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Rolando JL, Kolton M, Song T, Liu Y, Pinamang P, Conrad R, Morris JT, Konstantinidis KT, Kostka JE. Sulfur oxidation and reduction are coupled to nitrogen fixation in the roots of the salt marsh foundation plant Spartina alterniflora. Nat Commun 2024; 15:3607. [PMID: 38684658 PMCID: PMC11059160 DOI: 10.1038/s41467-024-47646-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 04/09/2024] [Indexed: 05/02/2024] Open
Abstract
Heterotrophic activity, primarily driven by sulfate-reducing prokaryotes, has traditionally been linked to nitrogen fixation in the root zone of coastal marine plants, leaving the role of chemolithoautotrophy in this process unexplored. Here, we show that sulfur oxidation coupled to nitrogen fixation is a previously overlooked process providing nitrogen to coastal marine macrophytes. In this study, we recovered 239 metagenome-assembled genomes from a salt marsh dominated by the foundation plant Spartina alterniflora, including diazotrophic sulfate-reducing and sulfur-oxidizing bacteria. Abundant sulfur-oxidizing bacteria encode and highly express genes for carbon fixation (RuBisCO), nitrogen fixation (nifHDK) and sulfur oxidation (oxidative-dsrAB), especially in roots stressed by sulfidic and reduced sediment conditions. Stressed roots exhibited the highest rates of nitrogen fixation and expression level of sulfur oxidation and sulfate reduction genes. Close relatives of marine symbionts from the Candidatus Thiodiazotropha genus contributed ~30% and ~20% of all sulfur-oxidizing dsrA and nitrogen-fixing nifK transcripts in stressed roots, respectively. Based on these findings, we propose that the symbiosis between S. alterniflora and sulfur-oxidizing bacteria is key to ecosystem functioning of coastal salt marshes.
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Affiliation(s)
- J L Rolando
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
| | - M Kolton
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
- French Associates Institute for Agriculture and Biotechnology of Drylands, Ben-Gurion University of the Negev, Beer Sheva, Israel
| | - T Song
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
| | - Y Liu
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
- The Pennsylvania State University, Department of Civil & Environmental Engineering, University Park, PA, 16802, USA
| | - P Pinamang
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
| | - R Conrad
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
| | - J T Morris
- Belle Baruch Institute for Marine & Coastal Sciences, University of South Carolina, Columbia, SC, 29201, USA
| | - K T Konstantinidis
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA
- Georgia Institute of Technology, School of Civil and Environmental Engineering, Atlanta, GA, 30332, USA
| | - J E Kostka
- Georgia Institute of Technology, School of Biological Sciences, Atlanta, GA, 30332, USA.
- Georgia Institute of Technology, School of Earth and Atmospheric Sciences, Atlanta, GA, 30332, USA.
- Center for Microbial Dynamics and Infection, Georgia Institute of Technology, Atlanta, GA, 30332, USA.
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Petushkova E, Khasimov M, Mayorova E, Delegan Y, Frantsuzova E, Bogun A, Galkina E, Tsygankov A. The Complete Genome of a Novel Typical Species Thiocapsa bogorovii and Analysis of Its Central Metabolic Pathways. Microorganisms 2024; 12:391. [PMID: 38399794 PMCID: PMC10892978 DOI: 10.3390/microorganisms12020391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2024] [Revised: 02/08/2024] [Accepted: 02/10/2024] [Indexed: 02/25/2024] Open
Abstract
The purple sulfur bacterium Thiocapsa roseopersicina BBS is interesting from both fundamental and practical points of view. It possesses a thermostable HydSL hydrogenase, which is involved in the reaction of reversible hydrogen activation and a unique reaction of sulfur reduction to hydrogen sulfide. It is a very promising enzyme for enzymatic hydrogenase electrodes. There are speculations that HydSL hydrogenase of purple bacteria is closely related to sulfur metabolism, but confirmation is required. For that, the full genome sequence is necessary. Here, we sequenced and assembled the complete genome of this bacterium. The analysis of the obtained whole genome, through an integrative approach that comprised estimating the Average Nucleotide Identity (ANI) and digital DNA-DNA hybridization (DDH) parameters, allowed for validation of the systematic position of T. roseopersicina as T. bogorovii BBS. For the first time, we have assembled the whole genome of this typical strain of a new bacterial species and carried out its functional description against another purple sulfur bacterium: Allochromatium vinosum DSM 180T. We refined the automatic annotation of the whole genome of the bacteria T. bogorovii BBS and localized the genomic positions of several studied genes, including those involved in sulfur metabolism and genes encoding the enzymes required for the TCA and glyoxylate cycles and other central metabolic pathways. Eleven additional genes coding proteins involved in pigment biosynthesis was found.
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Affiliation(s)
- Ekaterina Petushkova
- Institute of Basic Biological Problems, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (M.K.); (E.M.); (A.T.)
| | - Makhmadyusuf Khasimov
- Institute of Basic Biological Problems, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (M.K.); (E.M.); (A.T.)
| | - Ekaterina Mayorova
- Institute of Basic Biological Problems, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (M.K.); (E.M.); (A.T.)
| | - Yanina Delegan
- Institute of Biochemistry and Physiology of Microorganisms, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (Y.D.); (E.F.); (A.B.)
| | - Ekaterina Frantsuzova
- Institute of Biochemistry and Physiology of Microorganisms, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (Y.D.); (E.F.); (A.B.)
| | - Alexander Bogun
- Institute of Biochemistry and Physiology of Microorganisms, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (Y.D.); (E.F.); (A.B.)
| | - Elena Galkina
- State Research Center for Applied Microbiology and Biotechnology, 142279 Obolensk, Moscow Region, Russia;
| | - Anatoly Tsygankov
- Institute of Basic Biological Problems, Federal Research Center “Pushchino Scientific Center for Biological Research of Russian Academy of Sciences” (FRC PSCBR RAS), 142290 Pushchino, Moscow Region, Russia; (M.K.); (E.M.); (A.T.)
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3
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Sattley WM, Swingley WD, Burchell BM, Dewey ED, Hayward MK, Renbarger TL, Shaffer KN, Stokes LM, Gurbani SA, Kujawa CM, Nuccio DA, Schladweiler J, Touchman JW, Wang-Otomo ZY, Blankenship RE, Madigan MT. Complete genome of the thermophilic purple sulfur Bacterium Thermochromatium tepidum compared to Allochromatium vinosum and other Chromatiaceae. PHOTOSYNTHESIS RESEARCH 2022; 151:125-142. [PMID: 34669148 DOI: 10.1007/s11120-021-00870-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Accepted: 08/07/2021] [Indexed: 06/13/2023]
Abstract
The complete genome sequence of the thermophilic purple sulfur bacterium Thermochromatium tepidum strain MCT (DSM 3771T) is described and contrasted with that of its mesophilic relative Allochromatium vinosum strain D (DSM 180T) and other Chromatiaceae. The Tch. tepidum genome is a single circular chromosome of 2,958,290 base pairs with no plasmids and is substantially smaller than the genome of Alc. vinosum. The Tch. tepidum genome encodes two forms of RuBisCO and contains nifHDK and several other genes encoding a molybdenum nitrogenase but lacks a gene encoding a protein that assembles the Fe-S cluster required to form a functional nitrogenase molybdenum-iron cofactor, leaving the phototroph phenotypically Nif-. Tch. tepidum contains genes necessary for oxidizing sulfide to sulfate as photosynthetic electron donor but is genetically unequipped to either oxidize thiosulfate as an electron donor or carry out assimilative sulfate reduction, both of which are physiological hallmarks of Alc. vinosum. Also unlike Alc. vinosum, Tch. tepidum is obligately phototrophic and unable to grow chemotrophically in darkness by respiration. Several genes present in the Alc. vinosum genome that are absent from the genome of Tch. tepidum likely contribute to the major physiological differences observed between these related purple sulfur bacteria that inhabit distinct ecological niches.
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Affiliation(s)
- W Matthew Sattley
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA.
| | - Wesley D Swingley
- Department of Biological Sciences, Northern Illinois University, Dekalb, IL, 60115, USA
| | - Brad M Burchell
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Emma D Dewey
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Mackenzie K Hayward
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Tara L Renbarger
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Kathryn N Shaffer
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Lynn M Stokes
- Division of Natural Sciences, Indiana Wesleyan University, Marion, IN, 46953, USA
| | - Sonja A Gurbani
- Department of Biological Sciences, Northern Illinois University, Dekalb, IL, 60115, USA
| | - Catrina M Kujawa
- Department of Biological Sciences, Northern Illinois University, Dekalb, IL, 60115, USA
| | - D Adam Nuccio
- Department of Biological Sciences, Northern Illinois University, Dekalb, IL, 60115, USA
| | - Jacob Schladweiler
- Department of Biological Sciences, Northern Illinois University, Dekalb, IL, 60115, USA
| | - Jeffrey W Touchman
- School of Life Sciences, Arizona State University, Tempe, AR, 85287, USA
| | | | - Robert E Blankenship
- Departments of Chemistry and Biology, Washington University, St. Louis, MO, 63130, USA
| | - Michael T Madigan
- Department of Microbiology, School of Biological Sciences, Southern Illinois University, Carbondale, IL, 62901, USA
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Duarte AG, Barbosa ACC, Ferreira D, Manteigas G, Domingos RM, Pereira IAC. Redox loops in anaerobic respiration - The role of the widespread NrfD protein family and associated dimeric redox module. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2021; 1862:148416. [PMID: 33753023 DOI: 10.1016/j.bbabio.2021.148416] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 02/25/2021] [Accepted: 03/11/2021] [Indexed: 02/06/2023]
Abstract
In prokaryotes, the proton or sodium motive force required for ATP synthesis is produced by respiratory complexes that present an ion-pumping mechanism or are involved in redox loops performed by membrane proteins that usually have substrate and quinone-binding sites on opposite sides of the membrane. Some respiratory complexes include a dimeric redox module composed of a quinone-interacting membrane protein of the NrfD family and an iron‑sulfur protein of the NrfC family. The QrcABCD complex of sulfate reducers, which includes the QrcCD module homologous to NrfCD, was recently shown to perform electrogenic quinone reduction providing the first conclusive evidence for energy conservation among this family. Similar redox modules are present in multiple respiratory complexes, which can be associated with electroneutral, energy-driven or electrogenic reactions. This work discusses the presence of the NrfCD/PsrBC dimeric redox module in different bioenergetics contexts and its role in prokaryotic energy conservation mechanisms.
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Affiliation(s)
- Américo G Duarte
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal.
| | - Ana C C Barbosa
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal
| | - Delfim Ferreira
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal
| | - Gonçalo Manteigas
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal
| | - Renato M Domingos
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal
| | - Inês A C Pereira
- Instituto de Tecnologia Química e Biológica António Xavier/Universidade Nova de Lisboa, Av. da República, Estação Agronómica Nacional, 2780-157 Oeiras, Portugal.
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5
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Lim SJ, Alexander L, Engel AS, Paterson AT, Anderson LC, Campbell BJ. Extensive Thioautotrophic Gill Endosymbiont Diversity within a Single Ctena orbiculata (Bivalvia: Lucinidae) Population and Implications for Defining Host-Symbiont Specificity and Species Recognition. mSystems 2019; 4:e00280-19. [PMID: 31455638 PMCID: PMC6712303 DOI: 10.1128/msystems.00280-19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2019] [Accepted: 08/06/2019] [Indexed: 11/20/2022] Open
Abstract
Seagrass-dwelling members of the bivalve family Lucinidae harbor environmentally acquired gill endosymbionts. According to previous studies, lucinid symbionts potentially represent multiple strains from a single thioautotrophic gammaproteobacterium species. This study utilized genomic- and transcriptomic-level data to resolve symbiont taxonomic, genetic, and functional diversity from Ctena orbiculata endosymbiont populations inhabiting carbonate-rich sediment at Sugarloaf Key, FL (USA). The sediment had mixed seagrass and calcareous green alga coverage and also was colonized by at least five other lucinid species. Four coexisting, thioautotrophic endosymbiont operational taxonomic units (OTUs), likely representing four strains from two different bacterial species, were identified from C. orbiculata Three of these OTUs also occurred at high relative abundances in the other sympatric lucinid species. Interspecies genetic differences averaged about 5% lower at both pairwise average nucleotide identity and amino acid identity than interstrain differences. Despite these genetic differences, C. orbiculata endosymbionts shared a high number of metabolic functions, including highly expressed thioautotrophy-related genes and a moderately to weakly expressed conserved one-carbon (C1) oxidation gene cluster previously undescribed in lucinid symbionts. Few symbiont- and host-related genes, including those encoding symbiotic sulfurtransferase, host respiratory functions, and host sulfide oxidation functions, were differentially expressed between seagrass- and alga-covered sediment locations. In contrast to previous studies, the identification of multiple endosymbiont taxa within and across C. orbiculata individuals, which were also shared with other sympatric lucinid species, suggests that neither host nor endosymbiont displays strict taxonomic specificity. This necessitates further investigations into the nature and extent of specificity of lucinid hosts and their symbionts.IMPORTANCE Symbiont diversity and host/symbiont functions have been comprehensively profiled for only a few lucinid species. In this work, unprecedented thioautotrophic gill endosymbiont taxonomic diversity was characterized within a Ctena orbiculata population associated with both seagrass- and alga-covered sediments. Endosymbiont metabolisms included known chemosynthetic functions and an additional conserved, previously uncharacterized C1 oxidation pathway. Lucinid-symbiont associations were not species specific because this C. orbiculata population hosted multiple endosymbiont strains and species, and other sympatric lucinid species shared overlapping symbiont 16S rRNA gene diversity profiles with C. orbiculata Our results suggest that lucinid-symbiont association patterns within some host species could be more taxonomically diverse than previously thought. As such, this study highlights the importance of holistic analyses, at the population, community, and even ecosystem levels, in understanding host-microbe association patterns.
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Affiliation(s)
- Shen Jean Lim
- Department of Biological Sciences, Clemson University, Clemson, South Carolina, USA
| | - Louie Alexander
- Department of Biological Sciences, Clemson University, Clemson, South Carolina, USA
| | - Annette Summers Engel
- Department of Earth and Planetary Sciences, University of Tennessee-Knoxville, Knoxville, Tennessee, USA
| | - Audrey T Paterson
- Department of Earth and Planetary Sciences, University of Tennessee-Knoxville, Knoxville, Tennessee, USA
| | - Laurie C Anderson
- Department of Geology and Geological Engineering, South Dakota School of Mines & Technology, Rapid City, South Dakota, USA
| | - Barbara J Campbell
- Department of Biological Sciences, Clemson University, Clemson, South Carolina, USA
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Borisov VB, Forte E, Siletsky SA, Arese M, Davletshin AI, Sarti P, Giuffrè A. Cytochrome bd protects bacteria against oxidative and nitrosative stress: A potential target for next-generation antimicrobial agents. BIOCHEMISTRY (MOSCOW) 2015; 80:565-75. [DOI: 10.1134/s0006297915050077] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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7
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Ravcheev DA, Thiele I. Systematic genomic analysis reveals the complementary aerobic and anaerobic respiration capacities of the human gut microbiota. Front Microbiol 2014; 5:674. [PMID: 25538694 PMCID: PMC4257093 DOI: 10.3389/fmicb.2014.00674] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Accepted: 11/19/2014] [Indexed: 11/13/2022] Open
Abstract
Because of the specific anatomical and physiological properties of the human intestine, a specific oxygen gradient builds up within this organ that influences the intestinal microbiota. The intestinal microbiome has been intensively studied in recent years, and certain respiratory substrates used by gut inhabiting microbes have been shown to play a crucial role in human health. Unfortunately, a systematic analysis has not been previously performed to determine the respiratory capabilities of human gut microbes (HGM). Here, we analyzed the distribution of aerobic and anaerobic respiratory reductases in 254 HGM genomes. In addition to the annotation of known enzymes, we also predicted a novel microaerobic reductase and novel thiosulfate reductase. Based on this comprehensive assessment of respiratory reductases in the HGM, we proposed a number of exchange pathways among different bacteria involved in the reduction of various nitrogen oxides. The results significantly expanded our knowledge of HGM metabolism and interactions in bacterial communities.
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Affiliation(s)
- Dmitry A Ravcheev
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg Esch-sur-Alzette, Luxembourg ; Division 6: Comparative Genomics of Regulation System, A. A. Kharkevich Institute for Information Transmission Problems, Russian Academy of Sciences Moscow, Russia
| | - Ines Thiele
- Luxembourg Centre for Systems Biomedicine, University of Luxembourg Esch-sur-Alzette, Luxembourg
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8
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Weissgerber T, Zigann R, Bruce D, Chang YJ, Detter JC, Han C, Hauser L, Jeffries CD, Land M, Munk AC, Tapia R, Dahl C. Complete genome sequence of Allochromatium vinosum DSM 180(T). Stand Genomic Sci 2011; 5:311-30. [PMID: 22675582 PMCID: PMC3368242 DOI: 10.4056/sigs.2335270] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Allochromatium vinosum formerly Chromatium vinosum is a mesophilic purple sulfur bacterium belonging to the family Chromatiaceae in the bacterial class Gammaproteobacteria. The genus Allochromatium contains currently five species. All members were isolated from freshwater, brackish water or marine habitats and are predominately obligate phototrophs. Here we describe the features of the organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of a member of the Chromatiaceae within the purple sulfur bacteria thriving in globally occurring habitats. The 3,669,074 bp genome with its 3,302 protein-coding and 64 RNA genes was sequenced within the Joint Genome Institute Community Sequencing Program.
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Affiliation(s)
- Thomas Weissgerber
- Institute for Microbiology & Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - Renate Zigann
- Institute for Microbiology & Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - David Bruce
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | - Yun-juan Chang
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | - John C. Detter
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | - Cliff Han
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | - Loren Hauser
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | | | - Miriam Land
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | | | - Roxanne Tapia
- DOE Joint Genome Institute, Walnut Creek, California, USA
| | - Christiane Dahl
- Institute for Microbiology & Biotechnology, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
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Borisov VB, Gennis RB, Hemp J, Verkhovsky MI. The cytochrome bd respiratory oxygen reductases. BIOCHIMICA ET BIOPHYSICA ACTA 2011; 1807:1398-413. [PMID: 21756872 PMCID: PMC3171616 DOI: 10.1016/j.bbabio.2011.06.016] [Citation(s) in RCA: 374] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 06/23/2011] [Accepted: 06/24/2011] [Indexed: 01/03/2023]
Abstract
Cytochrome bd is a respiratory quinol: O₂ oxidoreductase found in many prokaryotes, including a number of pathogens. The main bioenergetic function of the enzyme is the production of a proton motive force by the vectorial charge transfer of protons. The sequences of cytochromes bd are not homologous to those of the other respiratory oxygen reductases, i.e., the heme-copper oxygen reductases or alternative oxidases (AOX). Generally, cytochromes bd are noteworthy for their high affinity for O₂ and resistance to inhibition by cyanide. In E. coli, for example, cytochrome bd (specifically, cytochrome bd-I) is expressed under O₂-limited conditions. Among the members of the bd-family are the so-called cyanide-insensitive quinol oxidases (CIO) which often have a low content of the eponymous heme d but, instead, have heme b in place of heme d in at least a majority of the enzyme population. However, at this point, no sequence motif has been identified to distinguish cytochrome bd (with a stoichiometric complement of heme d) from an enzyme designated as CIO. Members of the bd-family can be subdivided into those which contain either a long or a short hydrophilic connection between transmembrane helices 6 and 7 in subunit I, designated as the Q-loop. However, it is not clear whether there is a functional consequence of this difference. This review summarizes current knowledge on the physiological functions, genetics, structural and catalytic properties of cytochromes bd. Included in this review are descriptions of the intermediates of the catalytic cycle, the proposed site for the reduction of O₂, evidence for a proton channel connecting this active site to the bacterial cytoplasm, and the molecular mechanism by which a membrane potential is generated.
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Affiliation(s)
- Vitaliy B Borisov
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Leninskie Gory, Moscow 119991, Russian Federation.
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