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Carvalho VCF, Gan AZM, Shon A, Kolakovic S, Freitas EB, Reis MAM, Fradinho JC, Oehmen A. The phototrophic metabolic behaviour of Candidatus accumulibacter. WATER RESEARCH 2024; 259:121865. [PMID: 38851111 DOI: 10.1016/j.watres.2024.121865] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 05/30/2024] [Accepted: 05/31/2024] [Indexed: 06/10/2024]
Abstract
The phototrophic capability of Candidatus Accumulibacter (Accumulibacter), a common polyphosphate accumulating organism (PAO) in enhanced biological phosphorus removal (EBPR) systems, was investigated in this study. Accumulibacter is phylogenetically related to the purple bacteria Rhodocyclus from the family Rhodocyclaceae, which belongs to the class Betaproteobacteria. Rhodocyclus typically exhibits both chemoheterotrophic and phototrophic growth, however, limited studies have evaluated the phototrophic potential of Accumulibacter. To address this gap, short and extended light cycle tests were conducted using a highly enriched Accumulibacter culture (95%) to evaluate its responses to illumination. Results showed that, after an initial period of adaptation to light conditions (approximately 4-5 h), Accumulibacter exhibited complete phosphorus (P) uptake by utilising polyhydroxyalkanoates (PHA), and additionally by consuming glycogen, which contrasted with its typical aerobic metabolism. Mass, energy, and redox balance analyses demonstrated that Accumulibacter needed to employ phototrophic metabolism to meet its energy requirements. Calculations revealed that the light reactions contributed to the generation of, at least more than 67% of the ATP necessary for P uptake and growth. Extended light tests, spanning 21 days with dark/light cycles, suggested that Accumulibacter generated ATP through light during initial operation, however, it likely reverted to conventional anaerobic/aerobic metabolism under dark/light conditions due to microalgal growth in the mixed culture, contributing to oxygen production. In contrast, extended light tests with an enriched Tetrasphaera culture, lacking phototrophic genes in its genome, clearly demonstrated that phototrophic P uptake did not occur. These findings highlight the adaptive metabolic capabilities of Accumulibacter, enabling it to utilise phototrophic pathways for energy generation during oxygen deprivation, which holds the potential to advance phototrophic-EBPR technology development.
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Affiliation(s)
- V C F Carvalho
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - A Z M Gan
- School of Chemical Engineering, University of Queensland, Brisbane, QLD, 4072, Australia
| | - A Shon
- School of Chemical Engineering, University of Queensland, Brisbane, QLD, 4072, Australia
| | - S Kolakovic
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - E B Freitas
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - M A M Reis
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - J C Fradinho
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
| | - A Oehmen
- Associate Laboratory i4HB - Institute for Health and Bioeconomy, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Department of Chemistry, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal; School of Chemical Engineering, University of Queensland, Brisbane, QLD, 4072, Australia.
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Godoy MS, Verdú I, de Miguel SR, Jiménez JD, Prieto MA. Exploring Rhodospirillum rubrum response to high doses of carbon monoxide under light and dark conditions. Appl Microbiol Biotechnol 2024; 108:258. [PMID: 38466440 DOI: 10.1007/s00253-024-13079-5] [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: 11/28/2023] [Revised: 01/14/2024] [Accepted: 02/16/2024] [Indexed: 03/13/2024]
Abstract
Environmental concerns about residues and the traditional disposal methods are driving the search for more environmentally conscious processes, such as pyrolysis and gasification. Their main final product is synthesis gas (syngas) composed of CO, CO2, H2, and methane. Syngas can be converted into various products using CO-tolerant microorganisms. Among them, Rhodospirillum rubrum is highlighted for its biotechnological potential. However, the extent to which high doses of CO affect its physiology is still opaque. For this reason, we have studied R. rubrum behavior under high levels of this gas (up to 2.5 bar), revealing a profound dependence on the presence or absence of light. In darkness, the key variable affected was the lag phase, where the highest levels of CO retarded growth to more than 20 days. Under light, R. rubrum ability to convert CO into CO2 and H2 depended on the presence of an additional carbon source, such as acetate. In those conditions where CO was completely exhausted, CO2 fixation was unblocked, leading to a diauxic growth. To enhance R. rubrum tolerance to CO in darkness, a UV-accelerated adaptive laboratory evolution (UVa-ALE) trial was conducted to isolate clones with shorter lag phases, resulting in the isolation of clones 1.4-2B and 1.7-2A. The adaptation of 1.4-2B was mainly based on mutated enzymes with a metabolic function, while 1.7-3A was mostly affected at regulatory genes, including the anti-repressor PpaA/AerR. Despite these mutations having slight effects on biomass and pigment levels, they successfully provoked a significant reduction in the lag phase (-50%). KEYPOINTS: • CO affects principally R. rubrum lag phase (darkness) and growth rate (light) • CO is converted to CO2/H2 during acetate uptake and inhibits CO2 fixation (light) • UVa-ALE clones showed a 50% reduction in the lag phase (darkness).
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Affiliation(s)
- Manuel S Godoy
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain.
- Interdisciplinary Platform for Sustainable Plastics Towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain.
| | - Irene Verdú
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Present address: Drexel University, Philadelphia, Pennsylvania, USA
| | - Santiago R de Miguel
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics Towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain
| | - José D Jiménez
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics Towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain
| | - M Auxiliadora Prieto
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain.
- Interdisciplinary Platform for Sustainable Plastics Towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain.
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3
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Godoy MS, de Miguel SR, Prieto MA. A singular PpaA/AerR-like protein in Rhodospirillum rubrum rules beyond the boundaries of photosynthesis in response to the intracellular redox state. mSystems 2023; 8:e0070223. [PMID: 38054698 PMCID: PMC10734443 DOI: 10.1128/msystems.00702-23] [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: 07/12/2023] [Accepted: 10/18/2023] [Indexed: 12/07/2023] Open
Abstract
IMPORTANCE Rhodospirillum rubrum vast metabolic versatility places it as a remarkable model bacterium and an excellent biotechnological chassis. The key component of photosynthesis (PS) studied in this work (HP1) stands out among the other members of PpaA/AerR anti-repressor family since it lacks the motif they all share: the cobalamin B-12 binding motif. Despite being reduced and poorly conserved, HP1 stills controls PS as the other members of the family, allowing a fast response to changes in the redox state of the cell. This work also shows that HP1 absence affects genes from relevant biological processes other than PS, including nitrogen fixation and stress response. From a biotechnological perspective, HP1 could be manipulated in approaches where PS is not necessary, such as hydrogen or polyhydroxyalkanoates production, to save energy.
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Affiliation(s)
- Manuel S. Godoy
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy‐CSIC (SusPlast‐CSIC), Madrid, Spain
| | - Santiago R. de Miguel
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy‐CSIC (SusPlast‐CSIC), Madrid, Spain
| | - M. Auxiliadora Prieto
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy‐CSIC (SusPlast‐CSIC), Madrid, Spain
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Alleman AB, Peters JW. Mechanisms for Generating Low Potential Electrons across the Metabolic Diversity of Nitrogen-Fixing Bacteria. Appl Environ Microbiol 2023; 89:e0037823. [PMID: 37154716 PMCID: PMC10231201 DOI: 10.1128/aem.00378-23] [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] [Indexed: 05/10/2023] Open
Abstract
The availability of fixed nitrogen is a limiting factor in the net primary production of all ecosystems. Diazotrophs overcome this limit through the conversion of atmospheric dinitrogen to ammonia. Diazotrophs are phylogenetically diverse bacteria and archaea that exhibit a wide range of lifestyles and metabolisms, including obligate anaerobes and aerobes that generate energy through heterotrophic or autotrophic metabolisms. Despite the diversity of metabolisms, all diazotrophs use the same enzyme, nitrogenase, to reduce N2. Nitrogenase is an O2-sensitive enzyme that requires a high amount of energy in the form of ATP and low potential electrons carried by ferredoxin (Fd) or flavodoxin (Fld). This review summarizes how the diverse metabolisms of diazotrophs utilize different enzymes to generate low potential reducing equivalents for nitrogenase catalysis. These enzymes include substrate-level Fd oxidoreductases, hydrogenases, photosystem I or other light-driven reaction centers, electron bifurcating Fix complexes, proton motive force-driven Rnf complexes, and Fd:NAD(P)H oxidoreductases. Each of these enzymes is critical for generating low potential electrons while simultaneously integrating the native metabolism to balance nitrogenase's overall energy needs. Understanding the diversity of electron transport systems to nitrogenase in various diazotrophs will be essential to guide future engineering strategies aimed at expanding the contributions of biological nitrogen fixation in agriculture.
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Affiliation(s)
- Alexander B. Alleman
- Institute of Biological Chemistry, Washington State University, Pullman, Washington, USA
| | - John W. Peters
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma, USA
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Godoy MS, de Miguel SR, Prieto MA. Aerobic-anaerobic transition boosts poly(3-hydroxybutyrate-co-3-hydroxyvalerate) synthesis in Rhodospirillum rubrum: the key role of carbon dioxide. Microb Cell Fact 2023; 22:47. [PMID: 36899367 PMCID: PMC9999600 DOI: 10.1186/s12934-023-02045-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 02/16/2023] [Indexed: 03/12/2023] Open
Abstract
BACKGROUND Microbially produced bioplastics are specially promising materials since they can be naturally synthesized and degraded, making its end-of-life management more amenable to the environment. A prominent example of these new materials are polyhydroxyalkanoates. These polyesters serve manly as carbon and energy storage and increase the resistance to stress. Their synthesis can also work as an electron sink for the regeneration of oxidized cofactors. In terms of biotechnological applications, the co-polymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), or PHBV, has interesting biotechnological properties due to its lower stiffness and fragility compared to the homopolymer poly(3-hydroxybutyrate) (P3HB). In this work, we explored the potentiality of Rhodospirillum rubrum as a producer of this co-polymer, exploiting its metabolic versatility when grown in different aeration conditions and photoheterotrophically. RESULTS When shaken flasks experiments were carried out with limited aeration using fructose as carbon source, PHBV production was triggered reaching 29 ± 2% CDW of polymer accumulation with a 75 ± 1%mol of 3-hydroxyvalerate (3HV) (condition C2). Propionate and acetate were secreted in this condition. The synthesis of PHBV was exclusively carried out by the PHA synthase PhaC2. Interestingly, transcription of cbbM coding RuBisCO, the key enzyme of the Calvin-Benson-Bassham cycle, was similar in aerobic and microaerobic/anaerobic cultures. The maximal PHBV yield (81% CDW with 86%mol 3HV) was achieved when cells were transferred from aerobic to anaerobic conditions and controlling the CO2 concentration by adding bicarbonate to the culture. In these conditions, the cells behaved like resting cells, since polymer accumulation prevailed over residual biomass formation. In the absence of bicarbonate, cells could not adapt to an anaerobic environment in the studied lapse. CONCLUSIONS We found that two-phase growth (aerobic-anaerobic) significantly improved the previous report of PHBV production in purple nonsulfur bacteria, maximizing the polymer accumulation at the expense of other components of the biomass. The presence of CO2 is key in this process demonstrating the involvement of the Calvin-Benson-Bassham in the adaptation to changes in oxygen availability. These results stand R. rubrum as a promising producer of high-3HV-content PHBV co-polymer from fructose, a PHBV unrelated carbon source.
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Affiliation(s)
- Manuel S Godoy
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain.
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain.
| | - Santiago R de Miguel
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain
| | - M Auxiliadora Prieto
- Polymer Biotechnology Lab, Biological Research Centre Margarita Salas, Spanish National Research Council (CIB-CSIC), Madrid, Spain.
- Interdisciplinary Platform for Sustainable Plastics towards a Circular Economy-CSIC (SusPlast-CSIC), Madrid, Spain.
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Capson-Tojo G, Batstone DJ, Hülsen T. Expanding mechanistic models to represent purple phototrophic bacteria enriched cultures growing outdoors. WATER RESEARCH 2023; 229:119401. [PMID: 36450178 DOI: 10.1016/j.watres.2022.119401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 10/17/2022] [Accepted: 11/20/2022] [Indexed: 06/17/2023]
Abstract
The economic feasibility of purple phototrophic bacteria (PPB) for resource recovery relies on using enriched-mixed cultures and sunlight. This work presents an extended Photo-Anaerobic Model (ePAnM), considering: (i) the diverse metabolic capabilities of PPB, (ii) microbial clades interacting with PPB, and (iii) varying environmental conditions. Key kinetic and stoichiometric parameters were either determined experimentally (with dedicated tests), calculated, or gathered from literature. The model was calibrated and validated using different datasets from an outdoors demonstration-scale reactor, as well as results from aerobic and anaerobic batch tests. The ePAnM was able to predict the concentrations of key compounds/components (e.g., COD, volatile fatty acids, and nutrients), as well as microbial communities (with anaerobic systems dominated by fermenters and PPB). The results underlined the importance of considering other microbial clades and varying environmental conditions. The model predicted a minimum hydraulic retention time of 0.5 d-1. A maximum width of 10 cm in flat plate reactors should not be exceeded. Simulations showed the potential of a combined day-anaerobic/night-aerobic operational strategy to allow efficient continuous operation.
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Affiliation(s)
- Gabriel Capson-Tojo
- Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD 4072, Australia; Department of Chemical Engineering, CRETUS, Universidade de Santiago de Compostela, Santiago de Compostela, Galicia 15782, Spain; INRAE, University Montpellier, LBE, 102 Avenue des Etangs, Narbonne 11100, France.
| | - Damien J Batstone
- Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Tim Hülsen
- Australian Centre for Water and Environmental Biotechnology, The University of Queensland, Brisbane, QLD 4072, Australia
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Alloul A, Blansaer N, Cabecas Segura P, Wattiez R, Vlaeminck SE, Leroy B. Dehazing redox homeostasis to foster purple bacteria biotechnology. Trends Biotechnol 2023; 41:106-119. [PMID: 35843758 DOI: 10.1016/j.tibtech.2022.06.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 06/14/2022] [Accepted: 06/17/2022] [Indexed: 12/27/2022]
Abstract
Purple non-sulfur bacteria (PNSB) show great potential for environmental and industrial biotechnology, producing microbial protein, biohydrogen, polyhydroxyalkanoates (PHAs), pigments, etc. When grown photoheterotrophically, the carbon source is typically more reduced than the PNSB biomass, which leads to a redox imbalance. To mitigate the excess of electrons, PNSB can exhibit several 'electron sinking' strategies, such as CO2 fixation, N2 fixation, and H2 and PHA production. The lack of a comprehensive (over)view of these redox strategies is hindering the implementation of PNSB for biotechnology applications. This review aims to present the state of the art of redox homeostasis in phototrophically grown PNSB, presenting known and theoretically expected strategies, and discussing them from stoichiometric, thermodynamic, metabolic, and economic points of view.
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Affiliation(s)
- Abbas Alloul
- Research Group of Sustainable Energy, Air and Water Technology, Department of Bioscience Engineering, University of Antwerp, Antwerpen, Belgium.
| | - Naïm Blansaer
- Research Group of Sustainable Energy, Air and Water Technology, Department of Bioscience Engineering, University of Antwerp, Antwerpen, Belgium
| | | | - Ruddy Wattiez
- Laboratory of Proteomics and Microbiology, University of Mons, Mons, Belgium
| | - Siegfried E Vlaeminck
- Research Group of Sustainable Energy, Air and Water Technology, Department of Bioscience Engineering, University of Antwerp, Antwerpen, Belgium
| | - Baptiste Leroy
- Laboratory of Proteomics and Microbiology, University of Mons, Mons, Belgium
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Syed Z, Sogani M, Sharma G, Sonu K, Rajvanshi J, Gupta NS. Framework to improve biohydrogen generation with estrogen co-metabolism under complete suppression of nitrogen source. BIORESOURCE TECHNOLOGY 2022; 360:127595. [PMID: 35803446 DOI: 10.1016/j.biortech.2022.127595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Revised: 07/01/2022] [Accepted: 07/03/2022] [Indexed: 06/15/2023]
Abstract
The current work provides insights for improving the hydrogen output while degrading emerging contaminants using Rhodopseudomonas palustris. The changes in the growth rate of a microorganism due to different substrate inputs affects the hydrogen production due to metabolic route changes. The different ratios of glutamate and glycerol as nitrogen and carbon sources along with the presence of ethinylestradiol (EE2) in the photofermenter affected the flux of electrons being directed towards biosynthesis and biohydrogen generation. The combination of glutamate and glycerol in different ratios (Glu:Gly; 0, 0.20 and 0.54) along with estrogen showed no significant difference in the bacteriochlorophyll concentrations. The highest biomass concentration (0.013 h-1) was in ratio of 0.54 while maximum specific hydrogen production (1.9 ± 0.05 ml g-1 biomass h-1) was observed under complete suppression of nitrogen (0; without Glu; non-growing condition) with resultant improved estrogen degradation of about 78% in 168 h by R. palustris strain MDOC01.
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Affiliation(s)
- Zainab Syed
- Department of Biosciences, Manipal University Jaipur, Jaipur 303007, Rajasthan, India
| | - Monika Sogani
- Department of Biosciences, Manipal University Jaipur, Jaipur 303007, Rajasthan, India.
| | - Gopesh Sharma
- Department of Biosciences, Manipal University Jaipur, Jaipur 303007, Rajasthan, India
| | - Kumar Sonu
- Department of Mechanical Engineering, Kashi Institute of Technology, Varanasi 221307, Uttar Pradesh, India
| | - Jayana Rajvanshi
- Department of Biosciences, Manipal University Jaipur, Jaipur 303007, Rajasthan, India
| | - Nishan Sen Gupta
- Department of Biosciences, Manipal University Jaipur, Jaipur 303007, Rajasthan, India
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Chowdhury NB, Alsiyabi A, Saha R. Characterizing the Interplay of Rubisco and Nitrogenase Enzymes in Anaerobic-Photoheterotrophically Grown Rhodopseudomonas palustris CGA009 through a Genome-Scale Metabolic and Expression Model. Microbiol Spectr 2022; 10:e0146322. [PMID: 35730964 PMCID: PMC9431616 DOI: 10.1128/spectrum.01463-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 05/31/2022] [Indexed: 11/20/2022] Open
Abstract
Rhodopseudomonas palustris CGA009 is a Gram-negative purple nonsulfur bacterium that grows phototrophically by fixing carbon dioxide and nitrogen or chemotrophically by fixing or catabolizing a wide array of substrates, including lignin breakdown products for its carbon and fixing nitrogen for its nitrogen requirements. It can grow aerobically or anaerobically and can use light, inorganic, and organic compounds for energy production. Due to its ability to convert different carbon sources into useful products during anaerobic growth, this study reconstructed a metabolic and expression (ME) model of R. palustris to investigate its anaerobic-photoheterotrophic growth. Unlike metabolic (M) models, ME models include transcription and translation reactions along with macromolecules synthesis and couple these reactions with growth rate. This unique feature of the ME model led to nonlinear growth curve predictions, which matched closely with experimental growth rate data. At the theoretical maximum growth rate, the ME model suggested a diminishing rate of carbon fixation and predicted malate dehydrogenase and glycerol-3 phosphate dehydrogenase as alternate electron sinks. Moreover, the ME model also identified ferredoxin as a key regulator in distributing electrons between major redox balancing pathways. Because ME models include the turnover rate for each metabolic reaction, it was used to successfully capture experimentally observed temperature regulation of different nitrogenases. Overall, these unique features of the ME model demonstrated the influence of nitrogenases and rubiscos on R. palustris growth and predicted a key regulator in distributing electrons between major redox balancing pathways, thus establishing a platform for in silico investigation of R. palustris metabolism from a multiomics perspective. IMPORTANCE In this work, we reconstructed the first ME model for a purple nonsulfur bacterium (PNSB). Using the ME model, different aspects of R. palustris metabolism were examined. First, the ME model was used to analyze how reducing power entering the R. palustris cell through organic carbon sources gets partitioned into biomass, carbon dioxide fixation, and nitrogen fixation. Furthermore, the ME model predicted electron flux through ferredoxin as a major bottleneck in distributing electrons to nitrogenase enzymes. Next, the ME model characterized different nitrogenase enzymes and successfully recapitulated experimentally observed temperature regulations of those enzymes. Identifying the bottleneck responsible for transferring an electron to nitrogenase enzymes and recapitulating the temperature regulation of different nitrogenase enzymes can have profound implications in metabolic engineering, such as hydrogen production from R. palustris. Another interesting application of this ME model can be to take advantage of its redox balancing strategy to gain an understanding of the regulatory mechanism of biodegradable plastic production precursors, such as polyhydroxybutyrate (PHB).
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Affiliation(s)
- Niaz Bahar Chowdhury
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Adil Alsiyabi
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
| | - Rajib Saha
- Chemical and Biomolecular Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, USA
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Bayon-Vicente G, Marchand E, Ducrotois J, Dufrasne FE, Hallez R, Wattiez R, Leroy B. Analysis of the Involvement of the Isoleucine Biosynthesis Pathway in Photoheterotrophic Metabolism of Rhodospirillum rubrum. Front Microbiol 2021; 12:731976. [PMID: 34621257 PMCID: PMC8490811 DOI: 10.3389/fmicb.2021.731976] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Accepted: 08/26/2021] [Indexed: 12/05/2022] Open
Abstract
Purple non-sulfur bacteria (PNSB) are recognized as a highly versatile group of bacteria that assimilate a broad range of carbon sources. Growing heterotrophically, PNSB such as Rhodospirillum rubrum (Rs. rubrum) generate reduced equivalents that are used for biomass production. However, under photoheterotrophic conditions, more reduced electron carriers than required to produce biomass are generated. The excess of reduced equivalents still needs to be oxidized for the metabolism to optimally operate. These metabolic reactions are known as electron sinks. Most PNSB rely on the CO2-fixing Calvin cycle and H2 production to oxidize these reduced equivalents. In addition to these well-described electron sinks, the involvement of some pathways, such as polyhydroxyalkanoate (PHA) biosynthesis, in redox poise is still controversial and requires further studies. Among them, isoleucine biosynthesis has been recently highlighted as one of these potential pathways. Here, we explore the role of isoleucine biosynthesis in Rs. rubrum. Our results demonstrate that the isoleucine content is higher under illuminated conditions and that submitting Rs. rubrum to light stress further increases this phenomenon. Moreover, we explore the production of (p)ppGpp in Rs. rubrum and its potential link with light stress. We further demonstrate that a fully functional isoleucine biosynthesis pathway could be an important feature for the onset of Rs. rubrum growth under photoheterotrophic conditions even in the presence of an exogenous isoleucine source. Altogether, our data suggest that isoleucine biosynthesis could play a key role in redox homeostasis.
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Affiliation(s)
- Guillaume Bayon-Vicente
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Elie Marchand
- Bacterial Cell Cycle & Development (BCcD), Biology of Microorganisms Research Unit (URBM), Namur Research Institute for Life Science (NARILIS), University of Namur, Namur, Belgium
| | - Jeson Ducrotois
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - François E. Dufrasne
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Regis Hallez
- Bacterial Cell Cycle & Development (BCcD), Biology of Microorganisms Research Unit (URBM), Namur Research Institute for Life Science (NARILIS), University of Namur, Namur, Belgium
- Namur Research College (NARC), University of Namur, Namur, Belgium
- WELBIO, University of Namur, Namur, Belgium
| | - Ruddy Wattiez
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
| | - Baptiste Leroy
- Laboratory of Proteomics and Microbiology, Research Institute for Biosciences, University of Mons, Mons, Belgium
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Doloman A, Seefeldt LC. An Experimentally Evaluated Thermodynamic Approach to Estimate Growth of Photoheterotrophic Purple Non-sulfur Bacteria. Front Microbiol 2020; 11:540378. [PMID: 33013778 PMCID: PMC7494753 DOI: 10.3389/fmicb.2020.540378] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 08/17/2020] [Indexed: 11/21/2022] Open
Abstract
Distribution of energy during the growth and formation of useful chemicals by microorganisms can define the overall performance of a biotechnological system. However, to date, this distribution has not been used to reliably predict growth characteristics of phototrophic microorganisms. The presented research addresses this application by estimating the photon-associated Gibbs energy delivered for the photoheterotrophic growth of purple non-sulfur bacteria and production of dihydrogen. The approach is successfully evaluated with the data from a fed-batch growth of Rhodopseudomonas palustris nifA∗ fixing N2 gas in phototrophic conditions and a reliable prediction of growth characteristics is demonstrated. Additionally, literature-available experimental data is collected and used for evaluation of the presented thermodynamic approach to predict photoheterotrophic growth yields. A proposed thermodynamic framework with modification to account for the phototrophic growth can be used to predict growth rates in broader environmental niches and to assess the possibility for the development of novel biotechnological applications in light-induced biological systems.
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Affiliation(s)
- Anna Doloman
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT, United States
| | - Lance C Seefeldt
- Department of Chemistry and Biochemistry, Utah State University, Logan, UT, United States
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12
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Wang H, Waluk D, Dixon R, Nordlund S, Norén A. Energy shifts induce membrane sequestration of DraG in Rhodospirillum rubrum independent of the ammonium transporters and diazotrophic conditions. FEMS Microbiol Lett 2019; 365:5053809. [PMID: 30010831 PMCID: PMC6067124 DOI: 10.1093/femsle/fny176] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 07/10/2018] [Indexed: 01/15/2023] Open
Abstract
Metabolic regulation of Rhodospirillum rubrum nitrogenase is mediated at the post-translational level by the enzymes DraT and DraG when subjected to changes in nitrogen or energy status. DraT is activated during switch-off, while DraG is inactivated by reversible membrane association. We confirm here that the ammonium transporter, AmtB1, rather than its paralog AmtB2, is required for ammonium induced switch-off. Amongst several substitutions at the N100 position in DraG, only N100K failed to locate to the membrane following ammonium shock, suggesting loss of interaction through charge repulsion. When switch-off was induced by lowering energy levels, either by darkness during photosynthetic growth or oxygen depletion under respiratory conditions, reversible membrane sequestration of DraG was independent of AmtB proteins and occurred even under non-diazotrophic conditions. We propose that under these conditions, changes in redox status or possibly membrane potential induce interactions between DraG and another membrane protein in response to the energy status.
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Affiliation(s)
- Helen Wang
- Department of Medical Biochemistry and Microbiology, Uppsala Biomedicinska Centrum, Husarg.3, S-75237 Uppsala, Sweden
| | - Dominik Waluk
- Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Svante Arrhenius v. 16C, Stockholm S-10691, Sweden
| | - Ray Dixon
- Department of Molecular Microbiology, John Innes Centre, Norwich NR47 UH, UK
| | - Stefan Nordlund
- Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Svante Arrhenius v. 16C, Stockholm S-10691, Sweden
| | - Agneta Norén
- Department of Biochemistry and Biophysics, Arrhenius Laboratories, Stockholm University, Svante Arrhenius v. 16C, Stockholm S-10691, Sweden
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13
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Modeling the Interplay between Photosynthesis, CO 2 Fixation, and the Quinone Pool in a Purple Non-Sulfur Bacterium. Sci Rep 2019; 9:12638. [PMID: 31477760 PMCID: PMC6718658 DOI: 10.1038/s41598-019-49079-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2019] [Accepted: 08/19/2019] [Indexed: 11/17/2022] Open
Abstract
Rhodopseudomonas palustris CGA009 is a purple non-sulfur bacterium that can fix carbon dioxide (CO2) and nitrogen or break down organic compounds for its carbon and nitrogen requirements. Light, inorganic, and organic compounds can all be used for its source of energy. Excess electrons produced during its metabolic processes can be exploited to produce hydrogen gas or biodegradable polyesters. A genome-scale metabolic model of the bacterium was reconstructed to study the interactions between photosynthesis, CO2 fixation, and the redox state of the quinone pool. A comparison of model-predicted flux values with available Metabolic Flux Analysis (MFA) fluxes yielded predicted errors of 5–19% across four different growth substrates. The model predicted the presence of an unidentified sink responsible for the oxidation of excess quinols generated by the TCA cycle. Furthermore, light-dependent energy production was found to be highly dependent on the quinol oxidation rate. Finally, the extent of CO2 fixation was predicted to be dependent on the amount of ATP generated through the electron transport chain, with excess ATP going toward the energy-demanding Calvin-Benson-Bassham (CBB) pathway. Based on this analysis, it is hypothesized that the quinone redox state acts as a feed-forward controller of the CBB pathway, signaling the amount of ATP available.
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14
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Chen Q, Arents J, Schuurmans JM, Ganapathy S, de Grip WJ, Cheregi O, Funk C, dos Santos FB, Hellingwerf KJ. Combining retinal-based and chlorophyll-based (oxygenic) photosynthesis: Proteorhodopsin expression increases growth rate and fitness of a ∆PSI strain of Synechocystis sp. PCC6803. Metab Eng 2019; 52:68-76. [DOI: 10.1016/j.ymben.2018.11.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2018] [Revised: 11/09/2018] [Accepted: 11/10/2018] [Indexed: 11/28/2022]
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15
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Abstract
The utilization of light energy to power organic-chemical transformations is a fundamental strategy of the terrestrial energy cycle. Inspired by the elegance of natural photosynthesis, much interdisciplinary research effort has been devoted to the construction of simplified cell mimics based on artificial vesicles to provide a novel tool for biocatalytic cascade reactions with energy-demanding steps. By inserting natural or even artificial photosynthetic systems into liposomes or polymersomes, the light-driven proton translocation and the resulting formation of electrochemical gradients have become possible. This is the basis for the conversion of photonic into chemical energy in form of energy-rich molecules such as adenosine triphosphate (ATP), which can be further utilized by energy-dependent biocatalytic reactions, e.g. carbon fixation. This review compares liposomes and polymersomes as artificial compartments and summarizes the types of light-driven proton pumps that have been employed in artificial photosynthesis so far. We give an overview over the methods affecting the orientation of the photosystems within the membranes to ensure a unidirectional transport of molecules and highlight recent examples of light-driven biocatalysis in artificial vesicles. Finally, we summarize the current achievements and discuss the next steps needed for the transition of this technology from the proof-of-concept status to preparative applications.
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16
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Kirchhoff C, Ebert M, Jahn D, Cypionka H. Chemiosmotic Energy Conservation in Dinoroseobacter shibae: Proton Translocation Driven by Aerobic Respiration, Denitrification, and Photosynthetic Light Reaction. Front Microbiol 2018; 9:903. [PMID: 29867814 PMCID: PMC5954134 DOI: 10.3389/fmicb.2018.00903] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Accepted: 04/18/2018] [Indexed: 11/13/2022] Open
Abstract
Dinoroseobacter shibae is an aerobic anoxygenic phototroph and able to utilize light energy to support its aerobic energy metabolism. Since the cells can also grow anaerobically with nitrate and nitrite as terminal electron acceptor, we were interested in how the cells profit from photosynthesis during denitrification and what the steps of chemiosmotic energy conservation are. Therefore, we conducted proton translocation experiments and compared O2-, NO3-, and NO2- respiration during different light regimes and in the dark. We used wild type cells and transposon mutants with knocked-out nitrate- and nitrite- reductase genes (napA and nirS), as well as a mutant (ppsR) impaired in bacteriochlorophyll a synthesis. Light had a positive impact on proton translocation, independent of the type of terminal electron acceptor present. In the absence of an electron acceptor, however, light did not stimulate proton translocation. The light-driven add-on to proton translocation was about 1.4 H+/e- for O2 respiration and about 1.1 H+/e- for NO3- and NO2-. We could see that the chemiosmotic energy conservation during aerobic respiration involved proton translocation, mediated by the NADH dehydrogenase, the cytochrome bc1 complex, and the cytochrome c oxidase. During denitrification the last proton translocation step of the electron transport was missing, resulting in a lower H+/e- ratio during anoxia. Furthermore, we studied the type of light-harvesting and found that the cells were able to channel light from the green–blue spectrum most efficiently, while red light has only minor impact. This fits well with the depth profiles for D. shibae abundance in the ocean and the penetration depth of light with different wavelengths into the water column.
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Affiliation(s)
- Christian Kirchhoff
- Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Matthias Ebert
- Institute of Microbiology, Braunschweig University of Technology, Braunschweig, Germany
| | - Dieter Jahn
- Institute of Microbiology, Braunschweig University of Technology, Braunschweig, Germany
| | - Heribert Cypionka
- Institute for Chemistry and Biology of the Marine Environment, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
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17
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Nev OA, Van Den Berg HA. Mathematical models of microbial growth and metabolism: a whole-organism perspective. Sci Prog 2017; 100:343-362. [PMID: 29113620 PMCID: PMC10365175 DOI: 10.3184/003685017x15063357842583] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We review the principles underpinning the development of mathematical models of the metabolic activities of micro-organisms. Such models are important to understand and chart the substantial contributions made by micro-organisms to geochemical cycles, and also to optimise the performance of bioreactors that exploit the biochemical capabilities of these organisms. We advocate an approach based on the principle of dynamic allocation. We survey the biological background that motivates this approach, including nutrient assimilation, the regulation of gene expression, and the principles of microbial growth. In addition, we discuss the classic models of microbial growth as well as contemporary approaches. The dynamic allocation theory generalises these classic models in a natural manner and is readily amenable to the additional information provided by transcriptomics and proteomics approaches. Finally, we touch upon these organising principles in the context of the transition from the free-living unicellular mode of life to multicellularity.
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18
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Graham PJ, Nguyen B, Burdyny T, Sinton D. A penalty on photosynthetic growth in fluctuating light. Sci Rep 2017; 7:12513. [PMID: 28970553 PMCID: PMC5624943 DOI: 10.1038/s41598-017-12923-1] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 09/20/2017] [Indexed: 12/21/2022] Open
Abstract
Fluctuating light is the norm for photosynthetic organisms, with a wide range of frequencies (0.00001 to 10 Hz) owing to diurnal cycles, cloud cover, canopy shifting and mixing; with broad implications for climate change, agriculture and bioproduct production. Photosynthetic growth in fluctuating light is generally considered to improve with increasing fluctuation frequency. Here we demonstrate that the regulation of photosynthesis imposes a penalty on growth in fluctuating light for frequencies in the range of 0.01 to 0.1 Hz (organisms studied: Synechococcus elongatus and Chlamydomonas reinhardtii). We provide a comprehensive sweep of frequencies and duty cycles. In addition, we develop a 2nd order model that identifies the source of the penalty to be the regulation of the Calvin cycle – present at all frequencies but compensated at high frequencies by slow kinetics of RuBisCO.
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Affiliation(s)
- Percival J Graham
- University of Toronto Mechanical and Industrial Engineering, Toronto, Canada
| | - Brian Nguyen
- University of Toronto Mechanical and Industrial Engineering, Toronto, Canada
| | - Thomas Burdyny
- University of Toronto Mechanical and Industrial Engineering, Toronto, Canada
| | - David Sinton
- University of Toronto Mechanical and Industrial Engineering, Toronto, Canada.
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19
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Sandri F, Fedi S, Cappelletti M, Calabrese FM, Turner RJ, Zannoni D. Biphenyl Modulates the Expression and Function of Respiratory Oxidases in the Polychlorinated-Biphenyls Degrader Pseudomonas pseudoalcaligenes KF707. Front Microbiol 2017; 8:1223. [PMID: 28713350 PMCID: PMC5492768 DOI: 10.3389/fmicb.2017.01223] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/16/2017] [Indexed: 11/13/2022] Open
Abstract
Pseudomonas pseudoalcaligenes KF707 is a soil bacterium which is known for its capacity to aerobically degrade harmful organic compounds such as polychlorinated biphenyls (PCBs) using biphenyl as co-metabolite. Here we provide the first genetic and functional analysis of the KF707 respiratory terminal oxidases in cells grown with two different carbon sources: glucose and biphenyl. We identified five terminal oxidases in KF707: two c(c)aa3 type oxidases (Caa3 and Ccaa3), two cbb3 type oxidases (Cbb31 and Cbb32), and one bd type cyanide-insensitive quinol oxidase (CIO). While the activity and expression of both Cbb31 and Cbb32 oxidases was prevalent in glucose grown cells as compared to the other oxidases, the activity and expression of the Caa3 oxidase increased considerably only when biphenyl was used as carbon source in contrast to the Cbb32 oxidase which was repressed. Further, the respiratory activity and expression of CIO was up-regulated in a Cbb31 deletion strain as compared to W.T. whereas the CIO up-regulation was not present in Cbb32 and C(c)aa3 deletion mutants. These results, together, reveal that both function and expression of cbb3 and caa3 type oxidases in KF707 are modulated by biphenyl which is the co-metabolite needed for the activation of the PCBs-degradation pathway.
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Affiliation(s)
- Federica Sandri
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Stefano Fedi
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Martina Cappelletti
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
| | - Francesco M Calabrese
- Department of Biosciences, Biotechnology and Pharmacological Sciences, University of Bari "Aldo Moro"Bari, Italy.,Department of Biology, University of Bari "Aldo Moro"Bari, Italy
| | - Raymond J Turner
- Department of Biological Sciences, University of CalgaryCalgary, AB, Canada
| | - Davide Zannoni
- Department of Pharmacy and Biotechnology, University of BolognaBologna, Italy
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20
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Hitchcock A, Hunter CN, Sener M. Determination of Cell Doubling Times from the Return-on-Investment Time of Photosynthetic Vesicles Based on Atomic Detail Structural Models. J Phys Chem B 2017; 121:3787-3797. [PMID: 28301162 DOI: 10.1021/acs.jpcb.6b12335] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cell doubling times of the purple bacterium Rhodobacter sphaeroides during photosynthetic growth are determined experimentally and computationally as a function of illumination. For this purpose, energy conversion processes in an intracytoplasmic membrane vesicle, the chromatophore, are described based on an atomic detail structural model. The cell doubling time and its illumination dependence are computed in terms of the return-on-investment (ROI) time of the chromatophore, determined computationally from the ATP production rate, and the mass ratio of chromatophores in the cell, determined experimentally from whole cell absorbance spectra. The ROI time is defined as the time it takes to produce enough ATP to pay for the construction of another chromatophore. The ROI time of the low light-growth chromatophore is 4.5-2.6 h for a typical illumination range of 10-100 μmol photons m-2 s-1, respectively, with corresponding cell doubling times of 8.2-3.9 h. When energy expenditure is considered as a currency, the benefit-to-cost ratio computed for the chromatophore as an energy harvesting device is 2-8 times greater than for photovoltaic and fossil fuel-based energy solutions and the corresponding ROI times are approximately 3-4 orders of magnitude shorter for the chromatophore than for synthetic systems.
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Affiliation(s)
- Andrew Hitchcock
- Department of Molecular Biology and Biotechnology, University of Sheffield , Sheffield S10 2TN, U.K
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield , Sheffield S10 2TN, U.K
| | - Melih Sener
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.,Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States
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21
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Sener M, Strumpfer J, Singharoy A, Hunter CN, Schulten K. Overall energy conversion efficiency of a photosynthetic vesicle. eLife 2016; 5. [PMID: 27564854 PMCID: PMC5001839 DOI: 10.7554/elife.09541] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Accepted: 07/11/2016] [Indexed: 11/25/2022] Open
Abstract
The chromatophore of purple bacteria is an intracellular spherical vesicle that exists in numerous copies in the cell and that efficiently converts sunlight into ATP synthesis, operating typically under low light conditions. Building on an atomic-level structural model of a low-light-adapted chromatophore vesicle from Rhodobacter sphaeroides, we investigate the cooperation between more than a hundred protein complexes in the vesicle. The steady-state ATP production rate as a function of incident light intensity is determined after identifying quinol turnover at the cytochrome bc1 complex (cytbc1) as rate limiting and assuming that the quinone/quinol pool of about 900 molecules acts in a quasi-stationary state. For an illumination condition equivalent to 1% of full sunlight, the vesicle exhibits an ATP production rate of 82 ATP molecules/s. The energy conversion efficiency of ATP synthesis at illuminations corresponding to 1%–5% of full sunlight is calculated to be 0.12–0.04, respectively. The vesicle stoichiometry, evolutionarily adapted to the low light intensities in the habitat of purple bacteria, is suboptimal for steady-state ATP turnover for the benefit of protection against over-illumination. DOI:http://dx.doi.org/10.7554/eLife.09541.001 Photosynthesis, or the conversion of light energy into chemical energy, is a process that powers almost all life on Earth. Plants and certain bacteria share similar processes to perform photosynthesis, though the purple bacterium Rhodobacter sphaeroides uses a photosynthetic system that is much less complex than that in plants. Light harvesting inside the bacterium takes place in up to hundreds of compartments called chromatophores. Each chromatophore in turn contains hundreds of cooperating proteins that together absorb the energy of sunlight and convert and store it in molecules of ATP, the universal energy currency of all cells. The chromatophore of primitive purple bacteria provides a model for more complex photosynthetic systems in plants. Though researchers had characterized its individual components over the years, less was known about the overall architecture of the chromatophore and how its many components work together to harvest light energy efficiently and robustly. This knowledge would provide insight into the evolutionary pressures that shaped the chromatophore and its ability to work efficiently at different light intensities. Sener et al. now present a highly detailed structural model of the chromatophore of purple bacteria based on the findings of earlier studies. The model features the position of every atom of the constituent proteins and is used to examine how energy is transferred and converted. Sener et al. describe the sequence of energy conversion steps and calculate the overall energy conversion efficiency, namely how much of the light energy arriving at the microorganism is stored as ATP. These calculations show that the chromatophore is optimized to produce chemical energy at low light levels typical of purple bacterial habitats, and dissipate excess energy to avoid being damaged under brighter light. The chromatophore’s architecture also displays robustness against perturbations of its components. In the future, the approach used by Sener et al. to describe light harvesting in this bacterial compartment can be applied to more complex systems, such as those in plants. DOI:http://dx.doi.org/10.7554/eLife.09541.002
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Affiliation(s)
- Melih Sener
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States.,Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Johan Strumpfer
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States
| | - Abhishek Singharoy
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States
| | - C Neil Hunter
- Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, United Kingdom
| | - Klaus Schulten
- Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, United States.,Department of Physics, University of Illinois at Urbana-Champaign, Urbana, United States.,Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, United States
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22
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Talaue CO, del Rosario RCH, Pfeiffer F, Mendoza ER, Oesterhelt D. Model Construction and Analysis of Respiration in Halobacterium salinarum. PLoS One 2016; 11:e0151839. [PMID: 27011330 PMCID: PMC4806987 DOI: 10.1371/journal.pone.0151839] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 03/05/2016] [Indexed: 12/05/2022] Open
Abstract
The archaeon Halobacterium salinarum can produce energy using three different processes, namely photosynthesis, oxidative phosphorylation and fermentation of arginine, and is thus a model organism in bioenergetics. Compared to its bacteriorhodopsin-driven photosynthesis, less attention has been devoted to modeling its respiratory pathway. We created a system of ordinary differential equations that models its oxidative phosphorylation. The model consists of the electron transport chain, the ATP synthase, the potassium uniport and the sodium-proton antiport. By fitting the model parameters to experimental data, we show that the model can explain data on proton motive force generation, ATP production, and the charge balancing of ions between the sodium-proton antiporter and the potassium uniport. We performed sensitivity analysis of the model parameters to determine how the model will respond to perturbations in parameter values. The model and the parameters we derived provide a resource that can be used for analytical studies of the bioenergetics of H. salinarum.
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Affiliation(s)
- Cherryl O. Talaue
- Institute of Mathematics, University of the Philippines, Diliman, Quezon City, Philippines
| | - Ricardo C. H. del Rosario
- Institute of Mathematics, University of the Philippines, Diliman, Quezon City, Philippines
- Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Martinsried, Germany
- * E-mail:
| | - Friedhelm Pfeiffer
- Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Martinsried, Germany
| | - Eduardo R. Mendoza
- Institute of Mathematics, University of the Philippines, Diliman, Quezon City, Philippines
- Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Martinsried, Germany
| | - Dieter Oesterhelt
- Max Planck Institute of Biochemistry, Department of Membrane Biochemistry, Martinsried, Germany
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23
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Bettenbrock K, Bai H, Ederer M, Green J, Hellingwerf KJ, Holcombe M, Kunz S, Rolfe MD, Sanguinetti G, Sawodny O, Sharma P, Steinsiek S, Poole RK. Towards a systems level understanding of the oxygen response of Escherichia coli. Adv Microb Physiol 2014; 64:65-114. [PMID: 24797925 DOI: 10.1016/b978-0-12-800143-1.00002-6] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Escherichia coli is a facultatively anaerobic bacterium. With glucose if no external electron acceptors are available, ATP is produced by substrate level phosphorylation. The intracellular redox balance is maintained by mixed-acid fermentation, that is, the production and excretion of several organic acids. When oxygen is available, E. coli switches to aerobic respiration to achieve redox balance and optimal energy conservation by proton translocation linked to electron transfer. The switch between fermentative and aerobic respiratory growth is driven by extensive changes in gene expression and protein synthesis, resulting in global changes in metabolic fluxes and metabolite concentrations. This oxygen response is determined by the interaction of global and local genetic regulatory mechanisms, as well as by enzymatic regulation. The response is affected by basic physical constraints such as diffusion, thermodynamics and the requirement for a balance of carbon, electrons and energy (predominantly the proton motive force and the ATP pool). A comprehensive systems level understanding of the oxygen response of E. coli requires the integrated interpretation of experimental data that are pertinent to the multiple levels of organization that mediate the response. In the pan-European venture, Systems Biology of Microorganisms (SysMO) and specifically within the project Systems Understanding of Microbial Oxygen Metabolism (SUMO), regulator activities, gene expression, metabolite levels and metabolic flux datasets were obtained using a standardized and reproducible chemostat-based experimental system. These different types and qualities of data were integrated using mathematical models. The approach described here has revealed a much more detailed picture of the aerobic-anaerobic response, especially for the environmentally critical microaerobic range that is located between unlimited oxygen availability and anaerobiosis.
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Affiliation(s)
- Katja Bettenbrock
- Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany.
| | - Hao Bai
- Department of Computer Science, The University of Sheffield, Sheffield, United Kingdom
| | - Michael Ederer
- Institute for System Dynamics, University of Stuttgart, Stuttgart, Germany
| | - Jeffrey Green
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Klaas J Hellingwerf
- Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
| | - Michael Holcombe
- Department of Computer Science, The University of Sheffield, Sheffield, United Kingdom
| | - Samantha Kunz
- Institute for System Dynamics, University of Stuttgart, Stuttgart, Germany
| | - Matthew D Rolfe
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Guido Sanguinetti
- School of Informatics, University of Edinburgh, Edinburgh, United Kingdom
| | - Oliver Sawodny
- Institute for System Dynamics, University of Stuttgart, Stuttgart, Germany
| | - Poonam Sharma
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
| | - Sonja Steinsiek
- Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Robert K Poole
- Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield, United Kingdom
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24
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Henkel SG, Beek AT, Steinsiek S, Stagge S, Bettenbrock K, de Mattos MJT, Sauter T, Sawodny O, Ederer M. Basic regulatory principles of Escherichia coli's electron transport chain for varying oxygen conditions. PLoS One 2014; 9:e107640. [PMID: 25268772 PMCID: PMC4182436 DOI: 10.1371/journal.pone.0107640] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 08/11/2014] [Indexed: 01/05/2023] Open
Abstract
For adaptation between anaerobic, micro-aerobic and aerobic conditions Escherichia coli's metabolism and in particular its electron transport chain (ETC) is highly regulated. Although it is known that the global transcriptional regulators FNR and ArcA are involved in oxygen response it is unclear how they interplay in the regulation of ETC enzymes under micro-aerobic chemostat conditions. Also, there are diverse results which and how quinones (oxidised/reduced, ubiquinone/other quinones) are controlling the ArcBA two-component system. In the following a mathematical model of the E. coli ETC linked to basic modules for substrate uptake, fermentation product excretion and biomass formation is introduced. The kinetic modelling focusses on regulatory principles of the ETC for varying oxygen conditions in glucose-limited continuous cultures. The model is based on the balance of electron donation (glucose) and acceptance (oxygen or other acceptors). Also, it is able to account for different chemostat conditions due to changed substrate concentrations and dilution rates. The parameter identification process is divided into an estimation and a validation step based on previously published and new experimental data. The model shows that experimentally observed, qualitatively different behaviour of the ubiquinone redox state and the ArcA activity profile in the micro-aerobic range for different experimental conditions can emerge from a single network structure. The network structure features a strong feed-forward effect from the FNR regulatory system to the ArcBA regulatory system via a common control of the dehydrogenases of the ETC. The model supports the hypothesis that ubiquinone but not ubiquinol plays a key role in determining the activity of ArcBA in a glucose-limited chemostat at micro-aerobic conditions.
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Affiliation(s)
| | - Alexander Ter Beek
- Molecular Microbial Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
| | - Sonja Steinsiek
- Experimental Systems Biology, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Stefan Stagge
- Experimental Systems Biology, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - Katja Bettenbrock
- Experimental Systems Biology, Max-Planck-Institute for Dynamics of Complex Technical Systems, Magdeburg, Germany
| | - M. Joost Teixeira de Mattos
- Molecular Microbial Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
| | - Thomas Sauter
- Life Science Research Unit, Université du Luxembourg, Luxembourg, Luxembourg
| | - Oliver Sawodny
- Institute for System Dynamics, University of Stuttgart, Stuttgart, Germany
| | - Michael Ederer
- Institute for System Dynamics, University of Stuttgart, Stuttgart, Germany
- * E-mail:
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Ederer M, Steinsiek S, Stagge S, Rolfe MD, Ter Beek A, Knies D, Teixeira de Mattos MJ, Sauter T, Green J, Poole RK, Bettenbrock K, Sawodny O. A mathematical model of metabolism and regulation provides a systems-level view of how Escherichia coli responds to oxygen. Front Microbiol 2014; 5:124. [PMID: 24723921 PMCID: PMC3973912 DOI: 10.3389/fmicb.2014.00124] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 03/11/2014] [Indexed: 12/01/2022] Open
Abstract
The efficient redesign of bacteria for biotechnological purposes, such as biofuel production, waste disposal or specific biocatalytic functions, requires a quantitative systems-level understanding of energy supply, carbon, and redox metabolism. The measurement of transcript levels, metabolite concentrations and metabolic fluxes per se gives an incomplete picture. An appreciation of the interdependencies between the different measurement values is essential for systems-level understanding. Mathematical modeling has the potential to provide a coherent and quantitative description of the interplay between gene expression, metabolite concentrations, and metabolic fluxes. Escherichia coli undergoes major adaptations in central metabolism when the availability of oxygen changes. Thus, an integrated description of the oxygen response provides a benchmark of our understanding of carbon, energy, and redox metabolism. We present the first comprehensive model of the central metabolism of E. coli that describes steady-state metabolism at different levels of oxygen availability. Variables of the model are metabolite concentrations, gene expression levels, transcription factor activities, metabolic fluxes, and biomass concentration. We analyze the model with respect to the production capabilities of central metabolism of E. coli. In particular, we predict how precursor and biomass concentration are affected by product formation.
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Affiliation(s)
- Michael Ederer
- Institute for System Dynamics, University of Stuttgart Stuttgart, Germany
| | - Sonja Steinsiek
- Max Planck Institute for Dynamics of Complex Technical Systems Magdeburg, Germany
| | - Stefan Stagge
- Max Planck Institute for Dynamics of Complex Technical Systems Magdeburg, Germany
| | - Matthew D Rolfe
- Department of Molecular Biology and Biotechnology, The University of Sheffield Sheffield, UK
| | - Alexander Ter Beek
- Molecular Microbial Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam Amsterdam, Netherlands
| | - David Knies
- Institute for System Dynamics, University of Stuttgart Stuttgart, Germany
| | - M Joost Teixeira de Mattos
- Molecular Microbial Physiology, Swammerdam Institute for Life Sciences, University of Amsterdam Amsterdam, Netherlands
| | - Thomas Sauter
- Life Sciences Research Unit, Université du Luxembourg Luxembourg, Luxembourg
| | - Jeffrey Green
- Department of Molecular Biology and Biotechnology, The University of Sheffield Sheffield, UK
| | - Robert K Poole
- Department of Molecular Biology and Biotechnology, The University of Sheffield Sheffield, UK
| | - Katja Bettenbrock
- Max Planck Institute for Dynamics of Complex Technical Systems Magdeburg, Germany
| | - Oliver Sawodny
- Institute for System Dynamics, University of Stuttgart Stuttgart, Germany
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Adessi A, De Philippis R. Photosynthesis and Hydrogen Production in Purple Non Sulfur Bacteria: Fundamental and Applied Aspects. ACTA ACUST UNITED AC 2014. [DOI: 10.1007/978-94-017-8554-9_12] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
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Sevilla E, Alvarez-Ortega C, Krell T, Rojo F. The Pseudomonas putida HskA hybrid sensor kinase responds to redox signals and contributes to the adaptation of the electron transport chain composition in response to oxygen availability. ENVIRONMENTAL MICROBIOLOGY REPORTS 2013; 5:825-834. [PMID: 24249291 DOI: 10.1111/1758-2229.12083] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 06/22/2013] [Indexed: 06/02/2023]
Abstract
Pseudomonas putida has a branched aerobic electron transport that includes five terminal oxidases, each of which has different properties. The relative expression of each oxidase is carefully regulated to assemble the most suitable electron transport chain for the prevailing conditions. The HskA hybrid sensor kinase participates in this control, but the signals to which HskA responds were unknown. Here, the influence of HskA on the mRNA abundance of genes coding for all terminal oxidases and for the bc1 complex was analysed in cells growing under controlled aerobic, semiaerobic or microaerobic conditions. The results indicate that the influence of HskA on the expression of each terminal oxidase and the bc1 complex varies depending on oxygen availability. This effect was more pronounced under aerobic or semiaerobic conditions, but decreased under microaerobic conditions. The expression of hskA was regulated by oxygen availability. We show that HskA autophosphorylation is inhibited by ubiquinone but not by ubiquinol, its reduced derivative. This suggests that HskA could sense the oxidation state of the respiratory ubiquinones, which may be a key factor in HskA activity. Inactivation of hskA reduced growth rate and oxygen consumption, stressing the importance of HskA for the assembly of an efficient electron transport chain.
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Affiliation(s)
- Emma Sevilla
- Departamento de Biotecnología Microbiana, Centro Nacional de Biotecnología, CSIC, Campus UAM, Cantoblanco, 28049, Madrid, Spain
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Rex R, Bill N, Schmidt-Hohagen K, Schomburg D. Swimming in light: a large-scale computational analysis of the metabolism of Dinoroseobacter shibae. PLoS Comput Biol 2013; 9:e1003224. [PMID: 24098096 PMCID: PMC3789786 DOI: 10.1371/journal.pcbi.1003224] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Accepted: 07/31/2013] [Indexed: 01/26/2023] Open
Abstract
The Roseobacter clade is a ubiquitous group of marine α-proteobacteria. To gain insight into the versatile metabolism of this clade, we took a constraint-based approach and created a genome-scale metabolic model (iDsh827) of Dinoroseobacter shibae DFL12T. Our model is the first accounting for the energy demand of motility, the light-driven ATP generation and experimentally determined specific biomass composition. To cover a large variety of environmental conditions, as well as plasmid and single gene knock-out mutants, we simulated 391,560 different physiological states using flux balance analysis. We analyzed our results with regard to energy metabolism, validated them experimentally, and revealed a pronounced metabolic response to the availability of light. Furthermore, we introduced the energy demand of motility as an important parameter in genome-scale metabolic models. The results of our simulations also gave insight into the changing usage of the two degradation routes for dimethylsulfoniopropionate, an abundant compound in the ocean. A side product of dimethylsulfoniopropionate degradation is dimethyl sulfide, which seeds cloud formation and thus enhances the reflection of sunlight. By our exhaustive simulations, we were able to identify single-gene knock-out mutants, which show an increased production of dimethyl sulfide. In addition to the single-gene knock-out simulations we studied the effect of plasmid loss on the metabolism. Moreover, we explored the possible use of a functioning phosphofructokinase for D. shibae. The oceans are home to a large variety of microorganisms, which interact in several ways with world-wide metabolic cycles. A representative of an important group of marine bacteria called the Roseobacter clade is Dinoroseobacter shibae. This organism is known to use a variant of photosynthesis to obtain energy from light. Another feature of D. shibae and many other Roseobacters is the ability to degrade an abundant compound in the ocean called dimethylsulfoniopropionate. Importantly, one degradation pathway of dimethylsulfoniopropionate releases a side product, which affects climate by seeding cloud formation. In this work, we constructed a genome-scale metabolic model of D. shibae and carried out a detailed computational analysis of its metabolism. Our model simulates the light-harvesting capabilities of D. shibae and also accounts for the energy needed to swim. Thanks to our exhaustive simulations we were able to elucidate the effect of light on the growth of D. shibae, to study the consequences of genetic perturbations, and to identify mutants which produce more cloud-seeding compounds. Foremost, our computational results help to understand an important part of the complex processes in the ocean in greater detail. Besides, they can be a valuable guide for future wet-lab experiments.
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Affiliation(s)
- Rene Rex
- Department of Bioinformatics and Biochemistry, Technische Universität Braunschweig, Braunschweig, Germany
| | - Nelli Bill
- Department of Bioinformatics and Biochemistry, Technische Universität Braunschweig, Braunschweig, Germany
| | - Kerstin Schmidt-Hohagen
- Department of Bioinformatics and Biochemistry, Technische Universität Braunschweig, Braunschweig, Germany
| | - Dietmar Schomburg
- Department of Bioinformatics and Biochemistry, Technische Universität Braunschweig, Braunschweig, Germany
- * E-mail:
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29
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Du H, Li D, Wang Y, Wang C, Zhang D, Yang YL, Wang C. Determination of the Surface Charge Density and Temperature Dependence of Purple Membrane by Electric Force Microscopy. J Phys Chem B 2013; 117:9895-9. [DOI: 10.1021/jp403075w] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- Huiwen Du
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
- Department of Chemistry, Tsinghua University, Beijing 100084,
China
| | - Denghua Li
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
| | - Yibing Wang
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
| | - Chenxuan Wang
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
- Department of Chemistry, Tsinghua University, Beijing 100084,
China
| | - Dongdong Zhang
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
| | - Yan-lian Yang
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
| | - Chen Wang
- National Center for Nanoscience and Technology, Beijing 100190, People’s
Republic of China
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Bar-Even A, Noor E, Flamholz A, Milo R. Design and analysis of metabolic pathways supporting formatotrophic growth for electricity-dependent cultivation of microbes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2012; 1827:1039-47. [PMID: 23123556 DOI: 10.1016/j.bbabio.2012.10.013] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 10/05/2012] [Accepted: 10/25/2012] [Indexed: 11/29/2022]
Abstract
Electrosynthesis is a promising approach that enables the biological production of commodities, like fuels and fine chemicals, using renewably produced electricity. Several techniques have been proposed to mediate the transfer of electrons from the cathode to living cells. Of these, the electroproduction of formate as a mediator seems especially promising: formate is readily soluble, of low toxicity and can be produced at relatively high efficiency and at reasonable current density. While organisms that are capable of formatotrophic growth, i.e. growth on formate, exist naturally, they are generally less suitable for bulk cultivation and industrial needs. Hence, it may be helpful to engineer a model organism of industrial relevance, such as E. coli, for growth on formate. There are numerous metabolic pathways that can potentially support formatotrophic growth. Here we analyze these diverse pathways according to various criteria including biomass yield, thermodynamic favorability, chemical motive force, kinetics and the practical challenges posed by their expression. We find that the reductive glycine pathway, composed of the tetrahydrofolate system, the glycine cleavage system, serine hydroxymethyltransferase and serine deaminase, is a promising candidate to support electrosynthesis in E. coli. The approach presented here exemplifies how combining different computational approaches into a systematic analysis methodology provides assistance in redesigning metabolism. This article is part of a Special Issue entitled: Metals in Bioenergetics and Biomimetics Systems.
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Affiliation(s)
- Arren Bar-Even
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot, Israel.
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31
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Carius L, Hädicke O, Grammel H. Stepwise reduction of the culture redox potential allows the analysis of microaerobic metabolism and photosynthetic membrane synthesis inRhodospirillum rubrum. Biotechnol Bioeng 2012; 110:573-85. [DOI: 10.1002/bit.24734] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2012] [Revised: 08/29/2012] [Accepted: 09/21/2012] [Indexed: 11/09/2022]
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Sprecher BN, Gittings ME, Ludwig RA. Respiratory membrane endo-hydrogenase activity in the microaerophile Azorhizobium caulinodans is bidirectional. PLoS One 2012; 7:e36744. [PMID: 22662125 PMCID: PMC3357923 DOI: 10.1371/journal.pone.0036744] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2011] [Accepted: 04/12/2012] [Indexed: 11/19/2022] Open
Abstract
Background The microaerophilic bacterium Azorhizobium caulinodans, when fixing N2 both in pure cultures held at 20 µM dissolved O2 tension and as endosymbiont of Sesbania rostrata legume nodules, employs a novel, respiratory-membrane endo-hydrogenase to oxidize and recycle endogenous H2 produced by soluble Mo-dinitrogenase activity at the expense of O2. Methods and Findings From a bioinformatic analysis, this endo-hydrogenase is a core (6 subunit) version of (14 subunit) NADH:ubiquinone oxidoreductase (respiratory complex I). In pure A. caulinodans liquid cultures, when O2 levels are lowered to <1 µM dissolved O2 tension (true microaerobic physiology), in vivo endo-hydrogenase activity reverses and continuously evolves H2 at high rates. In essence, H+ ions then supplement scarce O2 as respiratory-membrane electron acceptor. Paradoxically, from thermodynamic considerations, such hydrogenic respiratory-membrane electron transfer need largely uncouple oxidative phosphorylation, required for growth of non-phototrophic aerobic bacteria, A. caulinodans included. Conclusions A. caulinodans in vivo endo-hydrogenase catalytic activity is bidirectional. To our knowledge, this study is the first demonstration of hydrogenic respiratory-membrane electron transfer among aerobic (non-fermentative) bacteria. When compared with O2 tolerant hydrogenases in other organisms, A. caulinodans in vivo endo-hydrogenase mediated H2 production rates (50,000 pmol 109·cells−1 min−1) are at least one-thousandfold higher. Conceivably, A. caulinodans respiratory-membrane hydrogenesis might initiate H2 crossfeeding among spatially organized bacterial populations whose individual cells adopt distinct metabolic states in response to variant O2 availability. Such organized, physiologically heterogeneous cell populations might benefit from augmented energy transduction and growth rates of the populations, considered as a whole.
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Affiliation(s)
- Brittany N. Sprecher
- Sinsheimer Laboratories, Department of Molecular, Cellular and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Margo E. Gittings
- Sinsheimer Laboratories, Department of Molecular, Cellular and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
| | - Robert A. Ludwig
- Sinsheimer Laboratories, Department of Molecular, Cellular and Developmental Biology, University of California Santa Cruz, Santa Cruz, California, United States of America
- * E-mail:
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Bar-Even A, Noor E, Milo R. A survey of carbon fixation pathways through a quantitative lens. JOURNAL OF EXPERIMENTAL BOTANY 2012; 63:2325-42. [PMID: 22200662 DOI: 10.1093/jxb/err417] [Citation(s) in RCA: 133] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
While the reductive pentose phosphate cycle is responsible for the fixation of most of the carbon in the biosphere, it has several natural substitutes. In fact, due to the characterization of three new carbon fixation pathways in the last decade, the diversity of known metabolic solutions for autotrophic growth has doubled. In this review, the different pathways are analysed and compared according to various criteria, trying to connect each of the different metabolic alternatives to suitable environments or metabolic goals. The different roles of carbon fixation are discussed; in addition to sustaining autotrophic growth it can also be used for energy conservation and as an electron sink for the recycling of reduced electron carriers. Our main focus in this review is on thermodynamic and kinetic aspects, including thermodynamically challenging reactions, the ATP requirement of each pathway, energetic constraints on carbon fixation, and factors that are expected to limit the rate of the pathways. Finally, possible metabolic structures of yet unknown carbon fixation pathways are suggested and discussed.
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Affiliation(s)
- Arren Bar-Even
- Department of Plant Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel
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Carlson RP, Oshota OJ, Taffs RL. Systems analysis of microbial adaptations to simultaneous stresses. Subcell Biochem 2012; 64:139-57. [PMID: 23080249 DOI: 10.1007/978-94-007-5055-5_7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Microbes live in multi-factorial environments and have evolved under a variety of concurrent stresses including resource scarcity. Their metabolic organization is a reflection of their evolutionary histories and, in spite of decades of research, there is still a need for improved theoretical tools to explain fundamental aspects of microbial physiology. Using ecological and economic concepts, this chapter explores a resource-ratio based theory to elucidate microbial strategies for extracting and channeling mass and energy. The theory assumes cellular fitness is maximized by allocating scarce resources in appropriate proportions to multiple stress responses. Presented case studies deconstruct metabolic networks into a complete set of minimal biochemical pathways known as elementary flux modes. An economic analysis of the elementary flux modes tabulates enzyme atomic synthesis requirements from amino acid sequences and pathway operating costs from catabolic efficiencies, permitting characterization of inherent tradeoffs between resource investment and phenotype. A set of elementary flux modes with competitive tradeoffs properties can be mathematically projected onto experimental fluxomics datasets to decompose measured phenotypes into metabolic adaptations, interpreted as cellular responses proportional to the experienced culturing stresses. The resource-ratio based method describes the experimental phenotypes with greater accuracy than other contemporary approaches and further analysis suggests the results are both statistically and biologically significant. The insight into metabolic network design principles including tradeoffs associated with concurrent stress adaptation provides a foundation for interpreting physiology as well as for rational control and engineering of medically, environmentally, and industrially relevant microbes.
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Affiliation(s)
- Ross P Carlson
- Chemical and Biological Engineering Department, Center for Biofilm Engineering, Montana State University, Bozeman, MT, 59717-3920, USA,
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Skizim NJ, Ananyev GM, Krishnan A, Dismukes GC. Metabolic pathways for photobiological hydrogen production by nitrogenase- and hydrogenase-containing unicellular cyanobacteria Cyanothece. J Biol Chem 2011; 287:2777-86. [PMID: 22128188 DOI: 10.1074/jbc.m111.302125] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Current biotechnological interest in nitrogen-fixing cyanobacteria stems from their robust respiration and capacity to produce hydrogen. Here we quantify both dark- and light-induced H(2) effluxes by Cyanothece sp. Miami BG 043511 and establish their respective origins. Dark, anoxic H(2) production occurs via hydrogenase utilizing reductant from glycolytic catabolism of carbohydrates (autofermentation). Photo-H(2) is shown to occur via nitrogenase and requires illumination of PSI, whereas production of O(2) by co-illumination of PSII is inhibitory to nitrogenase above a threshold pO(2). Carbohydrate also serves as the major source of reductant for the PSI pathway mediated via nonphotochemical reduction of the plastoquinone pool by NADH dehydrogenases type-1 and type-2 (NDH-1 and NDH-2). Redirection of this reductant flux exclusively through the proton-coupled NDH-1 by inhibition of NDH-2 with flavone increases the photo-H(2) production rate by 2-fold (at the expense of the dark-H(2) rate), due to production of additional ATP (via the proton gradient). Comparison of photobiological hydrogen rates, yields, and energy conversion efficiencies reveals opportunities for improvement.
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Affiliation(s)
- Nicholas J Skizim
- Department of Chemistry and Chemical Biology, Waksman Institute of Microbiology, Rutgers University, Piscataway, New Jersey 08854, USA
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Network identification and flux quantification of glucose metabolism in Rhodobacter sphaeroides under photoheterotrophic H(2)-producing conditions. J Bacteriol 2011; 194:274-83. [PMID: 22056932 DOI: 10.1128/jb.05624-11] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nonsulfur purple bacteria that exhibit unusual metabolic versatility can produce hydrogen gas (H(2)) using the electrons derived from metabolism of organic compounds during photoheterotrophic growth. Here, based on (13)C tracer experiments, we identified the network of glucose metabolism and quantified intracellular carbon fluxes in Rhodobacter sphaeroides KD131 grown under H(2)-producing conditions. Moreover, we investigated how the intracellular fluxes in R. sphaeroides responded to knockout mutations in hydrogenase and poly-β-hydroxybutyrate synthase genes, which led to increased H(2) yield. The relative contribution of the Entner-Doudoroff pathway and Calvin-Benson-Bassham cycle to glucose metabolism differed significantly in hydrogenase-deficient mutants, and this flux change contributed to the increased formation of the redox equivalent NADH. Disruption of hydrogenase and poly-β-hydroxybutyrate synthase resulted in a significantly increased flux through the phosphoenolpyruvate carboxykinase and a reduced flux through the malic enzyme. A remarkable increase in the flux through the tricarboxylic acid cycle, a major NADH producer, was observed for the mutant strains. The in vivo regulation of the tricarboxylic acid cycle flux in photoheterotrophic R. sphaeroides was discussed based on the measurements of in vitro enzyme activities and intracellular concentrations of NADH and NAD(+). Overall, our results provide quantitative insights into how photoheterotrophic cells manipulate the metabolic network and redistribute intracellular fluxes to generate more electrons for increased H(2) production.
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Genc S, Kurnaz IA, Ozilgen M. Astrocyte-neuron lactate shuttle may boost more ATP supply to the neuron under hypoxic conditions--in silico study supported by in vitro expression data. BMC SYSTEMS BIOLOGY 2011; 5:162. [PMID: 21995951 PMCID: PMC3202240 DOI: 10.1186/1752-0509-5-162] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2011] [Accepted: 10/13/2011] [Indexed: 12/11/2022]
Abstract
Background Neuro-glial interactions are important for normal functioning of the brain as well as brain energy metabolism. There are two major working models - in the classical view, both neurons and astrocytes can utilize glucose as the energy source through oxidative metabolism, whereas in the astrocyte-neuron lactate shuttle hypothesis (ANLSH) it is the astrocyte which can consume glucose through anaerobic glycolysis to pyruvate and then to lactate, and this lactate is secreted to the extracellular space to be taken up by the neuron for further oxidative degradation. Results In this computational study, we have included hypoxia-induced genetic regulation of these enzymes and transporters, and analyzed whether the ANLSH model can provide an advantage to either cell type in terms of supplying the energy demand. We have based this module on our own experimental analysis of hypoxia-dependent regulation of transcription of key metabolic enzymes. Using this experimentation-supported in silico modeling, we show that under both normoxic and hypoxic conditions in a given time period ANLSH model does indeed provide the neuron with more ATP than in the classical view. Conclusions Although the ANLSH is energetically more favorable for the neuron, it is not the case for the astrocyte in the long term. Considering the fact that astrocytes are more resilient to hypoxia, we would propose that there is likely a switch between the two models, based on the energy demand of the neuron, so as to maintain the survival of the neuron under hypoxic or glucose-and-oxygen-deprived conditions.
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Affiliation(s)
- Seda Genc
- Chemical Engineering Department, Yeditepe University, Istanbul, Turkey.
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Hädicke O, Grammel H, Klamt S. Metabolic network modeling of redox balancing and biohydrogen production in purple nonsulfur bacteria. BMC SYSTEMS BIOLOGY 2011; 5:150. [PMID: 21943387 PMCID: PMC3203349 DOI: 10.1186/1752-0509-5-150] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/16/2011] [Accepted: 09/25/2011] [Indexed: 02/05/2023]
Abstract
Background Purple nonsulfur bacteria (PNSB) are facultative photosynthetic bacteria and exhibit an extremely versatile metabolism. A central focus of research on PNSB dealt with the elucidation of mechanisms by which they manage to balance cellular redox under diverse conditions, in particular under photoheterotrophic growth. Results Given the complexity of the central metabolism of PNSB, metabolic modeling becomes crucial for an integrated analysis of the accumulated biological knowledge. We reconstructed a stoichiometric model capturing the central metabolism of three important representatives of PNSB (Rhodospirillum rubrum, Rhodobacter sphaeroides and Rhodopseudomonas palustris). Using flux variability analysis, the model reveals key metabolic constraints related to redox homeostasis in these bacteria. With the help of the model we can (i) give quantitative explanations for non-intuitive, partially species-specific phenomena of photoheterotrophic growth of PNSB, (ii) reproduce various quantitative experimental data, and (iii) formulate several new hypotheses. For example, model analysis of photoheterotrophic growth reveals that - despite a large number of utilizable catabolic pathways - substrate-specific biomass and CO2 yields are fixed constraints, irrespective of the assumption of optimal growth. Furthermore, our model explains quantitatively why a CO2 fixing pathway such as the Calvin cycle is required by PNSB for many substrates (even if CO2 is released). We also analyze the role of other pathways potentially involved in redox metabolism and how they affect quantitatively the required capacity of the Calvin cycle. Our model also enables us to discriminate between different acetate assimilation pathways that were proposed recently for R. sphaeroides and R. rubrum, both lacking the isocitrate lyase. Finally, we demonstrate the value of the metabolic model also for potential biotechnological applications: we examine the theoretical capabilities of PNSB for photoheterotrophic hydrogen production and identify suitable genetic interventions to increase the hydrogen yield. Conclusions Taken together, the metabolic model (i) explains various redox-related phenomena of the versatile metabolism of PNSB, (ii) delivers new hypotheses on the operation and relevance of several metabolic pathways, and (iii) holds significant potential as a tool for rational metabolic engineering of PNSB in biotechnological applications.
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Affiliation(s)
- Oliver Hädicke
- Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstrasse 1, D-39106 Magdeburg, Germany
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39
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Chang I, Heiske M, Letellier T, Wallace D, Baldi P. Modeling of mitochondria bioenergetics using a composable chemiosmotic energy transduction rate law: theory and experimental validation. PLoS One 2011; 6:e14820. [PMID: 21931590 PMCID: PMC3169640 DOI: 10.1371/journal.pone.0014820] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 05/12/2011] [Indexed: 12/28/2022] Open
Abstract
Mitochondrial bioenergetic processes are central to the production of cellular energy, and a decrease in the expression or activity of enzyme complexes responsible for these processes can result in energetic deficit that correlates with many metabolic diseases and aging. Unfortunately, existing computational models of mitochondrial bioenergetics either lack relevant kinetic descriptions of the enzyme complexes, or incorporate mechanisms too specific to a particular mitochondrial system and are thus incapable of capturing the heterogeneity associated with these complexes across different systems and system states. Here we introduce a new composable rate equation, the chemiosmotic rate law, that expresses the flux of a prototypical energy transduction complex as a function of: the saturation kinetics of the electron donor and acceptor substrates; the redox transfer potential between the complex and the substrates; and the steady-state thermodynamic force-to-flux relationship of the overall electro-chemical reaction. Modeling of bioenergetics with this rate law has several advantages: (1) it minimizes the use of arbitrary free parameters while featuring biochemically relevant parameters that can be obtained through progress curves of common enzyme kinetics protocols; (2) it is modular and can adapt to various enzyme complex arrangements for both in vivo and in vitro systems via transformation of its rate and equilibrium constants; (3) it provides a clear association between the sensitivity of the parameters of the individual complexes and the sensitivity of the system's steady-state. To validate our approach, we conduct in vitro measurements of ETC complex I, III, and IV activities using rat heart homogenates, and construct an estimation procedure for the parameter values directly from these measurements. In addition, we show the theoretical connections of our approach to the existing models, and compare the predictive accuracy of the rate law with our experimentally fitted parameters to those of existing models. Finally, we present a complete perturbation study of these parameters to reveal how they can significantly and differentially influence global flux and operational thresholds, suggesting that this modeling approach could help enable the comparative analysis of mitochondria from different systems and pathological states. The procedures and results are available in Mathematica notebooks at http://www.igb.uci.edu/tools/sb/mitochondria-modeling.html.
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Affiliation(s)
- Ivan Chang
- Department of Biomedical Engineering, University of California Irvine, Irvine, California, United States of America
- Institute of Genomic Biology, University of California Irvine, Irvine, California, United States of America
| | - Margit Heiske
- INSERM U688, University of Bordeaux-2, Bordeaux, France
| | | | - Douglas Wallace
- Department of Biochemistry, University of California Irvine, Irvine, California, United States of America
- Center for Mitochondrial and Molecular Medicine and Genetics (MAMMAG), University of California Irvine, Irvine, California, United States of America
- Department of Computer Science, University of California Irvine, Irvine, California, United States of America
| | - Pierre Baldi
- Institute of Genomic Biology, University of California Irvine, Irvine, California, United States of America
- Department of Computer Science, University of California Irvine, Irvine, California, United States of America
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Selao TT, Branca R, Chae PS, Lehtiö J, Gellman SH, Rasmussen SGF, Nordlund S, Norén A. Identification of chromatophore membrane protein complexes formed under different nitrogen availability conditions in Rhodospirillum rubrum. J Proteome Res 2011; 10:2703-14. [PMID: 21443180 DOI: 10.1021/pr100838x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The chromatophore membrane of the photosynthetic diazotroph Rhodospirillum rubrum is of vital importance for a number of central processes, including nitrogen fixation. Using a novel amphiphile, we have identified protein complexes present under different nitrogen availability conditions by the use of two-dimensional Blue Native/SDS-PAGE and NSI-LC-LTQ-Orbitrap mass spectrometry. We have identified several membrane protein complexes, including components of the ATP synthase, reaction center, light harvesting, and NADH dehydrogenase complexes. Additionally, we have identified differentially expressed proteins, such as subunits of the succinate dehydrogenase complex and other TCA cycle enzymes that are usually found in the cytosol, thus hinting at a possible association to the membrane in response to nitrogen deficiency. We propose a redox sensing mechanism that can influence the membrane subproteome in response to nitrogen availability.
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Affiliation(s)
- Tiago Toscano Selao
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
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41
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Golomysova AN, Ivanov PS. Investigation of the anaerobic metabolism of Rhodobacter capsulatus by means of a flux model. Biophysics (Nagoya-shi) 2011. [DOI: 10.1134/s000635091101009x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Jaschke PR, Saer RG, Noll S, Beatty JT. Modification of the genome of Rhodobacter sphaeroides and construction of synthetic operons. Methods Enzymol 2011; 497:519-38. [PMID: 21601102 DOI: 10.1016/b978-0-12-385075-1.00023-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The α-proteobacterium Rhodobacter sphaeroides is an exemplary model organism for the creation and study of novel protein expression systems, especially membrane protein complexes that harvest light energy to yield electrical energy. Advantages of this organism include a sequenced genome, tools for genetic engineering, a well-characterized metabolism, and a large membrane surface area when grown under hypoxic or anoxic conditions. This chapter provides a framework for the utilization of R. sphaeroides as a model organism for membrane protein expression, highlighting key advantages and shortcomings. Procedures covered in this chapter include the creation of chromosomal gene deletions, disruptions, and replacements, as well as the construction of a synthetic operon using a model promoter to induce expression of modified photosynthetic reaction center proteins for structural and functional analysis.
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Affiliation(s)
- Paul R Jaschke
- Department of Microbiology and Immunology, University of British Columbia, Life Sciences Centre, Vancouver, British Columbia, Canada
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Wu J, Bauer CE. RegB kinase activity is controlled in part by monitoring the ratio of oxidized to reduced ubiquinones in the ubiquinone pool. mBio 2010; 1:e00272-10. [PMID: 21157513 PMCID: PMC3000548 DOI: 10.1128/mbio.00272-10] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Accepted: 11/10/2010] [Indexed: 01/08/2023] Open
Abstract
RegB is a membrane-spanning sensor kinase responsible for redox regulation of a wide variety of metabolic processes in numerous proteobacterial species. Here we show that full-length RegB purified from Escherichia coli membranes contains bound ubiquinone. Four conserved residues in the membrane-spanning domain of RegB are shown to have important roles in ubiquinone binding in vitro and redox sensing in vivo. Isothermal titration calorimetry measurements, coupled with kinase assays under oxidizing and reducing conditions, indicate that RegB weakly binds both oxidized ubiquinone and reduced ubiquinone (ubiquinol) with nearly equal affinity and that oxidized ubiquinone inhibits kinase activity without promoting a redox reaction. We propose a model in which ubiquinone/ubiquinol bound to RegB readily equilibrates with ubiquinones/ubiquinols in the membrane, allowing the kinase activity to be tuned by the redox state of the ubiquinone pool. This noncatalytic role of ubiquinone in controlling RegB activity is distinct from that of other known ubiquinone-binding proteins, which use ubiquinone as an electron donor or acceptor.
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Affiliation(s)
- Jiang Wu
- Department of Molecular and Cellular Biochemistry, Indiana University, Bloomington, Indiana, USA
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Bridging the gap: linking molecular simulations and systemic descriptions of cellular compartments. PLoS One 2010; 5:e14070. [PMID: 21124924 PMCID: PMC2989909 DOI: 10.1371/journal.pone.0014070] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2010] [Accepted: 10/21/2010] [Indexed: 12/31/2022] Open
Abstract
Metabolic processes in biological cells are commonly either characterized at the level of individual enzymes and metabolites or at the network level. Often these two paradigms are considered as mutually exclusive because concepts from neither side are suited to describe the complete range of scales. Additionally, when modeling metabolic or regulatory cellular systems, often a large fraction of the required kinetic parameters are unknown. This even applies to such simple and extensively studied systems like the photosynthetic apparatus of purple bacteria. Using the chromatophore vesicles of Rhodobacter sphaeroides as a model system, we show that a consistent kinetic model emerges when fitting the dynamics of a molecular stochastic simulation to a set of time dependent experiments even though about two thirds of the kinetic parameters in this system are not known from experiment. Those kinetic parameters that were previously known all came out in the expected range. The simulation model was built from independent protein units composed of elementary reactions processing single metabolites. This pools-and-proteins approach naturally compiles the wealth of available molecular biological data into a systemic model and can easily be extended to describe other systems by adding new protein or nucleic acid types. The automated parameter optimization, performed with an evolutionary algorithm, reveals the sensitivity of the model to the value of each parameter and the relative importances of the experiments used. Such an analysis identifies the crucial system parameters and guides the setup of new experiments that would add most knowledge for a systemic understanding of cellular compartments. The successful combination of the molecular model and the systemic parametrization presented here on the example of the simple machinery for bacterial photosynthesis shows that it is actually possible to combine molecular and systemic modeling. This framework can now straightforwardly be applied to other currently less well characterized but biologically more relevant systems.
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Beyond the genome: functional studies of phototrophic sulfur oxidation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010. [PMID: 20532738 DOI: 10.1007/978-1-4419-1528-3_7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register]
Abstract
The increasing availability of complete genomic sequences for cultured phototrophic bacteria and assembled metagenomes from environments dominated by phototrophs has reinforced the need for a "post-genomic" analytical effort to test models of cellular structure and function proposed from genomic data. Comparative genomics has produced a testable model for pathways of sulfur compound oxidation in the phototrophic bacteria. In the case of sulfide, two enzymes are predicted to oxidize sulfide: sulfide:quinone oxidoreductase and flavocytochrome c sulfide dehydrogenase. However, these models do not predict which enzyme is important under what conditions. In Chlorobaculum tepidum, a model green sulfur bacterium, a combination of genetics and physiological analysis of mutant strains has led to the realization that this organism contains at least two active sulfide:quinone oxidoreductases and that there is significant interaction between sulfide oxidation and light harvesting. In the case of elemental sulfur, an organothiol intermediate of unknown structure has been proposed to activate elemental sulfur for transport into the cytoplasm where it can be oxidized or assimilated, and recent approaches using classical metabolite analysis have begun to shed light on this issue both in C. tepidum and the purple sulfur bacterium Allochromatium vinosum.
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Bína D, Litvín R, Vácha F. Absorbance changes accompanying the fast fluorescence induction in the purple bacterium Rhodobacter sphaeroides. PHOTOSYNTHESIS RESEARCH 2010; 105:115-121. [PMID: 20574750 DOI: 10.1007/s11120-010-9569-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2010] [Accepted: 05/30/2010] [Indexed: 05/29/2023]
Abstract
The authors present a study of the fluorescence and absorbance transients occurring in whole cells of purple nonsulfur bacterium Rhodobacter sphaeroides on the millisecond timescale under pulsed actinic illumination. The fluorescence induction curve is interpreted in terms of combination of effects of redox changes in the reaction center and the membrane potential. The results of this study support the view that the membrane potential act predominantly to increase the fluorescence yield. Advantages of the pulsed actinic illumination for study of the operation of the electron transport chain in vivo are discussed.
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Affiliation(s)
- David Bína
- Biology Centre ASCR, v.v.i, Institute of Plant Molecular Biology and Faculty of Science, University of South Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic
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Heinemann M, Sauer U. Systems biology of microbial metabolism. Curr Opin Microbiol 2010; 13:337-43. [PMID: 20219420 DOI: 10.1016/j.mib.2010.02.005] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2010] [Accepted: 02/13/2010] [Indexed: 12/20/2022]
Abstract
One current challenge in metabolic systems biology is to map out the regulation networks that control metabolism. From progress in this area, we conclude that non-transcriptional mechanisms (e.g. metabolite-protein interactions and protein phosphorylation) are highly relevant in actually controlling metabolic function. Furthermore, recent results highlight more functions of enzymes and metabolites than currently appreciated in genome-scale metabolic reconstructions, thereby adding another level of complexity. Combining experimental analyses and modeling efforts we are also beginning to understand how metabolic behavior emerges. Particularly, we recognize that metabolism is not simply a dull workhorse process but rather takes very active control of itself and other cellular processes, rendering true system-level understanding of metabolism possibly more difficult than for other cellular systems.
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Affiliation(s)
- Matthias Heinemann
- ETH Zurich, Institute of Molecular Systems Biology, Wolfgang-Pauli-Str. 16, 8093 Zurich, Switzerland.
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Zeiger L, Grammel H. Model-based high cell density cultivation of Rhodospirillum rubrum under respiratory dark conditions. Biotechnol Bioeng 2010; 105:729-39. [PMID: 19882736 DOI: 10.1002/bit.22589] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The potential of facultative photosynthetic bacteria as producers of photosynthetic pigments, vitamins, coenzymes and other valuable products has been recognized for decades. However, mass cultivation under photosynthetic conditions is generally inefficient due to the inevitable limitation of light supply when cell densities become very high. The previous development of a new cultivation process for maximal expression of photosynthetic genes under semi-aerobic dark conditions in common bioreactors offers a new perspective for utilizing the facultative photosynthetic bacterium Rhodospirillum rubrum for large-scale applications. Based on this cultivation system, the present study aimed in determining the maximal achievable cell density of R. rubrum in a bioreactor, thereby providing a major milestone on the way to industrial bioprocesses. As a starting point, we focus on aerobic growth due to higher growth rates and more facile process control under this condition, with the option to extend the process by an anaerobic production phase. Process design and optimization were supported by an unstructured computational process model, based on mixed-substrate kinetics. Key parameters for growth and process control were determined in shake-flask experiments or estimated by simulation studies. For fed-batch cultivation, a computer-controlled exponential feed algorithm in combination with a pH-stat element was implemented. As a result, a maximal cell density of 59 g cell dry weight (CDW) L(-1) was obtained, representing so far not attainable cell densities for photosynthetic bacteria. The applied exponential fed-batch methodology therefore enters a range which is commonly employed for industrial applications with microbial cells. The biochemical analysis of high cell density cultures revealed metabolic imbalances, such as the accumulation and excretion of tetrapyrrole intermediates of the bacteriochlorophyll biosynthetic pathway.
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Affiliation(s)
- Lisa Zeiger
- Max Planck Institute for Dynamics of Complex Technical Systems, Sandtorstr. 1, 39106 Magdeburg, Germany.
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Spring S, Lünsdorf H, Fuchs BM, Tindall BJ. The photosynthetic apparatus and its regulation in the aerobic gammaproteobacterium Congregibacter litoralis gen. nov., sp. nov. PLoS One 2009; 4:e4866. [PMID: 19287491 PMCID: PMC2654016 DOI: 10.1371/journal.pone.0004866] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2008] [Accepted: 02/16/2009] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND There is accumulating evidence that in some marine environments aerobic bacteriochlorophyll a-producing bacteria represent a significant part of the microbial population. The interaction of photosynthesis and carbon metabolism in these interesting bacteria is still largely unknown and requires further investigation in order to estimate their contribution to the marine carbon cycle. METHODOLOGY/PRINCIPAL FINDINGS Here, we analyzed the structure, composition and regulation of the photosynthetic apparatus in the obligately aerobic marine gammaproteobacterium KT71(T). Photoheterotrophically grown cells were characterized by a poorly developed lamellar intracytoplasmic membrane system, a type 1 light-harvesting antenna complex and a photosynthetic reaction center associated with a tetraheme cytochrome c. The only photosynthetic pigments produced were bacteriochlorophyll a and spirilloxanthin. Under semiaerobic conditions KT71(T) cells expressing a photosynthetic apparatus showed a light-dependent increase of growth yield in the range of 1.3-2.5 fold. The expression level of the photosynthetic apparatus depended largely on the utilized substrate, the intermediary carbon metabolism and oxygen tension. In addition, pigment synthesis was strongly influenced by light, with blue light exerting the most significant effect, implicating that proteins containing a BLUF domain may be involved in regulation of the photosynthetic apparatus. Several phenotypic traits in KT71(T) could be identified that correlated with the assumed redox state of growing cells and thus could be used to monitor the cellular redox state under various incubation conditions. CONCLUSIONS/SIGNIFICANCE In a hypothetical model that explains the regulation of the photosynthetic apparatus in strain KT71(T) we propose that the expression of photosynthesis genes depends on the cellular redox state and is maximal under conditions that allow a balanced membrane redox state. So far, bacteria capable of an obligately aerobic, photosynthetic metabolism constitute a unique phenotype within the class Gammaproteobacteria, so that it is justified to propose a new genus and species, Congregibacter litoralis gen. nov, sp. nov., represented by the type strain KT71(T) ( = DSM 17192(T) = NBRC 104960(T)).
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Affiliation(s)
- Stefan Spring
- Deutsche Sammlung von Mikroorganismen und Zellkulturen, Braunschweig, Germany.
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50
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Grammel H, Klamt S, Ghosh R, Gilles E. Systems-level analysis of redox signaling in Rhodospirillum rubrum. J Biotechnol 2008. [DOI: 10.1016/j.jbiotec.2008.07.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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