt. Louis, MO, USA
- Department of Chemistry, Washington University in St. LouisSt. Louis, MO, USA
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Collins AM, Redding KE, Blankenship RE. Modulation of fluorescence in Heliobacterium modesticaldum cells. PHOTOSYNTHESIS RESEARCH 2010; 104:283-292. [PMID: 20461555 DOI: 10.1007/s11120-010-9554-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2009] [Accepted: 04/14/2010] [Indexed: 05/29/2023]
Abstract
In what appears to be a common theme for all phototrophs, heliobacteria exhibit complex modulations of fluorescence yield when illuminated with actinic light and probed on a time scale of micros to minutes. The fluorescence yield from cells of Heliobacterium modesticaldum remained nearly constant for the first 10-100 ms of illumination and then rose to a maximum level with one or two inflections over the course of many seconds. Fluorescence then declined to a steady-state value within about one minute. In this analysis, the origins of the fluorescence induction in whole cells of heliobacteria are investigated by treating cells with a combination of electron accepters, donors, and inhibitors of the photosynthetic electron transport, as well as varying the temperature. We conclude that fluorescence modulation in H. modesticaldum results from acceptor-side limitation in the reaction center (RC), possibly due to charge recombination between P(800) (+) and A(0) (-).
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Affiliation(s)
- Aaron M Collins
- Departments of Biology and Chemistry, Washington University in St. Louis, MO 63130, USA
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Baymann F, Nitschke W. Heliobacterial Rieske/cytb complex. PHOTOSYNTHESIS RESEARCH 2010; 104:177-187. [PMID: 20091229 DOI: 10.1007/s11120-009-9524-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2009] [Accepted: 12/21/2009] [Indexed: 05/28/2023]
Abstract
Data on structure and function of the Rieske/cytb complex from Heliobacteria are scarce. They indicate that the complex is related to the b (6) f complex in agreement with the phylogenetic position of the organism. It is composed of a diheme cytochrome c, and a Rieske iron-sulfur protein, together with transmembrane cytochrome b (6) and subunit IV. Additional small subunits may be part of the complex. The cofactor content comprises heme c (i), first discovered in the Q(i) binding pocket of b (6) f complexes. The redox midpoint potentials are more negative than in b (6) f complex in agreement with the lower redox midpoint potentials (by about 150 mV) of its reaction partners, menaquinone, and cytochrome c (553). The enzyme is implicated in cyclic electron transfer around the RCI. Functional studies are favored by the absence of antennae and the simple photosynthetic reaction chain but are hampered by the high oxygen sensitivity of the organism, its chlorophyll, and lipids.
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Affiliation(s)
- F Baymann
- BIP, Centre National de la Recherche Scientifique, UPR9036, IFR88, 31 Chemin Joseph Aiguier, Marseille, France.
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Nitschke W, van Lis R, Schoepp-Cothenet B, Baymann F. The "green" phylogenetic clade of Rieske/cytb complexes. PHOTOSYNTHESIS RESEARCH 2010; 104:347-355. [PMID: 20130997 DOI: 10.1007/s11120-010-9532-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/16/2009] [Accepted: 01/16/2010] [Indexed: 05/28/2023]
Abstract
More than a decade ago, Heliobacteria were recognised to contain a Rieske/cytb complex in which the cytochrome b subunit is split into two separate proteins, a peculiar feature characteristic of the cyanobacterial and plastidic b (6) f complex. The common presence of RCI-type reaction centres further emphasise possible evolutionary links between Heliobacteria, Chlorobiaceae and Cyanobacteria. In this contribution, we further explore the evolutionary relationships among these three phototrophic lineages by both molecular phylogeny and consideration of phylogenetic marker traits of the superfamily of Rieske/cytb complexes. The combination of these two methods suggests the existence of a "green" clade involving many non-phototrophs in addition to the mentioned RCI-type photosynthetic organisms. Structural and functional idiosyncrasies are (re-)interpreted in the framework of evolutionary biology and more specifically evolutionary bioenergetics.
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Affiliation(s)
- W Nitschke
- BIP, Centre National de la Recherche Scientifique, UPR9036, IFR88, 31 Chemin Joseph Aiguier, Marseille, France.
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Sattley WM, Blankenship RE. Insights into heliobacterial photosynthesis and physiology from the genome of Heliobacterium modesticaldum. PHOTOSYNTHESIS RESEARCH 2010; 104:113-122. [PMID: 20130998 DOI: 10.1007/s11120-010-9529-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Accepted: 01/16/2010] [Indexed: 05/28/2023]
Abstract
The complete annotated genome sequence of Heliobacterium modesticaldum strain Ice1 provides our first glimpse into the genetic potential of the Heliobacteriaceae, a unique family of anoxygenic phototrophic bacteria. H. modesticaldum str. Ice1 is the first completely sequenced phototrophic representative of the Firmicutes, and heliobacteria are the only phototrophic members of this large bacterial phylum. The H. modesticaldum genome consists of a single 3.1-Mb circular chromosome with no plasmids. Of special interest are genomic features that lend insight to the physiology and ecology of heliobacteria, including the genetic inventory of the photosynthesis gene cluster. Genes involved in transport, photosynthesis, and central intermediary metabolism are described and catalogued. The obligately heterotrophic metabolism of heliobacteria is a key feature of the physiology and evolution of these phototrophs. The conspicuous absence of recognizable genes encoding the enzyme ATP-citrate lyase prevents autotrophic growth via the reverse citric acid cycle in heliobacteria, thus being a distinguishing differential characteristic between heliobacteria and green sulfur bacteria. The identities of electron carriers that enable energy conservation by cyclic light-driven electron transfer remain in question.
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Affiliation(s)
- W Matthew Sattley
- Department of Biology, MidAmerica Nazarene University, 2030 E. College Way, Olathe, KS 66062, USA
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Baniulis D, Yamashita E, Zhang H, Hasan SS, Cramer WA. Structure-function of the cytochrome b6f complex. Photochem Photobiol 2009; 84:1349-58. [PMID: 19067956 DOI: 10.1111/j.1751-1097.2008.00444.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The structure and function of the cytochrome b6f complex is considered in the context of recent crystal structures of the complex as an eight subunit, 220 kDa symmetric dimeric complex obtained from the thermophilic cyanobacterium, Mastigocladus laminosus, and the green alga, Chlamydomonas reinhardtii. A major problem confronted in crystallization of the cyanobacterial complex, proteolysis of three of the subunits, is discussed along with initial efforts to identify the protease. The evolution of these cytochrome complexes is illustrated by conservation of the hydrophobic heme-binding transmembrane domain of the cyt b polypeptide between b6f and bc1 complexes, and the rubredoxin-like membrane proximal domain of the Rieske [2Fe-2S] protein. Pathways of coupled electron and proton transfer are discussed in the framework of a modified Q cycle, in which the heme c(n), not found in the bc1 complex, but electronically tightly coupled to the heme b(n) of the b6f complex, is included. Crystal structures of the cyanobacterial complex with the quinone analogue inhibitors, NQNO or tridecyl-stigmatellin, show the latter to be ligands of heme c(n), implicating heme c(n) as an n-side plastoquinone reductase. Existing questions include (a) the details of the shuttle of: (i) the [2Fe-2S] protein between the membrane-bound PQH2 electron/H+ donor and the cytochrome f acceptor to complete the p-side electron transfer circuit; (ii) PQ/PQH2 between n- and p-sides of the complex across the intermonomer quinone exchange cavity, through the narrow portal connecting the cavity with the p-side [2Fe-2S] niche; (b) the role of the n-side of the b6f complex and heme c(n) in regulation of the relative rates of noncyclic and cyclic electron transfer. The likely presence of cyclic electron transport in the b6f complex, and of heme c(n) in the firmicute bc complex suggests the concept that hemes b(n)-c(n) define a branch point in bc complexes that can support electron transport pathways that differ in detail from the Q cycle supported by the bc1 complex.
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Affiliation(s)
- D Baniulis
- Department of Biological Sciences, Purdue University, West Lafayette, IN, USA
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Ducluzeau A, Chenu E, Capowiez L, Baymann F. The Rieske/cytochrome b complex of Heliobacteria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1777:1140-6. [DOI: 10.1016/j.bbabio.2008.04.026] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Revised: 03/28/2008] [Accepted: 04/15/2008] [Indexed: 11/27/2022]
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Bailleul B, Johnson X, Finazzi G, Barber J, Rappaport F, Telfer A. The Thermodynamics and Kinetics of Electron Transfer between Cytochrome b6f and Photosystem I in the Chlorophyll d-dominated Cyanobacterium, Acaryochloris marina. J Biol Chem 2008; 283:25218-25226. [DOI: 10.1074/jbc.m803047200] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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The genome of Heliobacterium modesticaldum, a phototrophic representative of the Firmicutes containing the simplest photosynthetic apparatus. J Bacteriol 2008; 190:4687-96. [PMID: 18441057 DOI: 10.1128/jb.00299-08] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Despite the fact that heliobacteria are the only phototrophic representatives of the bacterial phylum Firmicutes, genomic analyses of these organisms have yet to be reported. Here we describe the complete sequence and analysis of the genome of Heliobacterium modesticaldum, a thermophilic species belonging to this unique group of phototrophs. The genome is a single 3.1-Mb circular chromosome containing 3,138 open reading frames. As suspected from physiological studies of heliobacteria that have failed to show photoautotrophic growth, genes encoding enzymes for known autotrophic pathways in other phototrophic organisms, including ribulose bisphosphate carboxylase (Calvin cycle), citrate lyase (reverse citric acid cycle), and malyl coenzyme A lyase (3-hydroxypropionate pathway), are not present in the H. modesticaldum genome. Thus, heliobacteria appear to be the only known anaerobic anoxygenic phototrophs that are not capable of autotrophy. Although for some cellular activities, such as nitrogen fixation, there is a full complement of genes in H. modesticaldum, other processes, including carbon metabolism and endosporulation, are more genetically streamlined than they are in most other low-G+C gram-positive bacteria. Moreover, several genes encoding photosynthetic functions in phototrophic purple bacteria are not present in the heliobacteria. In contrast to the nutritional flexibility of many anoxygenic phototrophs, the complete genome sequence of H. modesticaldum reveals an organism with a notable degree of metabolic specialization and genomic reduction.
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Abstract
The reaction center (RC) of heliobacteria contains iron-sulfur centers as terminal electron acceptors, analogous to those of green sulfur bacteria as well as photosystem I in cyanobacteria and higher plants. Therefore, they all belong to the so-called type 1 RCs, in contrast to the type 2 RCs of purple bacteria and photosystem II containing quinone molecules. Although the architecture of the heliobacterial RC as a protein complex is still unknown, it forms a homodimer made up of two identical PshA core proteins, where two symmetrical electron transfer pathways along the C2 axis are assumed to be equally functional. Electrons are considered to be transferred from membrane-bound cytochrome c (PetJ) to a special pair P800, a chlorophyll a-like molecule A0, (a quinone molecule A1) and a [4Fe-4S] center Fx and, finally, to 2[4Fe-4S] centers FA/FB. No definite evidence has been obtained for the presence of functional quinone acceptor A1. An additional interesting point is that the electron transfer reaction from cytochrome c to P800 proceeds in a collisional mode. It is highly dependent on the temperature, ion strength and/or viscosity in a reaction medium, suggesting that a heme-binding moiety fluctuates in an aqueous phase with its amino-terminus anchored to membranes.
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Affiliation(s)
- Hirozo Oh-oka
- Department of Biological Sciences, Graduate School of Science, Osaka University, Osaka, Japan.
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Heinnickel M, Golbeck JH. Heliobacterial photosynthesis. PHOTOSYNTHESIS RESEARCH 2007; 92:35-53. [PMID: 17457690 DOI: 10.1007/s11120-007-9162-4] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Accepted: 03/23/2007] [Indexed: 05/15/2023]
Abstract
Heliobacteria contain Type I reaction centers (RCs) and a homodimeric core, but unlike green sulfur bacteria, they do not contain an extended antenna system. Given their simplicity, the heliobacterial RC (HbRC) should be ideal for the study of a prototypical homodimeric RC. However, there exist enormous gaps in our knowledge, particularly with regard to the nature of the secondary and tertiary electron acceptors. To paraphrase S. Neerken and J. Amesz (2001 Biochim Biophys Acta 1507:278-290): with the sole exception of primary charge separation, little progress has been made in recent years on the HbRC, either with respect to the polypeptide composition, or the nature of the electron acceptor chain, or the kinetics of forward and backward electron transfer. This situation, however, has changed. First, the low molecular mass polypeptide that contains the terminal FA and FB iron-sulfur clusters has been identified. The change in the lifetime of the flash-induced kinetics from 75 ms to 15 ms on its removal shows that the former arises from the P798+ [FA/FB]- recombination, and the latter from P798+ FX- recombination. Second, FX has been identified in HbRC cores by EPR and Mössbauer spectroscopy, and shown to be a [4Fe-4S]1+,2+ cluster with a ground spin state of S=3/2. Since all of the iron in HbRC cores is in the FX cluster, a ratio of approximately 22 Bchl g/P798 could be calculated from chemical assays of non-heme iron and Bchl g. Third, the N-terminal amino acid sequence of the FA/FB-containing polypeptide led to the identification and cloning of its gene. The expressed protein can be rebound to isolated HbRC cores, thereby regaining both the 75 ms kinetic phase resulting from P798+ [FA/FB]- recombination and the light-induced EPR resonances of FA- and FB-. The gene was named 'pshB' and the protein 'PshB' in keeping with the accepted nomenclature for Type I RCs. This article reviews the current state of knowledge on the structure and function of the HbRC.
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Affiliation(s)
- Mark Heinnickel
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA
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Cape JL, Strahan JR, Lenaeus MJ, Yuknis BA, Le TT, Shepherd JN, Bowman MK, Kramer DM. The respiratory substrate rhodoquinol induces Q-cycle bypass reactions in the yeast cytochrome bc(1) complex: mechanistic and physiological implications. J Biol Chem 2005; 280:34654-60. [PMID: 16087663 DOI: 10.1074/jbc.m507616200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial cytochrome bc(1) complex catalyzes the transfer of electrons from ubiquinol to cyt c while generating a proton motive force for ATP synthesis via the "Q-cycle" mechanism. Under certain conditions electron flow through the Q-cycle is blocked at the level of a reactive intermediate in the quinol oxidase site of the enzyme, resulting in "bypass reactions," some of which lead to superoxide production. Using analogs of the respiratory substrates ubiquinol-3 and rhodoquinol-3, we show that the relative rates of Q-cycle bypass reactions in the Saccharomyces cerevisiae cyt bc(1) complex are highly dependent by a factor of up to 100-fold on the properties of the substrate quinol. Our results suggest that the rate of Q-cycle bypass reactions is dependent on the steady state concentration of reactive intermediates produced at the quinol oxidase site of the enzyme. We conclude that normal operation of the Q-cycle requires a fairly narrow window of redox potentials with respect to the quinol substrate to allow normal turnover of the complex while preventing potentially damaging bypass reactions.
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Affiliation(s)
- Jonathan L Cape
- Institute of Biological Chemistry, Washingston State University, Pullman, Washington 99164-6340, USA
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23
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Schneider D, Skrzypczak S, Anemüller S, Schmidt CL, Seidler A, Rögner M. Heterogeneous Rieske proteins in the cytochrome b6f complex of Synechocystis PCC6803? J Biol Chem 2002; 277:10949-54. [PMID: 11788579 DOI: 10.1074/jbc.m104076200] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The completely sequenced genome of the cyanobacterium Synechocystis PCC6803 contains three open reading frames, petC1, petC2, and petC3, encoding putative Rieske iron-sulfur proteins. After heterologous overexpression, all three gene products have been characterized and shown to be Rieske proteins as typified by sequence analysis and EPR spectroscopy. Two of the overproduced proteins contained already incorporated iron-sulfur clusters, whereas the third one formed unstable aggregates, in which the FeS cluster had to be reconstituted after refolding of the denatured protein. Although EPR spectroscopy showed typical FeS signals for all Rieske proteins, an unusual low midpoint potential was revealed for PetC3 by EPR redox titration. Detailed characterization of Synechocystis membranes indicated that all three Rieske proteins are expressed under physiological conditions. Both for PetC1 and PetC3 the association with the thylakoid membrane was shown, and both could be identified, although in different amounts, in the isolated cytochrome b(6)f complex. The considerably lower redox potential determined for PetC3 indicates heterogeneous cytochrome b(6)f complexes in Synechocystis and suggests still to be established alternative electron transport routes.
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Affiliation(s)
- Dirk Schneider
- Lehrstuhl für Biochemie der Pflanzen, Fakultät für Biologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
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Neerken S, Amesz J. The antenna reaction center complex of heliobacteria: composition, energy conversion and electron transfer. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1507:278-90. [PMID: 11687220 DOI: 10.1016/s0005-2728(01)00207-9] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
A survey is given of various aspects of the photosynthetic processes in heliobacteria. The review mainly refers to results obtained since 1995, which had not been covered earlier. It first discusses the antenna organization and pigmentation. The pigments of heliobacteria include some unusual species: bacteriochlorophyll (BChl) g, the main pigment, 8(1) hydroxy chlorophyll a, which acts as primary electron acceptor, and 4,4'-diaponeurosporene, a carotenoid with 30 carbon atoms. Energy conversion within the antenna is very fast: at room temperature thermal equilibrium among the approx. 35 BChls g of the antenna is largely completed within a few ps. This is then followed by primary charge separation, involving a dimer of BChl g (P798) as donor, but recent evidence indicates that excitation of the acceptor pigment 8(1) hydroxy chlorophyll a gives rise to an alternative primary reaction not involving excited P798. The final section of the review concerns secondary electron transfer, an area that is relatively poorly known in heliobacteria.
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Affiliation(s)
- S Neerken
- Department of Biophysics, Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.
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25
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Schütz M, Brugna M, Lebrun E, Baymann F, Huber R, Stetter KO, Hauska G, Toci R, Lemesle-Meunier D, Tron P, Schmidt C, Nitschke W. Early evolution of cytochrome bc complexes. J Mol Biol 2000; 300:663-75. [PMID: 10891261 DOI: 10.1006/jmbi.2000.3915] [Citation(s) in RCA: 135] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Primary structures, functional characteristics and phylogenetic relationships of subunits of cytochrome bc complexes from phylogenetically diverse bacterial and archaeal species were analysed. A single case of lateral gene transfer, i.e. the import of an epsilon-proteobacterial cytochrome bc(1) complex into Aquificales, was identified. For the enzyme in the remainder of the species studied, the obtained phylogenies were globally in line with small subunit rRNA trees. The distribution of a few key phylogenetic markers, such as contiguousness of cytochrome b, nature of the c-type subunit or spacing between b-heme ligands, are discussed. A localised modification of previous tree topologies is proposed on the basis of the obtained data. The comparison of extant enzymes furthermore allowed us to define the minimal functional and evolutionary core of the enzyme. The data furthermore suggest that the ancestral enzyme was put together from subunits that previously had played a role in other electron transfer chains.
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Affiliation(s)
- M Schütz
- Laboratoire de Bioénergétique et Ingénierie des Protéines (UPR 9036, France
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26
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Brugna M, Nitschke W, Asso M, Guigliarelli B, Lemesle-Meunier D, Schmidt C. Redox components of cytochrome bc-type enzymes in acidophilic prokaryotes. II. The Rieske protein of phylogenetically distant acidophilic organisms. J Biol Chem 1999; 274:16766-72. [PMID: 10358018 DOI: 10.1074/jbc.274.24.16766] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Rieske proteins of two phylogenetically distant acidophilic organisms, i.e. the proteobacterium Thiobacillus ferrooxidans and the crenarchaeon Sulfolobus acidocaldarius, were studied by EPR. Redox titrations at a range of pH values showed that the Rieske centers of both organisms are characterized by redox midpoint potential-versus-pH curves featuring a common pK value of 6.2. This pK value is significantly more acidic (by almost 2 pH units) than that of Rieske proteins in neutrophilic species. The orientations of the Rieske center's g tensors with respect to the plane of the membrane were studied between pH 4 and 8 using partially ordered samples. At pH 4, the Sulfolobus Rieske cluster was found in the "typical" orientation of chemically reduced Rieske centers, whereas this orientation changed significantly on going toward high pH values. The Thiobacillus protein, by contrast, appeared to be in the "standard" orientation at both low and high pH values. The results are discussed with respect to the molecular parameters conveying acid resistance and in light of the recently demonstrated long-range conformational movement of the Rieske protein during enzyme turnover in cytochrome bc1 complexes.
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Affiliation(s)
- M Brugna
- Laboratoire de Bioénergétique et Ingénierie des Protéines (UPR 9036), CNRS, Institut de Biologie Structurale et Microbiologie, 31 chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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27
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Xiong J, Inoue K, Bauer CE. Tracking molecular evolution of photosynthesis by characterization of a major photosynthesis gene cluster from Heliobacillus mobilis. Proc Natl Acad Sci U S A 1998; 95:14851-6. [PMID: 9843979 PMCID: PMC24539 DOI: 10.1073/pnas.95.25.14851] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/1998] [Accepted: 10/13/1998] [Indexed: 11/18/2022] Open
Abstract
A DNA sequence has been obtained for a 35.6-kb genomic segment from Heliobacillus mobilis that contains a major cluster of photosynthesis genes. A total of 30 ORFs were identified, 20 of which encode enzymes for bacteriochlorophyll and carotenoid biosynthesis, reaction-center (RC) apoprotein, and cytochromes for cyclic electron transport. Donor side electron-transfer components to the RC include a putative RC-associated cytochrome c553 and a unique four-large-subunit cytochrome bc complex consisting of Rieske Fe-S protein (encoded by petC), cytochrome b6 (petB), subunit IV (petD), and a diheme cytochrome c (petX). Phylogenetic analysis of various photosynthesis gene products indicates a consistent grouping of oxygenic lineages that are distinct and descendent from anoxygenic lineages. In addition, H. mobilis was placed as the closest relative to cyanobacteria, which form a monophyletic origin to chloroplast-based photosynthetic lineages. The consensus of the photosynthesis gene trees also indicates that purple bacteria are the earliest emerging photosynthetic lineage. Our analysis also indicates that an ancient gene-duplication event giving rise to the paralogous bchI and bchD genes predates the divergence of all photosynthetic groups. In addition, our analysis of gene duplication of the photosystem I and photosystem II core polypeptides supports a "heterologous fusion model" for the origin and evolution of oxygenic photosynthesis.
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Affiliation(s)
- J Xiong
- Department of Biology, Indiana University, Bloomington, IN 47405, USA
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28
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Abstract
The aerobic anoxygenic phototrophic bacteria are a relatively recently discovered bacterial group. Although taxonomically and phylogenetically heterogeneous, these bacteria share the following distinguishing features: the presence of bacteriochlorophyll a incorporated into reaction center and light-harvesting complexes, low levels of the photosynthetic unit in cells, an abundance of carotenoids, a strong inhibition by light of bacteriochlorophyll synthesis, and the inability to grow photosynthetically under anaerobic conditions. Aerobic anoxygenic phototrophic bacteria are classified in two marine (Erythrobacter and Roseobacter) and six freshwater (Acidiphilium, Erythromicrobium, Erythromonas, Porphyrobacter, Roseococcus, and Sandaracinobacter) genera, which phylogenetically belong to the alpha-1, alpha-3, and alpha-4 subclasses of the class Proteobacteria. Despite this phylogenetic information, the evolution and ancestry of their photosynthetic properties are unclear. We discuss several current proposals for the evolutionary origin of aerobic phototrophic bacteria. The closest phylogenetic relatives of aerobic phototrophic bacteria include facultatively anaerobic purple nonsulfur phototrophic bacteria. Since these two bacterial groups share many properties, yet have significant differences, we compare and contrast their physiology, with an emphasis on morphology and photosynthetic and other metabolic processes.
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Affiliation(s)
- V V Yurkov
- Department of Microbiology and Immunology, The University of British Columbia, Vancouver, Canada V6T 1Z3.
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29
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Brugna M, Albouy D, Nitschke W. Diversity of cytochrome bc complexes: example of the Rieske protein in green sulfur bacteria. J Bacteriol 1998; 180:3719-23. [PMID: 9658021 PMCID: PMC107346 DOI: 10.1128/jb.180.14.3719-3723.1998] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/1998] [Accepted: 05/17/1998] [Indexed: 02/08/2023] Open
Abstract
The Rieske 2Fe2S cluster of Chlorobium limicola forma thiosulfatophilum strain tassajara was studied by electron paramagnetic resonance spectroscopy. Two distinct orientations of its g tensor were observed in oriented samples corresponding to differing conformations of the protein. Only one of the two conformations persisted after treatment with 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone. A redox midpoint potential (Em) of +160 mV in the pH range of 6 to 7.7 and a decreasing Em (-60 to -80 mV/pH unit) above pH 7.7 were found. The implications of the existence of differing conformational states of the Rieske protein, as well as of the shape of its Em-versus-pH curve, in green sulfur bacteria are discussed.
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Affiliation(s)
- M Brugna
- Laboratoire de Bioénergétique et Ingénierie des Protéines (UPR 9036), Institut de Biologie Structurale et Microbiologie, 13402 Marseille Cedex 20, France
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30
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Brettel K, Leibl W, Liebl U. Electron transfer in the heliobacterial reaction center: evidence against a quinone-type electron acceptor functioning analogous to A1 in photosystem I. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1363:175-81. [PMID: 9518598 DOI: 10.1016/s0005-2728(98)00010-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Membrane fragments from Heliobacillus mobilis were characterized using time resolved optical spectroscopy and photovoltage measurements in order to detect a possible participation of menaquinone (MQ), functioning analogous to the phylloquinone A1 in photosystem I, as intermediate in electron transfer from the primary acceptor A0 to the iron-sulfur cluster FX in the photosynthetic reaction center. The spectroscopic data obtained exclude that electron transfer from a semiquinone anion MQ- to FX occurred in the time window from 2 ns to 4 micros, where it would be expected in analogy to photosystem I. In the case of a prereduction of FX, only the primary pair P798+A0- was formed. The photovoltage data yielded a single kinetic phase with a time constant of 700 ps for the transmembrane electron transfer beyond A0; the relative amplitude of this phase suggests that it reflects electron transfer from A0- to FX.
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Affiliation(s)
- K Brettel
- Section de Bioénergétique, DBCM, CEA and CNRS URA 2096, Centre d'Etudes de Saclay, 91191 Gif-sur-Yvette Cedex, France.
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31
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Albouy D, Joliot P, Robert B, Nitschke W. Electron transfer towards the RCI-type photosystem in the green sulphur bacterium Chlorobium limicola forma thiosulphatophilum studied by time-resolved optical spectroscopy in vivo. EUROPEAN JOURNAL OF BIOCHEMISTRY 1997; 249:630-6. [PMID: 9370376 DOI: 10.1111/j.1432-1033.1997.t01-2-00630.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Flash-induced spectral changes in the wavelength region of the alpha-peaks of heme proteins and in the time domain from microseconds to seconds have been recorded on whole cells of the green sulphur bacterium Chlorobium limicola forma thiosulfatophilum. Extensive flash-excitation by trains of flashes resulted in oxidation of 7-8 c-type heme molecules/photosynthetic reaction centre. The complement of heme species was found to be spectrally heterogeneous allowing the study of electron transfer events induced by an isolated single-turnover flash. Under single-flash conditions, a c553 heme was seen to become oxidised with tau = 30 micros, concommitant with the reduction of the primary donor of the reaction centre. Subsequently, the alpha-peak of the photooxidised heme broadened and shifted towards longer wavelengths (tau = 70 micros) indicating equilibration of the positive charge over two differing heme species. In the time domain t > 1 ms, rereduction of c-type hemes was seen to be paralleled by a blue shift and further broadening of the alpha-peak. Concommitantly, b-type hemes were observed to first become reduced (within a few milliseconds), then over-oxidised (t > 200 ms) and eventually rereduced to their redox state prior to the flash. The results obtained are discussed with respect to the question of the identity of the immediate electron donor to the photosynthetic reaction centre and with respect to the involvement of a cytochrome bc complex in photo-induced electron transport of green sulphur bacteria.
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Affiliation(s)
- D Albouy
- Institut de Biologie Physico-Chimique, Service de Photosynthèse, Paris, France
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