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1.
Science ; 368(6498): 1490-1495, 2020 06 26.
Artigo em Inglês | MEDLINE | ID: mdl-32587021

RESUMO

Photosynthesis achieves near unity light-harvesting quantum efficiency yet it remains unknown whether there exists a fundamental organizing principle giving rise to robust light harvesting in the presence of dynamic light conditions and noisy physiological environments. Here, we present a noise-canceling network model that relates noisy physiological conditions, power conversion efficiency, and the resulting absorption spectra of photosynthetic organisms. Using light conditions in full solar exposure, light filtered by oxygenic phototrophs, and light filtered under seawater, we derived optimal absorption characteristics for efficient solar power conversion. We show how light-harvesting antennae can be tuned to maximize power conversion efficiency by minimizing excitation noise, thus providing a unified theoretical basis for the observed wavelength dependence of absorption in green plants, purple bacteria, and green sulfur bacteria.


Assuntos
Complexos de Proteínas Captadores de Luz/fisiologia , Fotossíntese , Plantas/metabolismo , Proteobactérias/metabolismo , Adsorção , Chlorobi , Transferência de Energia , Luz , Oxigênio , Energia Solar
2.
Chemosphere ; 256: 127101, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32450355

RESUMO

Previous studies of the dynamics of sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) have focused on deep stratified lakes. The objective of this study is to present an in-depth investigation of the structure and dynamics of sulfur bacteria (including SRB and SOB) in the water column of shallow freshwater lakes. A cyanobacterial bloom biomass (CBB)-amended mesocosm experiment was conducted in this study, in which water was taken from a shallow eutrophic lake with sulfate levels near 40 mg L-1. Illumina sequencing was used to investigate SRB and SOB species involved in CBB decomposition and the effects of the increases in sulfate input on the water column microbial community structure. The accumulation of dissolved sulfide (∑H2S) produced by SRB during CBB decomposition stimulated the growth of SOB, and ∑H2S was then oxidized back to sulfate by SOB in the water column. Chlorobaculum sequences (the main SOB species in the study) were significantly influenced by increases in sulfate input, with relative abundance increasing approximately four-fold in treatments amended with 40 mg L-1 sulfate (referred to as 40S) when compared to the treatment without additional sulfate addition (referred to as CU). Additionally, an increase in SOB number was observed from day 26-37, concurrent with the decrease in SRB number, indicating the succession of sulfur bacteria. These findings suggest that biological sulfur oxidation and succession of sulfur bacteria occur in the water column during CBB decomposition in shallow freshwater ecosystems, and the increases in sulfate input stimulate microbial sulfur oxidation.


Assuntos
Cianobactérias/crescimento & desenvolvimento , Lagos/microbiologia , Biomassa , Chlorobi , Ecossistema , Oxirredução , Sulfatos , Sulfetos , Enxofre/química
3.
J Phys Chem Lett ; 11(5): 1636-1643, 2020 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-32013435

RESUMO

High efficiency of light harvesting in photosynthetic pigment-protein complexes is governed by evolutionary-perfected protein-assisted tuning of individual pigment properties and interpigment interactions. Due to the large number of spectrally overlapping pigments in a typical photosynthetic complex, experimental methods often fail to unambiguously identify individual chromophore properties. Here, we report a first-principles-based modeling protocol capable of predicting properties of pigments in protein environment to a high precision. The technique was applied to successfully uncover electronic properties of the Fenna-Matthews-Olson (FMO) pigment-protein complex. Each of the three subunits of the FMO complex contains eight strongly coupled bacteriochlorophyll a (BChl a) pigments. The excitonic structure of FMO can be described by an electronic Hamiltonian containing excitation (site) energies of BChl a pigments and electronic couplings between them. Several such Hamiltonians have been developed in the past based on the information from various spectroscopic measurements of FMO; however, fine details of the excitonic structure and energy transfer in FMO, especially assignments of short-lived high-energy sites, remain elusive. Utilizing polarizable embedding quantum mechanics/molecular mechanics with the effective fragment potentials, we computed the electronic Hamiltonian of FMO that is in general agreement with previously reported empirical Hamiltonians and quantitatively reproduces experimental absorption and circular dichroism spectra of the FMO protein. The developed computational protocol is sufficiently simple and can be utilized for predictive modeling of other wild-type and mutated photosynthetic pigment-protein complexes.


Assuntos
Proteínas de Bactérias/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Simulação de Dinâmica Molecular , Teoria Quântica , Proteínas de Bactérias/química , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Chlorobi/metabolismo , Dicroísmo Circular , Transferência de Energia , Gases/química , Complexos de Proteínas Captadores de Luz/química , Fotossíntese
4.
Int J Syst Evol Microbiol ; 70(1): 358-363, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31622236

RESUMO

Two Gram-stain-negative, moderately halophilic bacteria, designated strains ECH52T and KHM46, were isolated from the sediment of a grey saltern located in Sinui island at Shinan, Korea. The isolates were aerobic, non-motile, short rods and grew at 15-45 °C (optimum, 37 °C), at pH 6.0-10.0 (optimum, pH 8.0) and with 3-25 % (w/v) NaCl (optimum, 10 % NaCl). Phylogenetic analyses based on 16S rRNA gene sequences indicated that strains ECH52T and KHM46 belonged to the genus Aliifodinibius in the family Balneolaceae with sequence similarities of 94.3-98.6 % and showed the highest sequence similarity to Aliifodinibius halophilus 2W32T (98.6 %), A. sediminis YIM J21T (94.7%), A. salicampi KHM44T (94.6 %) and A. roseus YIM D15T (94.3 %). The DNA G+C content of the genomic DNA of strain ECH52T was 40.8 mol%. The predominant isoprenoid quinone was menaquinone-7 (MK-7) and the major cellular fatty acids were iso-C17 : 1ω9c, iso-C15 : 0, and C16 : 1ω7c and/or iso-C15 : 0 2-OH. The major polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, two unidentified glycolipids and four unidentified lipids. Based on the phylogenetic, phenotypic and chemotaxonomic data, strains ECH52T and KHM46 are considered to represent a novel species of the genus Aliifodinibius , for which the name Aliifodinibius saliphilus sp. nov. is proposed. The type strain is ECH52T (=KACC 19126T=NBRC 112664T).


Assuntos
Bacteroides/classificação , Chlorobi/classificação , Filogenia , Tanques/microbiologia , Salinidade , Técnicas de Tipagem Bacteriana , Bacteroides/isolamento & purificação , Composição de Bases , Chlorobi/isolamento & purificação , DNA Bacteriano/genética , Ácidos Graxos/química , Fosfolipídeos/química , RNA Ribossômico 16S/genética , República da Coreia , Análise de Sequência de DNA , Vitamina K 2/análogos & derivados , Vitamina K 2/química , Microbiologia da Água
5.
J Chem Theory Comput ; 16(2): 1175-1187, 2020 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-31841349

RESUMO

In order to study Förster resonance energy transfer (FRET), the fragment molecular orbital (FMO) method is extended to compute electronic couplings between local excitations via the excited state transition density model, enabling efficient calculations of nonlocal excitations in a large molecular system and overcoming the previous limitation of being able to compute only local excitations. The results of these simple but accurate models are validated against full quantum calculations without fragmentation. The developed method is applied to a very important photosynthetic pigment-protein complex, the Fenna-Matthews-Olson complex (FMOc), that is responsible for the energy transfer from a chlorosome to the reaction center in the green sulfur bacteria. Absorption and circular dichroism spectra of FMOc are simulated, and the role of the molecular environment on the excitations is revealed.


Assuntos
Proteínas de Bactérias/química , Complexos de Proteínas Captadores de Luz/química , Modelos Moleculares , Teoria Quântica , Proteínas de Bactérias/metabolismo , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Chlorobi/metabolismo , Transferência Ressonante de Energia de Fluorescência , Complexos de Proteínas Captadores de Luz/metabolismo
6.
Biochemistry (Mosc) ; 84(11): 1403-1410, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31760926

RESUMO

Genomes of photoautotrophic organisms containing type I photosynthetic reaction center were searched for the rnf genes encoding Na+-translocating ferredoxin:NAD+ oxidoreductase (RNF). These genes were absent in heliobacteria, cyanobacteria, algae, and plants; however, genomes of many green sulfur bacteria (especially marine ones) were found to contain the full rnf operon. Analysis of RNA isolated from the marine green sulfur bacterium Chlorobium phaeovibrioides revealed a high level of rnf expression. It was found that the activity of Na+-dependent flavodoxin:NAD+ oxidoreductase detected in the membrane fraction of Chl. phaeovibrioides was absent in the membrane fraction of the freshwater green sulfur bacterium Chlorobaculum limnaeum, which is closely related to Chl. phaeovibrioides but whose genome lacks the rnf genes. Illumination of the membrane fraction of Chl. phaeovibrioides but not of Cba. limnaeum resulted in the light-induced NAD+ reduction. Based on the obtained data, we concluded that in some green sulfur bacteria, RNF may be involved in the NADH formation that should increase the efficiency of light energy conservation in these microorganisms and can serve as the first example of the use of Na+ energetics in photosynthetic electron transport chains.


Assuntos
Proteínas de Bactérias/metabolismo , Chlorobi/metabolismo , Oxirredutases/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Transporte de Elétrons , Luz , NAD/química , NAD/metabolismo , Oxirredutases/química , Oxirredutases/genética , Fotossíntese , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação
7.
Water Res ; 165: 115004, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31470280

RESUMO

A combined heterotrophic-sulfur-autotrophic system (CHSAS) was established to simultaneously reduce perchlorate and nitrate in water. In this system, the OH- produced by the acetate heterotrophic part (H-part) could be neutralized with the H+ produced by the sulfur autotrophic part (S-part); thus, the pH of the final effluent could keep neutral. In addition, the S-part could further reduce the pollutants and residual carbon from the H-part to achieve a high performance. For 19.62 ±â€¯0.30 mg/L ClO4- and 21.56 ±â€¯0.83 mg/L NO3--N in the influent, the operating parameters were optimal at a hydraulic retention time (HRT) of 1.0 h and an acetate concentration of 70 mg/L. The removal efficiency of ClO4- and NO3- reached 95.43% and 99.23%, without secondary pollution caused by residual organic carbon. It was also revealed that sulfur (S0) disproportionation can be inhibited by shortening the HRT and reducing the acetate dosage. The dominant heterotrophic and autotrophic bacteria were Thauera and Ferritrophicum, respectively, while Chlorobaculum was related to S0 disproportionation.


Assuntos
Chlorobi , Microbiota , Processos Autotróficos , Reatores Biológicos , Desnitrificação , Concentração de Íons de Hidrogênio , Nitratos , Percloratos , Enxofre
8.
Photosynth Res ; 142(2): 127-136, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31302833

RESUMO

Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides (cp-Fld). The expression of the cp-Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp-Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known flavodoxins. However, unlike all other flavodoxins, cp-Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone-semiquinone and semiquinone-quinol couples (- 110 and - 530 mV, respectively). cp-Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use flavodoxin as an alternative electron carrier to cope with iron deficiency.


Assuntos
Chlorobi/metabolismo , Flavina-Adenina Dinucleotídeo/análogos & derivados , Flavodoxina/metabolismo , Ar , Chlorobi/genética , Espectroscopia de Ressonância de Spin Eletrônica , Elétrons , Escherichia coli/metabolismo , Flavina-Adenina Dinucleotídeo/metabolismo , Oxirredução , Piruvato Sintase/metabolismo
9.
Arch Microbiol ; 201(10): 1399-1404, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31338544

RESUMO

A Gram-negative, anaerobic photoautotroph, nonmotile, oval bacterium possessing gas vesicles and having no prosthecae, designated as V1, was isolated from the South China Sea coastal zone. It had chlorosomes as photosynthetic structures, and bacteriochlorophyll c as the major photosynthetic pigment. The strain was found to grow at 20-35 °C, pH 6.3-8.0 (optimum, pH 7.1) and with 0.7-5.8% (w/v) NaCl (optimum, 1-1.8%). In the presence of sulfide and bicarbonate, acetate, and fructose promoted growth. The DNA G+C content was 47 mol%. While the new isolate belonged to the Chlorobiaceae genus Prosthecochloris, it exhibited low similarity of the 16S rRNA gene sequences (96.21-96.78%) to other members of this genus. Comparison of the genome nucleotide sequences of strain V1 revealed that the new isolate was remote from the Chlorobiaceae type strains both in dDDH (16.8-18.9%) and in ANI (75.2-77.8%). We propose to assign the isolate to a new species, Prosthecochloris marina sp. nov., with the type strain V1T ( = VKM-3301T = KCTC 15824T).


Assuntos
Chlorobi/classificação , Filogenia , Organismos Aquáticos , Proteínas de Bactérias/metabolismo , Bacterioclorofilas/metabolismo , Composição de Bases , China , Chlorobi/química , Chlorobi/genética , DNA Bacteriano/genética , Ácidos Graxos/química , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Especificidade da Espécie
10.
Comput Biol Chem ; 80: 206-216, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30981103

RESUMO

All cultivated members of the phylum Chlorobi are classified under the two classes Chlorobia and Ignavibacteria. The recently-reported, uncultivated genome-species of Chlorobi have not suggested any alteration in the dichotomy of the two classes, but have hypothesized the existence of a distinct, aerobic and photoheterotrophic, order/family level lineage within Chlorobia, which otherwise was considered to be a monophyletic group of anaerobic sulfur-photolithoautotrophs. Here we report the discovery of a novel population genome bin (named Chlorobi-445) from the combined metagenomes of three spatially-contiguous but visually-distinct microbial mats growing along the 65-41 °C hydrothermal gradient of a boron-rich microbialite spring located in the Puga geothermal area of Eastern Ladakh, India. 1.3, 8.2 and 3.8% metagenomic reads from the mat communities located at 65 °C, 52 °C and 41 °C sample-sites respectively, were found to map-back to the 2,809,852 bp genome of Chlorobi-445. Phylogenomically, and therefore in terms of potential metabolic attributes, Chlorobi-445 showed close relationship with Ca. Thermochlorobacter aerophilum. Gene content suggested Chlorobi-445 to be an aerobic photoorganoheterotroph. Although this new lineage encodes all the proteins necessary for the biosynthesis of bacteriochlorophylls and the photosynthetic reaction centre, it is potentially devoid of genes concerned with lithotrophic sulfur oxidation and carbon-fixation. Individual Chlorobi phylogenies based on the sequence similarities of 16S rRNA genes, 22 ribosomal proteins, and 56 conserved marker-proteins that are encoded from single-copy genes, unanimously suggested that the class Chlorobia encompasses two major branches/clades. Whereas the Clade-I is a homogeneous cluster of culturable, anaerobic sulfur-/iron-oxidizing photolithoautotrophs, Clade-II harbors (i) Chloroherpeton species, and (ii) uncultivated aerobic photoheterotrophs such as Chlorobi-445, Chlorobium sp. GBChlB &Ca. T. aerophilum, in its two sub-clades. Distribution of bioenergetic attributes over the different branches of Chlorobi, together with the aerobic chemoorganoheterotrophic nature of the deepest-branching genome-species NICIL-2, indicated that the early Chlorobi were aerobic chemoorganoheterotrophs, while anaerobicity, phototrophy, lithotrophy, and autotrophy were all potentially added in the course of evolution.


Assuntos
Chlorobi/classificação , Chlorobi/genética , Metagenoma , Metagenômica/métodos , Filogenia , Proteínas de Bactérias/genética
11.
J R Soc Interface ; 16(151): 20180882, 2019 02 28.
Artigo em Inglês | MEDLINE | ID: mdl-30958204

RESUMO

The Fenna-Matthews-Olson (FMO) light-harvesting antenna protein of green sulfur bacteria is a long-studied pigment-protein complex which funnels energy from the chlorosome to the reaction centre where photochemistry takes place. The structure of the FMO protein from Chlorobaculum tepidum is known as a homotrimeric complex containing eight bacteriochlorophyll a per monomer. Owing to this structure FMO has strong intra-monomer and weak inter-monomer electronic coupling constants. While long-lived (sub-picosecond) coherences within a monomer have been a prevalent topic of study over the past decade, various experimental evidence supports the presence of subsequent inter-monomer energy transfer on a picosecond time scale. The latter has been neglected by most authors in recent years by considering only sub-picosecond time scales or assuming that the inter-monomer coupling between low-energy states is too weak to warrant consideration of the entire trimer. However, Förster theory predicts that energy transfer of the order of picoseconds is possible even for very weak (less than 5 cm-1) electronic coupling between chromophores. This work reviews experimental data (with a focus on emission and hole-burned spectra) and simulations of exciton dynamics which demonstrate inter-monomer energy transfer. It is shown that the lowest energy 825 nm absorbance band cannot be properly described by a single excitonic state. The energy transfer through FMO is modelled by generalized Förster theory using a non-Markovian, reduced density matrix approach to describe the electronic structure. The disorder-averaged inter-monomer transfer time across the 825 nm band is about 27 ps. While only isolated FMO proteins are presented, the presence of inter-monomer energy transfer in the context of the overall photosystem is also briefly discussed.


Assuntos
Proteínas de Bactérias/química , Chlorobi/enzimologia , Complexos de Proteínas Captadores de Luz/química , Modelos Químicos , Proteínas de Bactérias/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo
12.
J Chem Phys ; 150(8): 085102, 2019 Feb 28.
Artigo em Inglês | MEDLINE | ID: mdl-30823745

RESUMO

Energy transport in photosynthetic systems can be tremendously efficient. In particular, we study exciton transport in the Fenna-Mathews-Olson (FMO) complex found in green sulphur bacteria. The exciton dynamics and energy transfer efficiency depend on the interaction of excited chromophores with their environment. Based upon realistic, site-dependent models of the system-bath coupling, we present results that suggest that this interaction may be optimized in the case of FMO. Furthermore we verify two transport pathways and note that one is dominated by coherent dynamics and the other by incoherent energy dissipation. In particular, we note a significant correlation between energy transport efficiency and coherence for exciton transfer from bacteriochlorophyll (BChl) 8 to BChl 4.


Assuntos
Proteínas de Bactérias/metabolismo , Bacterioclorofilas/metabolismo , Transferência de Energia , Modelos Moleculares , Chlorobi/metabolismo , Ligação Proteica
13.
Acta Crystallogr F Struct Biol Commun ; 75(Pt 3): 171-175, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30839291

RESUMO

The Fenna-Matthews-Olson protein from Prosthecochloris aestuarii (PaFMO) has been crystallized in a new form that is amenable to high-resolution X-ray and neutron analysis. The crystals belonged to space group H3, with unit-cell parameters a = b = 83.64, c = 294.78 Å, and diffracted X-rays to ∼1.7 Šresolution at room temperature. Large PaFMO crystals grown to volumes of 0.3-0.5 mm3 diffracted neutrons to 2.2 Šresolution on the MaNDi neutron diffractometer at the Spallation Neutron Source. The resolution of the neutron data will allow direct determination of the positions of H atoms in the structure, which are believed to be fundamentally important in tuning the individual excitation energies of bacteriochlorophylls in this archetypal photosynthetic antenna complex. This is one of the largest unit-cell systems yet studied using neutron diffraction, and will allow the first high-resolution neutron analysis of a photosynthetic antenna complex.


Assuntos
Chlorobi/química , Complexos de Proteínas Captadores de Luz/química , Difração de Nêutrons/métodos , Fotossíntese , Difração de Raios X/métodos , Chlorobi/fisiologia , Conformação Proteica
14.
mBio ; 10(1)2019 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-30647158

RESUMO

J. Hiras, S. V. Sharma, V. Raman, R. A. J. Tinson, et al. (mBio 9:e01603-18, 2018, https://doi.org/10.1128/mBio.01603-18) report on the identification of a novel thiol, N-methyl-bacillithiol (N-Me-BSH), in the green sulfur bacterium Chlorobium tepidum In N-methyl-bacillithiol, the amine of the cysteine is methylated by a novel S-adenosylmethioneine transferase designated N-methyl-bacillithiol synthase A (NmbA). The Hiras et al. study is significant because it is the first report of the presence of N-Me-BSH in anaerobic bacteria.


Assuntos
Cisteína , Compostos de Sulfidrila , Bactérias Anaeróbias , Chlorobi , Cisteína/análogos & derivados , Glucosamina/análogos & derivados
15.
Bioelectrochemistry ; 127: 21-25, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30641310

RESUMO

The syntrophic photosynthesis via direct interspecies electron transfer (DIET) between Geobacter sulfurreducens and Prosthecochloris aestuarii has opened a new paradigm of microbial phototrophy. However, it is still unknown whether this photosynthetic DIET can be mediated by an electrical conductor. Here we report first the photosynthetic DIET in a two-chamber microbial fuel cell (photo-MFC). The photo-MFC worked well and generated a maximum current of 0.6 mA/m2, which validated photosynthetic DIET via the titanium wire. Confocal laser scanning microscopy showed that G. sulfurreducens and P. aestuarii colonized the anode and cathode, respectively. P. aestuarii accepted extracellular electrons from G. sulfurreducens bioanodes under illumination at a current density of 0.6 mA/m2 (normalized to the cathode surface area), which could not be produced in the dark. Such a light-dependent electron uptake from solid electrodes by P. aestuarii was closely related with the presence of CO2, suggesting that P. aestuarii utilized extracellular electrons for photosynthetic CO2 reduction. Electrochemical in situ Fourier transform infrared (FTIR) spectroscopy revealed that certain outer membrane components of the two strains were involved in the DIET process. These results implied photosynthetic DIET can be mediated by electrically conductive materials in natural environments.


Assuntos
Fontes de Energia Bioelétrica/microbiologia , Chlorobi/metabolismo , Geobacter/metabolismo , Técnicas de Cocultura , Condutividade Elétrica , Eletrodos , Transporte de Elétrons , Elétrons , Oxirredução , Fotossíntese
16.
Microbiome ; 7(1): 3, 2019 01 04.
Artigo em Inglês | MEDLINE | ID: mdl-30609942

RESUMO

BACKGROUND: Endolithic microbes in coral skeletons are known to be a nutrient source for the coral host. In addition to aerobic endolithic algae and Cyanobacteria, which are usually described in the various corals and form a green layer beneath coral tissues, the anaerobic photoautotrophic green sulfur bacteria (GSB) Prosthecochloris is dominant in the skeleton of Isopora palifera. However, due to inherent challenges in studying anaerobic microbes in coral skeleton, the reason for its niche preference and function are largely unknown. RESULTS: This study characterized a diverse and dynamic community of endolithic microbes shaped by the availability of light and oxygen. In addition, anaerobic bacteria isolated from the coral skeleton were cultured for the first time to experimentally clarify the role of these GSB. This characterization includes GSB's abundance, genetic and genomic profiles, organelle structure, and specific metabolic functions and activity. Our results explain the advantages endolithic GSB receive from living in coral skeletons, the potential metabolic role of a clade of coral-associated Prosthecochloris (CAP) in the skeleton, and the nitrogen fixation ability of CAP. CONCLUSION: We suggest that the endolithic microbial community in coral skeletons is diverse and dynamic and that light and oxygen are two crucial factors for shaping it. This study is the first to demonstrate the ability of nitrogen uptake by specific coral-associated endolithic bacteria and shed light on the role of endolithic bacteria in coral skeletons.


Assuntos
Antozoários/microbiologia , Chlorobi/classificação , Metagenômica/métodos , Animais , Chlorobi/genética , Chlorobi/isolamento & purificação , DNA Bacteriano/genética , DNA Ribossômico/genética , Filogenia , RNA Ribossômico 16S/genética , Análise de Sequência de DNA
17.
Environ Microbiol ; 21(1): 480-495, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-30452101

RESUMO

Dinitrogen (N2 ) fixing bacteria (diazotrophs) are an important source of new nitrogen in oligotrophic environments and represent stable members of the microbiome in tropical corals, while information on corals from temperate oligotrophic regions is lacking. Therefore, this study provides new insights into the diversity and activity of diazotrophs associated with the temperate coral Oculina patagonica from the Mediterranean Sea by combining metabarcoding sequencing of amplicons of both the 16S rRNA and nifH genes and 15 N2 stable isotope tracer analysis to assess diazotroph-derived nitrogen (DDN) assimilation by the coral. Results show that the diazotrophic community of O. patagonica is dominated by autotrophic bacteria (i.e. Cyanobacteria and Chlorobia). The majority of DDN was assimilated into the tissue and skeletal matrix, and DDN assimilation significantly increased in bleached corals. Thus, diazotrophs may constitute an additional nitrogen source for the coral host, when nutrient exchange with Symbiodinium is disrupted (e.g. bleaching) and external food supply is limited (e.g. oligotrophic summer season). Furthermore, we hypothesize that DDN can facilitate the fast proliferation of endolithic algae, which provide an alternative carbon source for bleached O. patagonica. Overall, O. patagonica could serve as a good model for investigating the importance of diazotrophs in coral recovery from bleaching.


Assuntos
Antozoários/metabolismo , Chlorobi/metabolismo , Cianobactérias/metabolismo , Dinoflagelados/metabolismo , Fixação de Nitrogênio/fisiologia , Animais , Antozoários/microbiologia , Antozoários/parasitologia , Chlorobi/genética , Cianobactérias/genética , Dinoflagelados/genética , Mar Mediterrâneo , Nitrogênio/metabolismo , Oxirredutases/genética , RNA Ribossômico 16S/genética , Estações do Ano
18.
Photosynth Res ; 139(1-3): 163-171, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30182280

RESUMO

Unique light-harvesting antennas in the green sulfur bacterium Chlorobaculum tepidum, called chlorosomes, consist of self-aggregates of bacteriochlorophyll (BChl) c. In the biosynthesis of BChl c, BciC demethoxycarbonylase removes the C132-methoxycarbonyl group to facilitate the self-aggregation of BChl c. We previously reported the in vitro BciC-enzymatic reactions and discussed the function of this enzyme in the biosynthesis of BChl c. This study aims to examine the substrate specificity of BciC in detail using several semi-synthetic (bacterio)chlorophyll derivatives. The results indicate that the substrate specificity of BciC is measurably affected by structural changes on the A/B rings including the bacteriochlorin π-systems. Moreover, BciC showed its activity on a Zn-chelated chlorophyll derivative. On the contrary, BciC recognized structural modifications on the D/E rings, including porphyrin pigments, which resulted in the significant decrease in the enzymatic activity. The utilization of BciC provides mild conditions that may be useful for the in vitro preparation of various chemically (un)stable chlorophyllous pigments.


Assuntos
Chlorobi/metabolismo , Clorofila/metabolismo , Proteínas de Plantas/metabolismo
19.
Photosynth Res ; 140(1): 39-49, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30315435

RESUMO

The trimeric nature of the Fenna-Matthews-Olson (FMO) protein antenna complex from green sulfur phototrophic bacteria was investigated. Mutations were introduced into the protein at positions 142 and 198, which were chosen to destabilize the intra-trimer salt bridges between adjacent monomers. Strains bearing the mutations R142L, R198L, or their combination, exhibited altered optical absorption spectra of purified membranes and fluoresced more intensely than the wild type. In particular, the introduction of the R142L mutation resulted in slower culture growth rates, as well as an FMO complex that was not able to be isolated in appreciable quantities, while the R198L mutation yielded an FMO complex with increased sensitivity to sodium thiocyanate and Triton X-100 treatments. Native and denaturing PAGE experiments suggest that much of the FMO complexes in the mutant strains pool with the insoluble material upon membrane solubilization with n-dodecyl ß-D-maltoside, a mild nonionic detergent. Taken together, our results suggest that the quaternary structure of the FMO complex, the homotrimer, is an important factor in the maintenance of the complex's tertiary structure.


Assuntos
Proteínas de Bactérias/química , Bacterioclorofilas/química , Chlorobi/química , Complexos de Proteínas Captadores de Luz/química , Estrutura Quaternária de Proteína , Substituição de Aminoácidos , Membrana Celular/efeitos da radiação , Chlorobi/efeitos da radiação , Modelos Moleculares , Complexos Multiproteicos , Mutação , Fotossíntese , Estabilidade Proteica
20.
Biochim Biophys Acta Bioenerg ; 1860(2): 147-154, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30537470

RESUMO

During the millions of years of evolution, photosynthetic organisms have adapted to almost all terrestrial and aquatic habitats, although some environments are obviously more suitable for photosynthesis than others. Photosynthetic organisms living in low-light conditions require on the one hand a large light-harvesting apparatus to absorb as many photons as possible. On the other hand, the excitation trapping time scales with the size of the light-harvesting system, and the longer the distance over which the formed excitations have to be transferred, the larger the probability to lose excitations. Therefore a compromise between photon capture efficiency and excitation trapping efficiency needs to be found. Here we report results on the whole cells of the green sulfur bacterium Chlorobaculum tepidum. Its efficiency of excitation energy transfer and charge separation enables the organism to live in environments with very low illumination. Using fluorescence measurements with picosecond resolution, we estimate that despite a rather large size and complex composition of its light-harvesting apparatus, the quantum efficiency of its photochemistry is around ~87% at 20 °C, ~83% at 45 °C, and about ~81% at 77 K when part of the excitation energy is trapped by low-energy bacteriochlorophyll a molecules. The data are evaluated using target analysis, which provides further insight into the functional organization of the low-light adapted photosynthetic apparatus.


Assuntos
Chlorobi/fisiologia , Transferência de Energia/fisiologia , Fotoquímica , Fotossíntese , Adaptação Fisiológica , Bacterioclorofila A/fisiologia , Fluorescência , Fluorometria/métodos , Complexos de Proteínas Captadores de Luz/metabolismo
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