The Experts below are selected from a list of 435 Experts worldwide ranked by ideXlab platform

Thomas E. Hanson - One of the best experts on this subject based on the ideXlab platform.

  • insights into the mineralogy and surface chemistry of extracellular biogenic s 0 globules produced by Chlorobaculum tepidum
    Frontiers in Microbiology, 2019
    Co-Authors: Cassandra L Marnocha, Thomas E. Hanson, Shannon Modla, Deborah H Powell, Chandran R. Sabanayagam, Andrew S. Steele, Pauline Henri, Samuel M Webb, Clara S Chan
    Abstract:

    Elemental sulfur (S0) is produced and degraded by phylogenetically diverse groups of microorganisms. For Chlorobaculum tepidum, an anoxygenic phototroph, sulfide is oxidized to produce extracellular S0 globules, which can be further oxidized to sulfate. While some sulfur-oxidizing bacteria (e.g., Allochromatium vinosum) are also capable of growth on commercial S0 as an electron donor, C. tepidum is not. Even colloidal sulfur sols, which appear indistinguishable from biogenic globules, do not support the growth of C. tepidum. Here, we investigate the properties that make biogenic S0 globules distinct from abiotic forms of S0. We found that S0 globules produced by C. tepidum and abiotic S0 sols are quite similar in terms of mineralogy and material properties, but the two are distinguished primarily by the properties of their surfaces. C. tepidum's globules are enveloped by a layer of organics (protein and polysaccharides), which results in a surface that is fundamentally different from that of abiotic S0 sols. The organic coating on the globules appears to slow the aging and crystallization of amorphous sulfur, perhaps providing an extended window of time for microbes in the environment to access the more labile forms of sulfur as needed. Overall, our results suggest that the surface of biogenic S0 globules may be key to cell-sulfur interactions and the reactivity of biogenic S0 in the environment.

  • Insights Into the Mineralogy and Surface Chemistry of Extracellular Biogenic S0 Globules Produced by Chlorobaculum tepidum
    Frontiers Media S.A., 2019
    Co-Authors: Thomas E. Hanson, Shannon Modla, Cassandra L Marnocha, Deborah H Powell, Chandran R. Sabanayagam, Pauline A. Henri, Andrew S. Steele
    Abstract:

    Elemental sulfur (S0) is produced and degraded by phylogenetically diverse groups of microorganisms. For Chlorobaculum tepidum, an anoxygenic phototroph, sulfide is oxidized to produce extracellular S0 globules, which can be further oxidized to sulfate. While some sulfur-oxidizing bacteria (e.g., Allochromatium vinosum) are also capable of growth on commercial S0 as an electron donor, C. tepidum is not. Even colloidal sulfur sols, which appear indistinguishable from biogenic globules, do not support the growth of C. tepidum. Here, we investigate the properties that make biogenic S0 globules distinct from abiotic forms of S0. We found that S0 globules produced by C. tepidum and abiotic S0 sols are quite similar in terms of mineralogy and material properties, but the two are distinguished primarily by the properties of their surfaces. C. tepidum’s globules are enveloped by a layer of organics (protein and polysaccharides), which results in a surface that is fundamentally different from that of abiotic S0 sols. The organic coating on the globules appears to slow the aging and crystallization of amorphous sulfur, perhaps providing an extended window of time for microbes in the environment to access the more labile forms of sulfur as needed. Overall, our results suggest that the surface of biogenic S0 globules may be key to cell–sulfur interactions and the reactivity of biogenic S0 in the environment

  • differential rna sequencing implicates sulfide as the master regulator of s 0 metabolism in Chlorobaculum tepidum and other green sulfur bacteria
    Applied and Environmental Microbiology, 2017
    Co-Authors: Thomas E. Hanson, Jacob M Hilzinger, Vidhyavathi Raman, Kevin E Shuman, Brian J Eddie
    Abstract:

    The green sulfur bacteria (Chlorobiaceae) are anaerobes that use electrons from reduced sulfur compounds (sulfide, S0, and thiosulfate) as electron donors for photoautotrophic growth. Chlorobaculum tepidum, the model system for the Chlorobiaceae, both produces and consumes extracellular S0 globules depending on the availability of sulfide in the environment. These physiological changes imply significant changes in gene regulation, which has been observed when sulfide is added to Cba. tepidum growing on thiosulfate. However, the underlying mechanisms driving these gene expression changes, i.e., the specific regulators and promoter elements involved, have not yet been defined. Here, differential RNA sequencing (dRNA-seq) was used to globally identify transcript start sites (TSS) that were present during growth on sulfide, biogenic S0, and thiosulfate as sole electron donors. TSS positions were used in combination with RNA-seq data from cultures growing on these same electron donors to identify both basal promoter elements and motifs associated with electron donor-dependent transcriptional regulation. These motifs were conserved across homologous Chlorobiaceae promoters. Two lines of evidence suggest that sulfide-mediated repression is the dominant regulatory mode in Cba. tepidum First, motifs associated with genes regulated by sulfide overlap key basal promoter elements. Second, deletion of the Cba. tepidum1277 (CT1277) gene, encoding a putative regulatory protein, leads to constitutive overexpression of the sulfide:quinone oxidoreductase CT1087 in the absence of sulfide. The results suggest that sulfide is the master regulator of sulfur metabolism in Cba. tepidum and the Chlorobiaceae Finally, the identification of basal promoter elements with differing strengths will further the development of synthetic biology in Cba. tepidum and perhaps other ChlorobiaceaeIMPORTANCE Elemental sulfur is a key intermediate in biogeochemical sulfur cycling. The photoautotrophic green sulfur bacterium Chlorobaculum tepidum either produces or consumes elemental sulfur depending on the availability of sulfide in the environment. Our results reveal transcriptional dynamics of Chlorobaculum tepidum on elemental sulfur and increase our understanding of the mechanisms of transcriptional regulation governing growth on different reduced sulfur compounds. This report identifies genes and sequence motifs that likely play significant roles in the production and consumption of elemental sulfur. Beyond this focused impact, this report paves the way for the development of synthetic biology in Chlorobaculum tepidum and other Chlorobiaceae by providing a comprehensive identification of promoter elements for control of gene expression, a key element of strain engineering.

  • drna seq implicates sulfide as master regulator of s 0 metabolism in Chlorobaculum tepidum and other green sulfur bacteria
    bioRxiv, 2017
    Co-Authors: Jacob M Hilzinger, Vidhyavathi Raman, Kevin E Shuman, Brian J Eddie, Thomas E. Hanson
    Abstract:

    The green sulfur bacteria (Chlorobiaceae) are anaerobes that use electrons from reduced sulfur compounds (sulfide, S(0), and thiosulfate) as electron donors for photoautotrophic growth. Chlorobaculum tepidum, the model system for the Chlorobiaceae, both produces and consumes extracellular S(0) globules depending on the availability of sulfide in the environment. These physiological changes imply significant changes in gene regulation, which has been observed when sulfide is added to Cba. tepidum growing on thiosulfate. However, the underlying mechanisms driving these gene expression changes, i.e. specific regulators and promoter elements involved, have not yet been defined. Here, differential RNA-seq (dRNA-seq) was used to globally identify transcript start sites (TSS) that were present during growth on sulfide, biogenic S(0), and thiosulfate as sole electron donors. TSS positions were used in combination with RNA-seq data from cultures growing on these same electron donors to identify both basal promoter elements and motifs associated with electron donor dependent transcriptional regulation. These motifs were conserved across homologous Chlorobiaceae promoters. Two lines of evidence suggest that sulfide mediated repression is the dominant regulatory mode in Cba. tepidum. First, motifs associated with genes regulated by sulfide overlap key basal promoter elements. Second, deletion of the gene CT1277, encoding a putative regulatory protein, leads to constitutive over-expression of the sulfide:quinone oxidoreductase CT1087 in the absence of sulfide. The results suggest that sulfide is the master regulator of sulfur metabolism in Cba. tepidum and the Chlorobiaceae. Finally, the identification of basal promoter elements with differing strengths will further the development of synthetic biology in Cba. tepidum and perhaps other Chlorobiaceae.

  • Chlorobaculum tepidum modulates amino acid composition in response to energy availability as revealed by a systematic exploration of the energy landscape of phototrophic sulfur oxidation
    Applied and Environmental Microbiology, 2016
    Co-Authors: Thomas E. Hanson, Amalie T Levy, Kelvin H Lee
    Abstract:

    Microbial sulfur metabolism, particularly the formation and consumption of insoluble elemental sulfur (S(0)), is an important biogeochemical engine that has been harnessed for applications ranging from bioleaching and biomining to remediation of waste streams. Chlorobaculum tepidum , a low-light adapted photoautolithotrophic sulfur oxidizing bacterium, oxidizes multiple sulfur species and displays a preference for more reduced electron donors: sulfide > S(0) > thiosulfate. To understand this preference in the context of light energy availability, an ‘energy landscape’ of phototrophic sulfur oxidation was constructed by varying electron donor identity, light flux, and culture duration. Biomass and cellular parameters of Cba. tepidum cultures grown across this landscape were analyzed. From these data, a correction factor for colorimetric protein assays was developed, enabling more accurate biomass measurements for Cba. tepidum as well as other organisms. Cba. tepidum ’s bulk amino acid composition correlated with energy landscape parameters, including a tendency toward less energetically expensive amino acids under reduced light flux. This correlation, paired with an observation of increased cell size and storage carbon production under electron-rich growth conditions, suggests that Cba. tepidum has evolved to cope with changing energy availability by tuning its proteome for energetic efficiency and storing compounds for leaner times. IMPORTANCE: How microbes cope with and adapt to varying energy availability is an important factor in understanding microbial ecology and in designing efficient biotechnological processes. We explored the response of a model phototrophic organism, Chlorobaculum tepidum , across a factorial experimental design that enabled simultaneous variation and analysis of multiple growth conditions, what we term the ‘energy landscape’. Cba. tepidum biomass composition shifted toward less energetically expensive amino acids at low light. This observation provides experimental evidence for evolved efficiencies in microbial proteomes and emphasizes the role that energy flux may play in the adaptive responses of organisms. From a practical standpoint, our data suggest that bulk biomass amino acid composition could provide a simple proxy to monitor and identify energy stress in microbial systems.

Robert E. Blankenship - One of the best experts on this subject based on the ideXlab platform.

  • on excitation energy transfer within the baseplate bchl a csma complex of chloroflexus aurantiacus
    Journal of Physical Chemistry B, 2019
    Co-Authors: Mahboobe Jassas, Robert E. Blankenship, Ryszard Jankowiak, Carrie Goodson, Adam Kell
    Abstract:

    Recently, a hybrid approach combining solid-state NMR spectroscopy and cryo-electron microscopy showed that the baseplate in green sulfur bacterium Chlorobaculum tepidum is a 2D lattice of BChl a–C...

  • ultrafast spectroscopic investigation of energy transfer in site directed mutants of the fenna matthews olson fmo antenna complex from Chlorobaculum tepidum
    Journal of Physical Chemistry B, 2017
    Co-Authors: Nikki Cecil M Magdaong, Rafael G Saer, Dariusz M Niedzwiedzki, Robert E. Blankenship
    Abstract:

    Ultrafast transient absorption (TA) and time-resolved fluorescence (TRF) spectroscopic studies were performed on several mutants of the bacteriochlorophyll (BChl) a-containing Fenna–Matthews–Olson (FMO) complex from the green sulfur bacterium Chlorobaculum tepidum. These mutants were generated to perturb a particular BChl a site and determine its effects on the optical spectroscopic properties of the pigment–protein complex. Measurements conducted at 77 K under both oxidizing and reducing conditions revealed changes in the dynamics of the various spectral components as compared to the data set from wild-type FMO. TRF results show that under reducing conditions all FMO samples decay with a similar lifetime in the ∼2 ns range. The oxidized samples revealed varying fluorescence lifetimes of the terminal BChl a emitter, considerably shorter than those recorded for the reduced samples, indicating that the quenching mechanism in wild-type FMO is still present in the mutants. Global fitting of TA data yielded si...

  • probing the excitonic landscape of the Chlorobaculum tepidum fenna matthews olson fmo complex a mutagenesis approach
    Biochimica et Biophysica Acta, 2017
    Co-Authors: Rafael G Saer, Nikki Cecil M Magdaong, Valentyn Stadnytskyi, Carrie Goodson, Sergei Savikhin, Robert E. Blankenship
    Abstract:

    In this paper we report the steady-state optical properties of a series of site-directed mutants in the Fenna-Matthews-Olson (FMO) complex of Chlorobaculum tepidum, a photosynthetic green sulfur bacterium. The FMO antenna complex has historically been used as a model system for energy transfer due to the water-soluble nature of the protein, its stability at room temperature, as well as the availability of high-resolution structural data. Eight FMO mutants were constructed with changes in the environment of each of the bacteriochlorophyll a pigments found within each monomer of the homotrimeric FMO complex. Our results reveal multiple changes in low temperature absorption, as well as room temperature CD in each mutant compared to the wild-type FMO complex. These datasets were subsequently used to model the site energies of each pigment in the FMO complex by employing three different Hamiltonians from the literature. This enabled a basic approximation of the site energy shifts imparted on each pigment by the changed amino acid residue. These simulations suggest that, while the three Hamiltonians used in this work provide good fits to the wild-type FMO absorption spectrum, further efforts are required to obtain good fits to the mutant minus wild-type absorption difference spectra. This demonstrates that the use of FMO mutants can be a valuable tool to refine and iterate the current models of energy transfer in this system.

  • Ultrafast Spectroscopic Investigation of Energy Transfer in Site-Directed Mutants of the Fenna–Matthews–Olson (FMO) Antenna Complex from Chlorobaculum tepidum
    2017
    Co-Authors: Nikki Cecil M Magdaong, Rafael G Saer, Dariusz M Niedzwiedzki, Robert E. Blankenship
    Abstract:

    Ultrafast transient absorption (TA) and time-resolved fluorescence (TRF) spectroscopic studies were performed on several mutants of the bacteriochlorophyll (BChl) a-containing Fenna–Matthews–Olson (FMO) complex from the green sulfur bacterium Chlorobaculum tepidum. These mutants were generated to perturb a particular BChl a site and determine its effects on the optical spectroscopic properties of the pigment–protein complex. Measurements conducted at 77 K under both oxidizing and reducing conditions revealed changes in the dynamics of the various spectral components as compared to the data set from wild-type FMO. TRF results show that under reducing conditions all FMO samples decay with a similar lifetime in the ∼2 ns range. The oxidized samples revealed varying fluorescence lifetimes of the terminal BChl a emitter, considerably shorter than those recorded for the reduced samples, indicating that the quenching mechanism in wild-type FMO is still present in the mutants. Global fitting of TA data yielded similar overall results, and in addition, the lifetimes of early decaying components were determined. Target analyses of TA data for select FMO samples generated kinetic models that better simulate the TA data. A comparison of the lifetime of excitonic components for all samples reveals that the mutations affect mainly the early kinetic components, but not that of the lowest energy exciton, which reflects the flexibility of energy transfer in FMO

  • ultrafast spectroscopic investigation of energy transfer in site directed mutants of the fenna matthews olson fmo antenna complex from Chlorobaculum tepidum b
    The Journal of Physical Chemistry, 2017
    Co-Authors: Nikki Cecil M Magdaong, Rafael G Saer, Dariusz M Niedzwiedzki, Robert E. Blankenship
    Abstract:

    Ultrafast transient absorption (TA) and time-resolved fluorescence (TRF) spectroscopic studies were performed on several mutants of the bacteriochlorophyll (BChl) a-containing Fenna–Matthews–Olson (FMO) complex from the green sulfur bacterium Chlorobaculum tepidum. These mutants were generated to perturb a particular BChl a site and determine its effects on the optical spectroscopic properties of the pigment–protein complex. Measurements conducted at 77 K under both oxidizing and reducing conditions revealed changes in the dynamics of the various spectral components as compared to the data set from wild-type FMO. TRF results show that under reducing conditions all FMO samples decay with a similar lifetime in the ∼2 ns range. The oxidized samples revealed varying fluorescence lifetimes of the terminal BChl a emitter, considerably shorter than those recorded for the reduced samples, indicating that the quenching mechanism in wild-type FMO is still present in the mutants. Global fitting of TA data yielded similar overall results, and in addition, the lifetimes of early decaying components were determined. Target analyses of TA data for select FMO samples generated kinetic models that better simulate the TA data. A comparison of the lifetime of excitonic components for all samples reveals that the mutations affect mainly the early kinetic components, but not that of the lowest energy exciton, which reflects the flexibility of energy transfer in FMO.

Donatas Zigmantas - One of the best experts on this subject based on the ideXlab platform.

  • Two-Dimensional Electronic Spectroscopy Reveals Ultrafast Energy Diffusion in Chlorosomes
    2016
    Co-Authors: Jakub Dostál, Tomáš Mančal, Ramu-nas Augulis, František Vácha, Jakub Pšenčík, Donatas Zigmantas
    Abstract:

    Chlorosomes are light-harvesting antennae that enable exceptionally efficient light energy capture and excitation transfer. They are found in certain photosynthetic bacteria, some of which live in extremely low-light environments. In this work, chlorosomes from the green sulfur bacterium Chlorobaculum tepidum were studied by coherent electronic two-dimensional (2D) spectroscopy. Previously uncharacterized ultrafast energy transfer dynamics were followed, appearing as evolution of the 2D spectral line-shape during the first 200 fs after excitation. Observed initial energy flow through the chlorosome is well explained by effective exciton diffusion on a sub-100 fs time scale, which assures efficiency and robustness of the process. The ultrafast incoherent diffusion-like behavior of the excitons points to a disordered energy landscape in the chlorosome, which leads to a rapid loss of excitonic coherences between its structural subunits. This disorder prevents observation of excitonic coherences in the experimental data and implies that the chlorosome as a whole does not function as a coherent light-harvester

  • 2D Electronic Spectroscopy Reveals Excitonic Structure in the Baseplate of a Chlorosome
    2015
    Co-Authors: Jakub Dostál, František Vácha, Jakub Pšenčík, Donatas Zigmantas
    Abstract:

    In green photosynthetic bacteria, the chlorosome baseplate mediates excitation energy transfer from the interior of the light-harvesting chlorosome toward the reaction centers. However, the electronic states of the baseplate remain unexplored, hindering the mechanistic understanding of the baseplate as an excitation energy collector and mediator. Here we use two-dimensional spectroscopy to study the excited state structure and internal energy relaxation in the baseplate of green sulfur bacterium Chlorobaculum tepidum. We resolved an exciton system with four energy states, indicating that the organization of the pigments in the baseplate is more complex than was thought before and constitutes at least four bacteriochlorophyll molecules in a close contact. Based on the finding that the energy of the baseplate states is in the same range as in the adjacent Fenna–Matthews–Olson complex, we propose a “lateral” energy transfer pathway, where excitation energy can flow through the photosynthetic unit via all the states of individual complexes

  • 2D Electronic Spectroscopy Reveals Excitonic Structure in the Baseplate of a Chlorosome.
    Journal of Physical Chemistry Letters, 2014
    Co-Authors: Jakub Dostál, Jakub Pšenčík, Frantisek Vacha, Donatas Zigmantas
    Abstract:

    In green photosynthetic bacteria, the chlorosome baseplate mediates excitation energy transfer from the interior of the light-harvesting chlorosome toward the reaction centers. However, the electronic states of the baseplate remain unexplored, hindering the mechanistic understanding of the baseplate as an excitation energy collector and mediator. Here we use two-dimensional spectroscopy to study the excited state structure and internal energy relaxation in the baseplate of green sulfur bacterium Chlorobaculum tepidum. We resolved an exciton system with four energy states, indicating that the organization of the pigments in the baseplate is more complex than was thought before and constitutes at least four bacteriochlorophyll molecules in a close contact. Based on the finding that the energy of the baseplate states is in the same range as in the adjacent Fenna-Matthews-Olson complex, we propose a "lateral" energy transfer pathway, where excitation energy can flow through the photosynthetic unit via all the states of individual complexes.

  • Fast Exciton Dynamics and Coherent Oscillations Revealed by Coherent 2D Spectroscopy in Chlorosomes
    'EDP Sciences', 2013
    Co-Authors: J. Dostál, Jakub Pšenčík, Ramu-nas Augulis, Tomáš Mančal, F. Vácha, Donatas Zigmantas
    Abstract:

    In this study ultrafast energy transfer dynamics in chlorosomes from sulphur bacterium Chlorobaculum tepidum were explored by means of coherent electronic two-dimensional spectroscopy. Observed sub-100 fs dynamics were attributed to incoherent downhill excitation diffusion between disordered domains within chlorosomes. At the same time vibrational coherent oscillations were investigated on the longer timescales

  • Fast Exciton Dynamics and Coherent Oscillations Revealed by Coherent 2D Spectroscopy in Chlorosomes
    2013
    Co-Authors: Jakub Dostál, Jakub Pšenčík, Ramu-nas Augulis, Tomáš Mančal, J. Dostál, F. Vácha, Donatas Zigmantas
    Abstract:

    Republic Abstract. In this study ultrafast energy transfer dynamics in chlorosomes from sulphur bacterium Chlorobaculum tepidum were explored by means of coherent electronic two-dimensional spectroscopy. Observed sub-100 fs dynamics were attributed to incoherent downhill excitation diffusion between disordered domains within chlorosomes. At the same time vibrational coherent oscillations were investigated on the longer timescales.

Ryszard Jankowiak - One of the best experts on this subject based on the ideXlab platform.

  • on excitation energy transfer within the baseplate bchl a csma complex of chloroflexus aurantiacus
    Journal of Physical Chemistry B, 2019
    Co-Authors: Mahboobe Jassas, Robert E. Blankenship, Ryszard Jankowiak, Carrie Goodson, Adam Kell
    Abstract:

    Recently, a hybrid approach combining solid-state NMR spectroscopy and cryo-electron microscopy showed that the baseplate in green sulfur bacterium Chlorobaculum tepidum is a 2D lattice of BChl a–C...

  • Impact of Single-Point Mutations on the Excitonic Structure and Dynamics in a Fenna–Matthews–Olson Complex
    2018
    Co-Authors: Anton Khmelnitskiy, Tonu Reinot, Ryszard Jankowiak
    Abstract:

    Hole burning (HB) spectroscopy and modeling studies reveal significant changes in the excitonic structure and dynamics in several mutants of the FMO trimer from the Chlorobaculum tepidum. The excited-state decay times (T1) of the high-energy excitons are significantly modified when mutation occurs near bacteriochlorophyll (BChl) 1 (V152N mutant) or BChl 6 (W184F). Longer (averaged) T1 times of highest-energy excitons in V152N and W184F mutants suggest that site energies of BChls 1 and 6, believed to play an important role in receiving excitation from the baseplate BChls, likely play a critical role to ensure the femtosecond (fs) energy relaxation observed in wild-type FMO. HB spectroscopy reveals preferentially slower T1 times (about 1 ps on average) because fs times prohibit HB due to an extremely low HB quantum yield. Uncorrelated (incoherent) excitation energy transfer times between monomers, the composition of exciton states, and average, frequency-dependent, excited-state decay times (T1) are discussed

  • effect of spectral density shapes on the excitonic structure and dynamics of the fenna matthews olson trimer from Chlorobaculum tepidum
    Journal of Physical Chemistry A, 2016
    Co-Authors: Adam Kell, Robert E. Blankenship, Ryszard Jankowiak
    Abstract:

    The Fenna–Matthews–Olson (FMO) trimer (composed of identical subunits) from the green sulfur bacterium Chlorobaculum tepidum is an important protein model system to study exciton dynamics and excitation energy transfer (EET) in photosynthetic complexes. In addition, FMO is a popular model for excitonic calculations, with many theoretical parameter sets reported describing different linear and nonlinear optical spectra. Due to fast exciton relaxation within each subunit, intermonomer EET results predominantly from the lowest energy exciton states (contributed to by BChl a 3 and 4). Using experimentally determined shapes for the spectral densities, simulated optical spectra are obtained for the entire FMO trimer. Simultaneous fits of low-temperature absorption, fluorescence, and hole-burned spectra place constraints on the determined pigment site energies, providing a new Hamiltonian that should be further tested to improve modeling of 2D electronic spectroscopy data and our understanding of coherent and di...

  • Effect of Spectral Density Shapes on the Excitonic Structure and Dynamics of the Fenna–Matthews–Olson Trimer from Chlorobaculum tepidum
    2016
    Co-Authors: Adam Kell, Robert E. Blankenship, Ryszard Jankowiak
    Abstract:

    The Fenna–Matthews–Olson (FMO) trimer (composed of identical subunits) from the green sulfur bacterium Chlorobaculum tepidum is an important protein model system to study exciton dynamics and excitation energy transfer (EET) in photosynthetic complexes. In addition, FMO is a popular model for excitonic calculations, with many theoretical parameter sets reported describing different linear and nonlinear optical spectra. Due to fast exciton relaxation within each subunit, intermonomer EET results predominantly from the lowest energy exciton states (contributed to by BChl a 3 and 4). Using experimentally determined shapes for the spectral densities, simulated optical spectra are obtained for the entire FMO trimer. Simultaneous fits of low-temperature absorption, fluorescence, and hole-burned spectra place constraints on the determined pigment site energies, providing a new Hamiltonian that should be further tested to improve modeling of 2D electronic spectroscopy data and our understanding of coherent and dissipation effects in this important protein complex

  • alternative excitonic structure in the baseplate bchl a csma complex of the chlorosome from Chlorobaculum tepidum
    Journal of Physical Chemistry Letters, 2015
    Co-Authors: Adam Kell, Joseph Kuohsiang Tang, Jinhai Chen, Mahboobe Jassas, Ryszard Jankowiak
    Abstract:

    In the photosynthetic green sulfur bacterium Chlorobaculum tepidum, the baseplate mediates excitation energy transfer from the light-harvesting chlorosome to the Fenna-Matthews-Olson (FMO) complex and subsequently toward the reaction center (RC). Literature data suggest that the baseplate is a 2D lattice of BChl a-CsmA dimers. However, recently, it has been proposed, using 2D electronic spectroscopy (2DES) at 77 K, that at least four excitonically coupled BChl a are in close contact within the baseplate structure [ Dostal , J. ; et al., J. Phys. Chem. Lett. 2014 , 5 , 1743 ]. This finding is tested via hole burning (HB) spectroscopy (5 K). Our results indicate that the four excitonic states identified by 2DES likely correspond to contamination of the baseplate with the FMO antenna and possibly the RC. In contrast, HB reveals a different excitonic structure of the baseplate chromophores, where excitation is transferred to a localized trap state near 818 nm via exciton hopping, which leads to emission near 826 nm.

Jiro Harada - One of the best experts on this subject based on the ideXlab platform.

  • in vitro hydrolysis of zinc chlorophyllide a homologues by a bcic enzyme
    Biochemistry, 2020
    Co-Authors: Mitsuaki Hirose, Jiro Harada, Hitoshi Tamiaki
    Abstract:

    Chlorosomes in green photosynthetic bacteria are the largest and most efficient light-harvesting antenna systems of all phototrophs. The core part of chlorosomes consists of bacteriochlorophyll c, d, or e molecules. In their biosynthetic pathway, a BciC enzyme catalyzes the removal of the C132-methoxycarbonyl group of chlorophyllide a. In this study, the in vitro enzymatic reactions of chlorophyllide a analogues, C132-methylene- and ethylene-inserted zinc complexes, were examined using a BciC protein from Chlorobaculum tepidum. As the products, their hydrolyzed free carboxylic acids were observed without the corresponding demethoxycarbonylated compounds. The results showed that the in vivo demethoxycarbonylation of chlorophyllide a by an action of the BciC enzyme would occur via two steps: (1) an enzymatic hydrolysis of a methyl ester at the C132-position, followed by (2) a spontaneous (nonenzymatic) decarboxylation in the resulting carboxylic acid.

  • anaerobic energy dissipation by glycosylated carotenoids in the green sulfur bacterium Chlorobaculum tepidum
    Journal of Photochemistry and Photobiology A-chemistry, 2020
    Co-Authors: Chihiro Azai, Jiro Harada, Shinji Masuda, Shogo Fujimoto, Daisuke Kosumi
    Abstract:

    Abstract Carotenoids are linear polyenes and universal pigment molecules that support natural photosynthesis by light harvesting and photoprotection. Some carotenoids are glycosylated at the end of their polyene backbone, which does not clearly affect their photochemical and optical properties. In green sulfur bacteria (GSBs), which are obligate photosynthetic anaerobes, carotenoid glycosides are specifically bound to the photosynthetic reaction center (RC) complex. The other non-glycosylated carotenoids with the same polyene backbone are located in the chlorosome, which is an extra-large light-harvesting organelle. The current study isolated a mutant strain, ΔcruC, that lacks the gene responsible for carotenoid glycosylation in the model GSB species Chlorobaculum tepidum. We examined the effects of the mutation on photosynthetic growth and energy transfer reactions. The ΔcruC mutant cells grew significantly slower than the wild-type (WT) cells under high light conditions. Energy transfer reactions were delayed between bacteriochlorophyll (BChl) a of the RC complex, despite no obvious effect observed on the organization of photosynthetic apparatuses. Kinetic analyses revealed that almost half of the excitation energy of BChl a was constitutively quenched in the WT RC complex, even under a strictly anaerobic environment. The ΔcruC mutant strain phenotype clearly indicates that glycosylated carotenoids serve as energy dissipating, not light harvesting, pigments in C. tepidum. The current understanding of natural photosynthesis is that any energy dissipation mechanisms should be to avoid generation of reactive oxygen species, which are sensitized by the triplet-excited state of chlorophylls. However, these results indicate that carotenoid glycosides found in GSB may also serve a previously unidentified function for anaerobic energy dissipation.

  • Specific gene bciD for C7-methyl oxidation in bacteriochlorophyll e biosynthesis of brown-coloured green sulfur bacteria. PLoS One 2013
    2016
    Co-Authors: Jiro Harada, Yusuke Tsukatani, Tadashi Mizoguchi, Masato Noguchi, Ayumi Tanaka, Hitoshi Tamiaki
    Abstract:

    The gene named bciD, which encodes the enzyme involved in C7-formylation in bacteriochlorophyll e biosynthesis, was found and investigated by insertional inactivation in the brown-colored green sulfur bacterium Chlorobaculum limnaeum (previously called Chlorobium phaeobacteroides). The bciD mutant cells were green in color, and accumulated bacteriochlorophyll c homologs bearing the 7-methyl group, compared to C7-formylated BChl e homologs in the wild type. BChl-c homolog compositions in the mutant were further different from those in Chlorobaculum tepidum which originally produced BChl c: (31S)-8-isobutyl-12-ethyl-BChl c was unusually predominant

  • stereochemical conversion of c3 vinyl group to 1 hydroxyethyl group in bacteriochlorophyll c by the hydratases bchf and bchv adaptation of green sulfur bacteria to limited light environments
    Molecular Microbiology, 2015
    Co-Authors: Jiro Harada, Yusuke Tsukatani, Tadashi Mizoguchi, Misato Teramura, Ken Yamamoto, Hitoshi Tamiaki
    Abstract:

    Photosynthetic green sulfur bacteria inhabit anaerobic environments with very low-light conditions. To adapt to such environments, these bacteria have evolved efficient light-harvesting antenna complexes called as chlorosomes, which comprise self-aggregated bacteriochlorophyll c in the model green sulfur, bacterium Chlorobaculum tepidum. The pigment possess a hydroxy group at the C3(1) position that produces a chiral center with R- or S-stereochemistry and the C3(1) -hydroxy group serves as a connecting moiety for the self-aggregation. Chlorobaculum tepidum carries the two possible homologous genes for C3-vinyl hydratase, bchF and bchV. In the present study, we constructed deletion mutants of each of these genes. Pigment analyses of the bchF-inactivated mutant, which still has BchV as a sole hydratase, showed higher ratios of S-epimeric bacteriochlorophyll c than the wild-type strain. The heightened prevalence of S-stereoisomers in the mutant was more remarkable at lower light intensities and caused a red shift of the chlorosomal Qy absorption band leading to advantages for light-energy transfer. In contrast, the bchV-mutant possessing only BchF showed a significant decrease of the S-epimers and accumulations of C3-vinyl BChl c species. As trans- criptional level of bchV was upregulated at lower light intensity, the Chlorobaculum tepidum adapted to low-light environments by control of the bchV transcription.

  • In Vitro Enzymatic Activities of Bacteriochlorophyll a Synthase Derived from the Green Sulfur Photosynthetic Bacterium Chlorobaculum tepidum
    Biochemistry, 2015
    Co-Authors: Yoshitaka Saga, Jiro Harada, Keiya Hirota, Hitoshi Tamiaki
    Abstract:

    The activity of an enzyme encoded by the CT1610 gene in the green sulfur photosynthetic bacterium Chlorobaculum tepidum, which was annotated as bacteriochlorophyll (BChl) a synthase, BchG (denoted as tepBchG), was examined in vitro using the lysates of Escherichia coli containing the heterologously expressed enzyme. BChl a possessing a geranylgeranyl group at the 17-propionate residue (BChl aGG) was produced from bacteriochlorophyllide (BChlide) a and geranylgeranyl pyrophosphate in the presence of tepBchG. Surprisingly, tepBchG catalyzed the formation of BChl a bearing a farnesyl group (BChl aF) as in the enzymatic production of BChl aGG, indicating loose recognition of isoprenoid pyrophosphates in tepBchG. In contrast to such loose recognition of isoprenoid substrates, BChlide c and chlorophyllide a gave no esterifying product upon being incubated with geranylgeranyl or farnesyl pyrophosphate in the presence of tepBchG. These results confirm that tepBchG undoubtedly acts as the BChl a synthase in Cba. t...