The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Péter Maróti - One of the best experts on this subject based on the ideXlab platform.
-
Photoprotection in intact cells of Photosynthetic Bacteria: quenching of bacteriochlorophyll fluorescence by carotenoid triplets
Photosynthesis Research, 2017Co-Authors: Gábor Sipka, Péter MarótiAbstract:Upon high light excitation in Photosynthetic Bacteria, various triplet states of pigments can accumulate leading to harmful effects. Here, the generation and lifetime of flash-induced carotenoid triplets (3Car) have been studied by observation of the quenching of bacteriochlorophyll (BChl) fluorescence in different strains of Photosynthetic Bacteria including Rvx. gelatinosus (anaerobic and semianaerobic), Rsp. rubrum, Thio. roseopersicina, Rba. sphaeroides 2.4.1 and carotenoid- and cytochrome-deficient mutants Rba. sphaeroides Ga, R-26, and cycA, respectively. The following results were obtained: (1) 3Car quenching is observed during and not exclusively after the photochemical rise of the fluorescence yield of BChl indicating that the charge separation in the reaction center (RC) and the carotenoid triplet formation are not consecutive but parallel processes. (2) The photoprotective function of 3Car is not limited to the RC only and can be described by a model in which the carotenoids are distributed in the lake of the BChl pigments. (3) The observed lifetime of 3Car in intact cells is the weighted average of the lifetimes of the carotenoids with various numbers of conjugated double bonds in the Bacterial strain. (4) The lifetime of 3Car measured in the light is significantly shorter (1–2 μs) than that measured in the dark (2–10 μs). The difference reveals the importance of the dynamics of 3Car before relaxation. The results will be discussed not only in terms of energy levels of the 3Car but also in terms of the kinetics of transitions among different sublevels in the excited triplet state of the carotenoid.
-
Stoichiometry and kinetics of mercury uptake by Photosynthetic Bacteria
Photosynthesis Research, 2017Co-Authors: Gábor Sipka, Péter MarótiAbstract:Mercury adsorption on the cell surface and intracellular uptake by Bacteria represent the key first step in the production and accumulation of highly toxic mercury in living organisms. In this work, the biophysical characteristics of mercury bioaccumulation are studied in intact cells of Photosynthetic Bacteria by use of analytical (dithizone) assay and physiological Photosynthetic markers (pigment content, fluorescence induction, and membrane potential) to determine the amount of mercury ions bound to the cell surface and taken up by the cell. It is shown that the Hg(II) uptake mechanism (1) has two kinetically distinguishable components, (2) includes co-opted influx through heavy metal transporters since the slow component is inhibited by Ca^2+ channel blockers, (3) shows complex pH dependence demonstrating the competition of ligand binding of Hg(II) ions with H^+ ions (low pH) and high tendency of complex formation of Hg(II) with hydroxyl ions (high pH), and (4) is not a passive but an energy-dependent process as evidenced by light activation and inhibition by protonophore. Photosynthetic Bacteria can accumulate Hg(II) in amounts much (about 10^5) greater than their own masses by well-defined strong and weak binding sites with equilibrium binding constants in the range of 1 (μM)^−1 and 1 (mM)^−1, respectively. The strong binding sites are attributed to sulfhydryl groups as the uptake is blocked by use of sulfhydryl modifying agents and their number is much (two orders of magnitude) smaller than the number of weak binding sites. Biofilms developed by some Bacteria (e.g., Rvx. gelatinosus ) increase the mercury binding capacity further by a factor of about five. Photosynthetic Bacteria in the light act as a sponge of Hg(II) and can be potentially used for biomonitoring and bioremediation of mercury-contaminated aqueous cultures.
Gábor Sipka - One of the best experts on this subject based on the ideXlab platform.
-
Photoprotection in intact cells of Photosynthetic Bacteria: quenching of bacteriochlorophyll fluorescence by carotenoid triplets
Photosynthesis Research, 2017Co-Authors: Gábor Sipka, Péter MarótiAbstract:Upon high light excitation in Photosynthetic Bacteria, various triplet states of pigments can accumulate leading to harmful effects. Here, the generation and lifetime of flash-induced carotenoid triplets (3Car) have been studied by observation of the quenching of bacteriochlorophyll (BChl) fluorescence in different strains of Photosynthetic Bacteria including Rvx. gelatinosus (anaerobic and semianaerobic), Rsp. rubrum, Thio. roseopersicina, Rba. sphaeroides 2.4.1 and carotenoid- and cytochrome-deficient mutants Rba. sphaeroides Ga, R-26, and cycA, respectively. The following results were obtained: (1) 3Car quenching is observed during and not exclusively after the photochemical rise of the fluorescence yield of BChl indicating that the charge separation in the reaction center (RC) and the carotenoid triplet formation are not consecutive but parallel processes. (2) The photoprotective function of 3Car is not limited to the RC only and can be described by a model in which the carotenoids are distributed in the lake of the BChl pigments. (3) The observed lifetime of 3Car in intact cells is the weighted average of the lifetimes of the carotenoids with various numbers of conjugated double bonds in the Bacterial strain. (4) The lifetime of 3Car measured in the light is significantly shorter (1–2 μs) than that measured in the dark (2–10 μs). The difference reveals the importance of the dynamics of 3Car before relaxation. The results will be discussed not only in terms of energy levels of the 3Car but also in terms of the kinetics of transitions among different sublevels in the excited triplet state of the carotenoid.
-
Stoichiometry and kinetics of mercury uptake by Photosynthetic Bacteria
Photosynthesis Research, 2017Co-Authors: Gábor Sipka, Péter MarótiAbstract:Mercury adsorption on the cell surface and intracellular uptake by Bacteria represent the key first step in the production and accumulation of highly toxic mercury in living organisms. In this work, the biophysical characteristics of mercury bioaccumulation are studied in intact cells of Photosynthetic Bacteria by use of analytical (dithizone) assay and physiological Photosynthetic markers (pigment content, fluorescence induction, and membrane potential) to determine the amount of mercury ions bound to the cell surface and taken up by the cell. It is shown that the Hg(II) uptake mechanism (1) has two kinetically distinguishable components, (2) includes co-opted influx through heavy metal transporters since the slow component is inhibited by Ca^2+ channel blockers, (3) shows complex pH dependence demonstrating the competition of ligand binding of Hg(II) ions with H^+ ions (low pH) and high tendency of complex formation of Hg(II) with hydroxyl ions (high pH), and (4) is not a passive but an energy-dependent process as evidenced by light activation and inhibition by protonophore. Photosynthetic Bacteria can accumulate Hg(II) in amounts much (about 10^5) greater than their own masses by well-defined strong and weak binding sites with equilibrium binding constants in the range of 1 (μM)^−1 and 1 (mM)^−1, respectively. The strong binding sites are attributed to sulfhydryl groups as the uptake is blocked by use of sulfhydryl modifying agents and their number is much (two orders of magnitude) smaller than the number of weak binding sites. Biofilms developed by some Bacteria (e.g., Rvx. gelatinosus ) increase the mercury binding capacity further by a factor of about five. Photosynthetic Bacteria in the light act as a sponge of Hg(II) and can be potentially used for biomonitoring and bioremediation of mercury-contaminated aqueous cultures.
Patrick C Hallenbeck - One of the best experts on this subject based on the ideXlab platform.
-
recent advances in hydrogen production by Photosynthetic Bacteria
International Journal of Hydrogen Energy, 2016Co-Authors: Patrick C HallenbeckAbstract:Abstract The Photosynthetic Bacteria have a very versatile metabolic repertoire and have been known for decades to produce hydrogen during photofermentative growth. Here, recent advances in hydrogen production by these organisms are reviewed and future directions highlighted. Often used as a second stage in two stage hydrogen production processes; first stage fermentative sugar to hydrogen and organic acids; second stage, organic acids to hydrogen, recent studies have highlighted their ability to directly convert sugars to hydrogen. Several studies have attempted to optimize a single stage batch process and these, and a study with continuous cultures have shown that yields approaching 9 mol H2/mol glucose can be obtained. One of the drawbacks of this system is the dependency on light, necessitating the use of photobioreactors, thus potentially greatly adding to the cost of such a system. In another approach which avoids the use of light energy, microaerobic fermentation of organic acids to hydrogen, driven by limited oxidative phosphorylation has been demonstrated in principle. Further advances will probably require the use of metabolic engineering and more sophisticated process controls in order to achieve higher stoichiometries, approaches that might be applied to other, light dependent, hydrogen production process by these organisms.
Robert E Blankenship - One of the best experts on this subject based on the ideXlab platform.
-
Chlorosome antenna complexes from green Photosynthetic Bacteria
Photosynthesis Research, 2013Co-Authors: Robert E BlankenshipAbstract:Chlorosomes are the distinguishing light-harvesting antenna complexes that are found in green Photosynthetic Bacteria. They contain bacteriochlorophyll (BChl) c , d , e in natural organisms, and recently through mutation, BChl f , as their principal light-harvesting pigments. In chlorosomes, these pigments self-assemble into large supramolecular structures that are enclosed inside a lipid monolayer to form an ellipsoid. The pigment assembly is dictated mostly by pigment–pigment interactions as opposed to protein–pigment interactions. On the bottom face of the chlorosome, the CsmA protein aggregates into a paracrystalline baseplate with BChl a , and serves as the interface to the next energy acceptor in the system. The exceptional light-harvesting ability at very low light conditions of chlorosomes has made them an attractive subject of study for both basic and applied science. This review, incorporating recent advancements, considers several important aspects of chlorosomes: pigment biosynthesis, organization of pigments and proteins, spectroscopic properties, and applications to bio-hybrid and bio-inspired devices.
-
anoxygenic Photosynthetic Bacteria
1995Co-Authors: Robert E Blankenship, Michael T Madigan, Carl E BauerAbstract:Part 1 Taxonomy, Physiology and Ecology: 1. Taxonomy and Physiology of Phototrophic Purple Bacteria and Green Sulphur Bacteria J.F. Imhoff. 2. Taxonomy, Physiology and Ecology of HelioBacteria M.T. Madigan, J.G. Ormerod. 3. Taxonomy and Physiology of Filamentous Anoxygenic Phototrophs B.K. Pierson, R.W. Castenholz. 4. Ecology of Phototrophic Sulfur Bacteria H. Van Gemerden, J. Mas. 5. Ecology of Thermophilic Anoxygenic Phototrophs R.W. Castenholz, B.K. Pierson. 6. Aerobic Anoxygenic Phototrophs K. Shimada. 7. Bacteriochlorophyll-Containing Rhizobium Species D.E. Fleischman, et al. Part 2 Molecular Structure and Biosynthesis of Pigments and Cofactors: 8. Biosynthesis and Structures of the Bacteriochlorophylls M.O. Senge, K.M. Smith. 9. Biosynthesis and Structures of Porphyrins and Hemes S.I. Beale. 10. Lipids, Quinones and Fatty Acids of Anoxygenic Phototrophic Bacteria J.M. Imhoff, U. Bias-Imhoff. Part 3 Membrane and Cell Wall Architecture and Organization: 11. Anoxygenic Phototrophic Bacteria: Model Organisms for Studies on Cell Wall Macromolecules J. Weckesser, et al. 12. Structure, Molecular Organization, and Biosynthesis of Membranes of Purple Bacteria G. Drews, J.R. Golecki. 13. Membranes and Chlorosomes of Green Bacteria: Structure, Composition and Development J. Oelze, J.R. Golecki. 14. Organization of Electron Transfer Components and Supercomplexes A. Vermeglio, et al. Part 4 Antenna Structure and Function: 15. Theory of Electronic Energy Transfer W.S. Struve. 16. Structure and Organization of Purple Bacterial Antenna Complexes H. Zuber, R.J. Cogdell. 17. Kinetics of Excitation Transfer and Trapping in Purple Bacteria V. Sundstrom, R. van Grondelle. 18. Singlet Energy Transfer from Carotenoids to Bacteriochlorophylls H.A. Frank, R.L. Christensen. 19. Coupling of Antennas to Reaction Centres A. Freiberg. 20. Antenna Complexes from Green Photosynthetic Bacteria R.E. Blankenship, et al. 21. Structure-Function Relationships in Core Light-Harvesting Complexes (LHI) as Determined by Characterization of the Structural Subunit and by Reconstitution Experiments P.A. Loach, P.S. Parkes-Loach. 22. Genetic Manipulation of the Antenna Complexes of Purple Bacteria C.N. Hunter. Part 5 Reaction Centre Structure, Electron and Proton Transfer Pathways: 23. The Structures of Photosynthetic Reaction Centres from Purple Bacteria as Revealed by X-Ray Crystallography C.R.D. Lancaster, et al. 24. The Pathway, Kinetics and Thermodynamics of Electron Transfer in Wild Type and Mutant Reaction Centres of Purple Nonsulfur Bacteria N.W. Woodbury, J.P. Allen. 25. Theoretical Analyses of Electron-Transfer Reactions W.W. Parson, A. Warshel. 26. Proton-Coupled Electron Transfer Reactions of QB in Reaction Centers from Photosynthetic Bacteria M.Y. Okamura, G. Feher. (Part contents).
-
antenna complexes from green Photosynthetic Bacteria
1995Co-Authors: Robert E Blankenship, John M. Olson, Mette MillerAbstract:Green Photosynthetic Bacteria contain unique peripheral antenna complexes known as chiorosomes. Chiorosome complexes are optimized for light collection at low levels. The chlorosome is composed of large amounts of pigment and relatively little protein. The pigments consist principally of bacteriochiorophylls c, d or e plus carotenoids, along with small amounts of bacteriochlorophyll a. The bacteriochlorophylls c, d or e are organized into pigment oligomers with relatively little or no involvement of protein in determining the pigment arrangement. The bacteriochlorophyll a is associated with a protein as a pigment-protein complex. Additional membrane-associated antenna complexes are energy transfer intermediates between the chlorosome and the reaction center. These include the Fenna-Matthews-Olson protein in the green sulfur Bacteria, and integral membrane antenna complexes similar to the purple Bacterial LHI complex in the green nonsulfur Bacteria. The green sulfur Bacteria antenna system is regulated by redox potential, so that excitations are efficiently quenched at high redox potentials and never reach the reaction center. This regulation is mediated by quinone molecules that are localized in the chiorosome complex and is thought to protect the cell from light-induced superoxide formation under conditions of transient oxygen exposure.
Jun Miyake - One of the best experts on this subject based on the ideXlab platform.
-
Evaluating a time-delay of hydrogen production quantitatively in Photosynthetic Bacteria for stabilizing intermittency
Research on Chemical Intermediates, 2016Co-Authors: Kota Tanaka, Saki Okamura, Ken Shibata, Naoki Ikenaga, Nobuyuki Tanaka, Kazumi Hakamada, Jun MiyakeAbstract:Renewable energy is regarded as a clean energy source but has some problems, one of which is intermittency. To reduce this, the time-delay of hydrogen production by Photosynthetic Bacteria can be effective. In this study, we qualitatively evaluated the time-delay of hydrogen production by Photosynthetic Bacteria under various irradiation conditions, and we also quantitatively evaluated it by fitting the experimental data and the hydrogen production model with a genetic algorithm. As a result of model fitting, we found that the relationship between the lengths of the optimized time-delay of hydrogen production by Photosynthetic Bacteria and the amount of light irradiation is linear. And we also found that the time-delay of hydrogen production by Photosynthetic Bacteria had an upper limit under low light intensity. We have suggested the existence of an energy store mechanism in Photosynthetic Bacteria.
-
re evaluation of hydrogen productivity from acetate by some Photosynthetic Bacteria
International Journal of Hydrogen Energy, 2008Co-Authors: Yasuo Asada, Mitsutaka Ohsawa, Yuichiro Nagai, Katsuhiro Ishimi, Makoto Fukatsu, Akihiro Hideno, Tatsuki Wakayama, Jun MiyakeAbstract:Abstract In order to use Photosynthetic Bacteria for efficient hydrogen production after anaerobic hydrogen and acetate fermentation, hydrogen-producing activity from acetate by agar-immobilized Photosynthetic Bacteria was evaluated under light-illuminated conditions. Among the tested 5 strains, Rhodobacter sphaeroides RV gave similar rate of hydrogen production as the case of lactate, and the yield was as high as 2.65–2.81 mol of hydrogen per mol of acetate consumed. R. sphaeroides IL106 gave the highest yield of 3.03 mol of hydrogen per acetate when acetate concentration was low.
