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1.
BMC Genomics ; 20(1): 358, 2019 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-31072330

RESUMO

BACKGROUND: In natural environments, bacteria must frequently cope with extremely scarce nutrients. Most studies focus on bacterial growth in nutrient replete conditions, while less is known about the stationary phase. Here, we are interested in global gene expression throughout all growth phases, including the adjustment to deep stationary phase. RESULTS: We monitored both the transcriptome and the proteome in cultures of the alphaproteobacterium Rhodobacter sphaeroides, beginning with the transition to stationary phase and at different points of the stationary phase and finally during exit from stationary phase (outgrowth) following dilution with fresh medium. Correlation between the transcriptomic and proteomic changes was very low throughout the growth phases. Surprisingly, even in deep stationary phase, the abundance of many proteins continued to adjust, while the transcriptome analysis revealed fewer adjustments. This pattern was reversed during the first 90 min of outgrowth, although this depended upon the duration of the stationary phase. We provide a detailed analysis of proteomic changes based on the clustering of orthologous groups (COGs), and compare these with the transcriptome. CONCLUSIONS: The low correlation between transcriptome and proteome supports the view that post-transcriptional processes play a major role in the adaptation to growth conditions. Our data revealed that many proteins with functions in transcription, energy production and conversion and the metabolism and transport of amino acids, carbohydrates, lipids, and secondary metabolites continually increased in deep stationary phase. Based on these findings, we conclude that the bacterium responds to sudden changes in environmental conditions by a radical and rapid reprogramming of the transcriptome in the first 90 min, while the proteome changes were modest. In response to gradually deteriorating conditions, however, the transcriptome remains mostly at a steady state while the bacterium continues to adjust its proteome. Even long after the population has entered stationary phase, cells are still actively adjusting their proteomes.


Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Variação Genética , Proteoma/análise , Rhodobacter sphaeroides/crescimento & desenvolvimento , Transcriptoma , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/metabolismo
2.
J Bacteriol ; 201(4)2019 02 15.
Artigo em Inglês | MEDLINE | ID: mdl-30455284

RESUMO

Rhodobacter sphaeroides is able to use 3-hydroxypropionate as the sole carbon source through the reductive conversion of 3-hydroxypropionate to propionyl coenzyme A (propionyl-CoA). The ethylmalonyl-CoA pathway is not required in this process because a crotonyl-CoA carboxylase/reductase (Ccr)-negative mutant still grew with 3-hydroxypropionate. Much to our surprise, a mutant defective for another specific enzyme of the ethylmalonyl-CoA pathway, mesaconyl-CoA hydratase (Mch), lost its ability for 3-hydroxypropionate-dependent growth. Interestingly, the Mch-deficient mutant was rescued either by introducing an additional ccr in-frame deletion that resulted in the blockage of an earlier step in the pathway or by heterologously expressing a gene encoding a thioesterase (YciA) that can act on several CoA intermediates of the ethylmalonyl-CoA pathway. The mch mutant expressing yciA metabolized only less than half of the 3-hydroxypropionate supplied, and over 50% of that carbon was recovered in the spent medium as free acids of the key intermediates mesaconyl-CoA and methylsuccinyl-CoA. A gradual increase in growth inhibition due to the blockage of consecutive steps of the ethylmalonyl-CoA pathway by gene deletions suggests that the growth defects were due to the titration of free CoA and depletion of the CoA pool in the cell rather than to detrimental effects arising from the accumulation of a specific metabolite. Recovery of carbon in mesaconate for the wild-type strain expressing yciA demonstrated that carbon flux through the ethylmalonyl-CoA pathway occurs during 3-hydroxypropionate-dependent growth. A possible role of the ethylmalonyl-CoA pathway is proposed that functions outside its known role in providing tricarboxylic acid intermediates during acetyl-CoA assimilation.IMPORTANCE Mutant analysis is an important tool utilized in metabolic studies to understand which role a particular pathway might have under certain growth conditions for a given organism. The importance of the enzyme and of the pathway in which it participates is discretely linked to the resulting phenotype observed after mutation of the corresponding gene. This work highlights the possibility of incorrectly interpreting mutant growth results that are based on studying a single unit (gene and encoded enzyme) of a metabolic pathway rather than the pathway in its entirety. This work also hints at the possibility of using an enzyme as a drug target although the enzyme may participate in a nonessential pathway and still be detrimental to the cell when inhibited.


Assuntos
Acil Coenzima A/metabolismo , Ácido Láctico/análogos & derivados , Redes e Vias Metabólicas/genética , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo , Acil Coenzima A/deficiência , Carbono/metabolismo , Deleção de Genes , Ácido Láctico/metabolismo , Análise do Fluxo Metabólico
3.
Colloids Surf B Biointerfaces ; 172: 362-371, 2018 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-30189387

RESUMO

Biological processes using microorganisms for nanoparticle synthesis are appealing as eco-friendly nanofactories. The response of the photosynthetic bacterium Rhodobacter sphaeroides to gold exposure and its reducing capability of Au(III) to produce stable gold nanoparticles (AuNPs), using metabolically active bacteria and quiescent biomass, is reported in this study. In the former case, bacterial cells were grown in presence of gold chloride at physiological pH. Gold exposure was found to cause a significant increase of the lag-phase duration at concentrations higher than 10 µM, suggesting the involvement of a resistance mechanism activated by Au(III). Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM/EDS) analysis of bacterial cells confirmed the extracellular formation of AuNPs. Further studies were carried out on metabolically quiescent biomass incubated with gold chloride solution. The biosynthesized AuNPs were spherical in shape with an average size of 10 ±â€¯3 nm, as analysed by Transmission Electron Microscopy (TEM). The nanoparticles were hydrophilic and stable against aggregation for several months. In order to identify the functional groups responsible for the reduction and stabilization of nanoparticles, AuNPs were analysed by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), X-ray Fluorescence Spectrometry (XRF) and X-ray Absorption Spectroscopy (XAS) measurements. The obtained results indicate that gold ions bind to functional groups of cell membrane and are subsequently reduced by reducing sugars to gold nanoparticles and capped by a protein/peptide coat. Gold nanoparticles demonstrated to be efficient homogeneous catalysts in the degradation of nitroaromatic compounds.


Assuntos
Ouro/toxicidade , Nanopartículas Metálicas/toxicidade , Fotossíntese , Rhodobacter sphaeroides/metabolismo , Anaerobiose , Biomassa , Catálise , Nanopartículas Metálicas/ultraestrutura , Fotossíntese/efeitos dos fármacos , Rhodobacter sphaeroides/efeitos dos fármacos , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/ultraestrutura
4.
J Environ Sci (China) ; 70: 11-19, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30037398

RESUMO

This study aimed to increase bacterial growth and 5-aminolevulinic acid (ALA) biosynthesis of Rhodobacter sphaeroides in wastewater treatment through adding ferrous ion (Fe2+). Results demonstrated that Fe2+ effectively enhanced the biomass production and ALA yield of R. sphaeroides. Moreover, the optimal Fe2+ dosage was found to be 400µmol/L, which was associated with the highest biomass of 4015.3mg/L and maximum ALA yield of 15.9mg/g-dry cell weight (mg/g-DCW). Mechanism analysis revealed that Fe2+ vastly improved Adenosine Triphosphate (ATP) production by up-regulating the nif gene expression, and increasing ATP enhanced the biomass and ALA yield by supplying energy for bacterial growth and ALA biosynthesis, respectively. Correlation analysis showed that the ALA and ATP yields had positive relation with nifA and nifU gene expression. In addition, the nifA and nifU gene expression displayed high consistency of co-transcription at the optimal Fe2+ dosage.


Assuntos
Proteínas de Bactérias/genética , Ácidos Levulínicos/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Eliminação de Resíduos Líquidos/métodos , Ferro/metabolismo , Rhodobacter sphaeroides/metabolismo , Fatores de Transcrição , Águas Residuárias/microbiologia
5.
BMC Microbiol ; 18(1): 18, 2018 02 27.
Artigo em Inglês | MEDLINE | ID: mdl-29486719

RESUMO

BACKGROUND: A major role of the PhyR-NepR-σ(EcfG) cascade in the general stress response was demonstrated for some bacterial species and considered as conserved in Alphaproteobacteria. The σ(EcfG) factor activates its target genes in response to diverse stresses and NepR represents its anti-sigma factor. PhyR comprises a response regulator domain and a sigma factor domain and acts as anti-sigma factor antagonist. The facultative phototrophic alphaproteobacterium Rhodobacter sphaeroides harbours a PhyR homolog in the same genomic context as found in other members of this class. RESULTS: Our study reveals increased expression of the phyR gene in response to superoxide, singlet oxygen, and diamide and also an effect of PhyR on rpoE expression. RpoE has a central role in mounting the response to singlet oxygen in R. sphaeroides. Despite these findings a mutant lacking PhyR was not significantly impeded in resistance to oxidative stress, heat stress or osmotic stress. However a role of PhyR in membrane stress is demonstrated. CONCLUSION: These results support the view that the effect of the PhyR-NepR-σ(EcfG) cascade on diverse stress responses varies among members of the Alphaproteobacteria. In the facultative phototroph Rhodobacter sphaeroides PhyR plays no major role in the general stress or the oxidative stress response but rather has a more specialized role in defense of membrane stress.


Assuntos
Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/metabolismo , Fator sigma/genética , Fator sigma/metabolismo , Estresse Fisiológico/genética , Estresse Fisiológico/fisiologia , Membrana Celular , Regulação Bacteriana da Expressão Gênica , Genes Bacterianos/genética , Loci Gênicos , Resposta ao Choque Térmico , Pressão Osmótica , Estresse Oxidativo , Oxigênio , Domínios Proteicos , RNA Mensageiro/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Deleção de Sequência , Transcriptoma
6.
Biosci Biotechnol Biochem ; 82(1): 148-151, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29297256

RESUMO

Growth inhibition of Rhodobacter sphaeroides f. sp. denitrificans IL106 by nitrite under anaerobic-light conditions became less pronounced when the gene encoding nitrite reductase was deleted. Growth of another deletion mutant of the genes encoding nitric oxide reductase was severely suppressed by nitrite. Our results suggest that nitrite reductase increases the sensitivity to nitrite through the production of nitric oxide.


Assuntos
Nitritos/química , Rhodobacter sphaeroides/efeitos dos fármacos , Deleção de Genes , Nitrito Redutases/genética , Nitritos/farmacologia , Oxirredução , Rhodobacter sphaeroides/citologia , Rhodobacter sphaeroides/crescimento & desenvolvimento
7.
Enzyme Microb Technol ; 110: 1-7, 2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29310850

RESUMO

In this study, distillery wastewater was treated by dark fermentation or photofermentation alone, and by sequential dark and photofermentation processes using anaerobic saccharolytic consortium and purple nonsulfur bacteria. Combination of dark and photofermentation resulted in the maximal H2 yield of 17.6L/L of distillery waste with chemical oxygen demand 40g/L. It is equivalent to 205kJ/L distillery wastewater and corresponds to recovery of approximately 4-8% of energy consumed during ethanol production. Optimal performance of photofermentation was observed at 20% concentration of pre-fermented distillery waste. In photofermentation, the range of the suitable distillery waste concentrations was extended and the H2 yield was improved by choosing the tolerant strain of purple bacteria Rhodobacter sphaeroides B-3059. After two stages, organic acids and sugars were completely consumed that means wastewater treatment concomitant to H2 production.


Assuntos
Fermentação , Hidrogênio/metabolismo , Rhodobacter capsulatus/metabolismo , Rhodobacter sphaeroides/metabolismo , Águas Residuárias/microbiologia , Concentração de Íons de Hidrogênio , Luz , Rhodobacter capsulatus/crescimento & desenvolvimento , Rhodobacter capsulatus/efeitos da radiação , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/efeitos da radiação , Águas Residuárias/química
8.
Proc Natl Acad Sci U S A ; 114(41): 10906-10911, 2017 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-28935692

RESUMO

The native core light-harvesting complex (LH1) from the thermophilic purple phototrophic bacterium Thermochromatium tepidum requires Ca2+ for its thermal stability and characteristic absorption maximum at 915 nm. To explore the role of specific amino acid residues of the LH1 polypeptides in Ca-binding behavior, we constructed a genetic system for heterologously expressing the Tch. tepidum LH1 complex in an engineered Rhodobacter sphaeroides mutant strain. This system contained a chimeric pufBALM gene cluster (pufBA from Tch. tepidum and pufLM from Rba. sphaeroides) and was subsequently deployed for introducing site-directed mutations on the LH1 polypeptides. All mutant strains were capable of phototrophic (anoxic/light) growth. The heterologously expressed Tch. tepidum wild-type LH1 complex was isolated in a reaction center (RC)-associated form and displayed the characteristic absorption properties of this thermophilic phototroph. Spheroidene (the major carotenoid in Rba. sphaeroides) was incorporated into the Tch. tepidum LH1 complex in place of its native spirilloxanthins with one carotenoid molecule present per αß-subunit. The hybrid LH1-RC complexes expressed in Rba. sphaeroides were characterized using absorption, fluorescence excitation, and resonance Raman spectroscopy. Site-specific mutagenesis combined with spectroscopic measurements revealed that α-D49, ß-L46, and a deletion at position 43 of the α-polypeptide play critical roles in Ca binding in the Tch. tepidum LH1 complex; in contrast, α-N50 does not participate in Ca2+ coordination. These findings build on recent structural data obtained from a high-resolution crystallographic structure of the membrane integrated Tch. tepidum LH1-RC complex and have unambiguously identified the location of Ca2+ within this key antenna complex.


Assuntos
Proteínas de Bactérias/metabolismo , Cálcio/metabolismo , Chromatiaceae/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Rhodobacter sphaeroides/metabolismo , Proteínas de Bactérias/genética , Sítios de Ligação , Carotenoides/metabolismo , Chromatiaceae/genética , Chromatiaceae/crescimento & desenvolvimento , Complexos de Proteínas Captadores de Luz/química , Complexos de Proteínas Captadores de Luz/genética , Modelos Moleculares , Fotossíntese , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/genética , Ligação Proteica , Conformação Proteica , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/crescimento & desenvolvimento , Relação Estrutura-Atividade
9.
J Phys Chem B ; 121(32): 7571-7585, 2017 08 17.
Artigo em Inglês | MEDLINE | ID: mdl-28719215

RESUMO

This spectroscopic study investigates the origin of the transient feature of the S* excited state of carotenoids bound in LH1 complexes from purple bacteria. The studies were performed on two RC-LH1 complexes from Rba. sphaeroides strains that bound carotenoids with different carbon-carbon double bond conjugation N, neurosporene (N = 9) and spirilloxanthin (N = 13). The S* transient spectral feature, originally associated with an elusive and optically silent excited state of spirilloxanthin in the LH1 complex, may be successfully explained and mimicked without involving any unknown electronic state. The spectral and temporal characteristics of the S* feature suggest that it is associated with triplet-triplet annihilation of carotenoid triplets formed after direct excitation of the molecule via a singlet fission mechanism. Depending on pigment homogeneity and carotenoid assembly in the LH1 complex, the spectro-temporal component associated with triplet-triplet annihilation may simply resolve a pure T-S spectrum of a carotenoid. In some cases (like spirilloxanthin), the T-S feature will also be accompanied by a carotenoid Stark spectrum and/or residual transient absorption of minor carotenoid species bound into LH1 antenna complex.


Assuntos
Carotenoides/química , Complexos de Proteínas Captadores de Luz/química , Rhodobacter sphaeroides/metabolismo , Carotenoides/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismo , Fotossíntese , Teoria Quântica , Rhodobacter sphaeroides/crescimento & desenvolvimento , Espectrometria de Fluorescência , Espectrofotometria , Xantofilas/química
10.
RNA Biol ; 14(11): 1627-1637, 2017 11 02.
Artigo em Inglês | MEDLINE | ID: mdl-28692405

RESUMO

The function of 6S RNA, a global regulator of transcription, was studied in the photosynthetic α-proteobacterium Rhodobacter sphaeroides. The cellular levels of R. sphaeroides 6S RNA peak toward the transition to stationary phase and strongly decrease during extended stationary phase. The synthesis of so-called product RNA transcripts (mainly 12-16-mers) on 6S RNA as template by RNA polymerase was found to be highest in late exponential phase. Product RNA ≥ 13-mers are expected to trigger the dissociation of 6S RNA:RNA polymerase complexes. A 6S RNA deletion in R. sphaeroides had no impact on growth under various metabolic and oxidative stress conditions (with the possible exception of tert-butyl hydroperoxide stress). However, the 6S RNA knockout resulted in a robust growth defect under high salt stress (0.25 M NaCl). Remarkably, the sspA gene encoding the putative salt stress-induced membrane protein SspA and located immediately downstream of the 6S RNA (ssrS) gene on the antisense strand was expressed at elevated levels in the ΔssrS strain when grown in the presence of 250 mM NaCl.


Assuntos
Adesinas Bacterianas/genética , Regulação Bacteriana da Expressão Gênica , RNA Bacteriano/genética , RNA Mensageiro/genética , RNA não Traduzido/genética , Rhodobacter sphaeroides/genética , Adesinas Bacterianas/metabolismo , RNA Polimerases Dirigidas por DNA/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Deleção de Genes , Fenótipo , RNA Bacteriano/metabolismo , RNA Mensageiro/metabolismo , RNA não Traduzido/metabolismo , Rhodobacter sphaeroides/efeitos dos fármacos , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo , Cloreto de Sódio/farmacologia , Estresse Fisiológico , Transcrição Genética
11.
Water Sci Technol ; 75(11-12): 2489-2498, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28617267

RESUMO

Rhodobacter sphaeroides was used for bioremediation of wastewater polluted with cadmium (Cd) and zinc (Zn). The tolerance of the microorganism to selected heavy metals (HMs), as well as the effects of pH, temperature and inoculum size on the removal rate, was investigated. The remediation effects of R. sphaeroides were analysed at different initial concentrations of HMs. Bioremediation mechanisms were thoroughly discussed based on the results from the cell characterisation analysis. Cd and Zn could inhibit the growth of R. sphaeroides. However, Cd was more toxic than Zn, with corresponding EC50 values of 5.34 and 69.79 mg L-1. Temperature and pH had greater influence on the removal rate of HMs than inoculum size. The optimal conditions for temperature and pH were 35 °C-40 °C and pH 7, respectively. Initial concentration of HMs and remediation time also affected the removal rate. Rhodobacter sphaeroides had a relatively higher remediation effect under the present experimental conditions. The removal rates for Cd and Zn reached 97.92% and 97.76%, respectively. Results showed that biosorption and HM precipitation were the main bioremediation mechanisms. This information is necessary to better understand the removal mechanism of R. sphaeroides, and is significant for its pilot test and future practical application.


Assuntos
Cádmio/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo , Águas Residuárias/análise , Poluentes Químicos da Água/metabolismo , Zinco/metabolismo , Biodegradação Ambiental , Microscopia Eletrônica de Varredura , Espectroscopia de Infravermelho com Transformada de Fourier
12.
Nat Commun ; 8: 13972, 2017 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-28054547

RESUMO

Photosynthesis uses a limited range of the solar spectrum, so enhancing spectral coverage could improve the efficiency of light capture. Here, we show that a hybrid reaction centre (RC)/yellow fluorescent protein (YFP) complex accelerates photosynthetic growth in the bacterium Rhodobacter sphaeroides. The structure of the RC/YFP-light-harvesting 1 (LH1) complex shows the position of YFP attachment to the RC-H subunit, on the cytoplasmic side of the RC complex. Fluorescence lifetime microscopy of whole cells and ultrafast transient absorption spectroscopy of purified RC/YFP complexes show that the YFP-RC intermolecular distance and spectral overlap between the emission of YFP and the visible-region (QX) absorption bands of the RC allow energy transfer via a Förster mechanism, with an efficiency of 40±10%. This proof-of-principle study demonstrates the feasibility of increasing spectral coverage for harvesting light using non-native genetically-encoded light-absorbers, thereby augmenting energy transfer and trapping in photosynthesis.


Assuntos
Proteínas de Bactérias/metabolismo , Luz , Proteínas Luminescentes/metabolismo , Fotossíntese , Complexo de Proteína do Fotossistema I/metabolismo , Rhodobacter sphaeroides/fisiologia , Western Blotting , Transferência Ressonante de Energia de Fluorescência , Microscopia Eletrônica , Microscopia de Fluorescência , Modelos Biológicos , Projetos Piloto , Teoria Quântica , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo , Análise Espectral/métodos
13.
Appl Microbiol Biotechnol ; 100(24): 10649-10658, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27838838

RESUMO

Cell number of Clostridium butyricum and Rhodobacter sphaeroides in co-culture was measured using q-PCR approach. During efficient H2 photoproduction from starch (6.2 mol H2/mol glucose), Clostridia growth and starch-hydrolyzing activity was partly suppressed. Apparently, the effect of R. sphaeroides towards C. butyricum was not attributed to altered Eh or pH values in the presence of purple bacteria. Further, disk-diffusion test proved that R. sphaeroides was capable of producing inhibitors against another purple bacterium, Rhodospirillum rubrum, but not against C. butyricum. We suggested that at initial cell number ratio C. butyricum:R. sphaeroides 1:1 purple bacteria outcompeted C. butyricum for yeast extract at its low concentration (80 mg/L). Under these conditions, the H2 yield was rather high (5.7 mol/mol). When the yeast extract concentration increased to 320 mg/L, this process was replaced by the low-yield H2 production (1.8 mol/mol) characteristic of Clostridia. However, increased percentage of purple bacteria in inoculum under these conditions prevented this shift. The outcome of competition depended on both the yeast extract concentration and cell number ratio. Apparently, the competition for yeast extract helped to maintain balance between fast-growing C. butyricum and slower-growing R. sphaeroides for efficient H2 photoproduction.


Assuntos
Clostridium butyricum/crescimento & desenvolvimento , Clostridium butyricum/metabolismo , Hidrogênio/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo , Antibiose , Carga Bacteriana , Técnicas de Cocultura , Meios de Cultura/química , Concentração de Íons de Hidrogênio , Reação em Cadeia da Polimerase em Tempo Real , Amido/metabolismo
14.
J Phys Chem B ; 120(43): 11123-11131, 2016 11 03.
Artigo em Inglês | MEDLINE | ID: mdl-27726397

RESUMO

Carotenoids are a class of natural pigments present in all phototrophic organisms, mainly in their light-harvesting proteins in which they play roles of accessory light absorbers and photoprotectors. Extensive time-resolved spectroscopic studies of these pigments have revealed unexpectedly complex photophysical properties, particularly for carotenoids in light-harvesting LH2 complexes from purple bacteria. An ambiguous, optically forbidden electronic excited state designated as S* has been postulated to be involved in carotenoid excitation relaxation and in an alternative carotenoid-to-bacteriochlorophyll energy transfer pathway, as well as being a precursor of the carotenoid triplet state. However, no definitive and satisfactory origin of the carotenoid S* state in these complexes has been established, despite a wide-ranging series of studies. Here, we resolve the ambiguous origin of the carotenoid S* state in LH2 complex from Rba. sphaeroides by showing that the S* feature can be seen as a combination of ground state absorption bleaching of the carotenoid pool converted to cations and the Stark spectrum of neighbor neutral carotenoids, induced by temporal electric field brought by the carotenoid cation-bacteriochlorophyll anion pair. These findings remove the need to assign an S* state, and thereby significantly simplify the photochemistry of carotenoids in these photosynthetic antenna complexes.


Assuntos
Carotenoides/química , Complexos de Proteínas Captadores de Luz/química , Teoria Quântica , Rhodobacter sphaeroides/química , Carotenoides/metabolismo , Complexos de Proteínas Captadores de Luz/isolamento & purificação , Complexos de Proteínas Captadores de Luz/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/metabolismo
15.
J Photochem Photobiol B ; 162: 592-596, 2016 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-27479839

RESUMO

The present work was focused on the effects of low-intensity (the flux capacity was of 0.06mWcm(-2)) electromagnetic irradiation (EMI) of extremely high frequencies or millimeter waves on the growth and hydrogen (H2) photoproduction by purple non-sulfur bacteria Rhodobacter sphaeroides MDC6521 (from Armenian mineral springs). After exposure of R. sphaeroides, grown under anaerobic conditions upon illumination, to EMI (51.8GHz and 53.0GHz) for 15min an increase of specific growth rate by ~1.2-fold, in comparison with control (non-irradiated cells), was obtained. However, the effect of EMI depends on the duration of irradiation: the exposure elongation up to 60min caused the delay of the growth lag phase and the decrease specific growth rate by ~1.3-fold, indicating the bactericidal effect of EMI. H2 yield of the culture, irradiated by EMI for 15min, determined during 72h growth, was ~1.2-fold higher than H2 yield of control cells, whereas H2 production by cultures, irradiated by EMI for 60min was not observed during 72h growth. This difference in the effects of extremely high frequency EMI indicates a direct effect of radiation on the membrane transfer and the enzymes of these bacteria. Moreover, EMI increased DCCD-inhibited H(+) fluxes across the bacterial membrane and DCCD-sensitive ATPase activity of membrane vesicles, indicating that the proton FoF1-ATPase is presumably a basic target for extremely high frequency EMI related to H2 production by cultures.


Assuntos
Radiação Eletromagnética , Hidrogênio/metabolismo , Rhodobacter sphaeroides/metabolismo , Proteínas de Bactérias/metabolismo , Parede Celular/metabolismo , Oxirredução , ATPases Translocadoras de Prótons/metabolismo , Rhodobacter sphaeroides/crescimento & desenvolvimento , Rhodobacter sphaeroides/efeitos da radiação
16.
FEBS Lett ; 590(16): 2515-26, 2016 08.
Artigo em Inglês | MEDLINE | ID: mdl-27325608

RESUMO

The structure of the bacterial photosynthetic reaction center (RC) reveals symmetry-related electron transfer (ET) pathways, but only one path is used in native RCs. Analogous mutations have been made in two Rhodobacter (R.) species. A glutamic acid at position 133 in the M subunit increases transmembrane charge separation via the naturally inactive (B-side) path through impacts on primary ET in mutant R. sphaeroidesRCs. Prior work showed that the analogous substitution in the R. capsulatusRC also increases B-side activity, but mainly affects secondary ET. The overall yields of transmembrane ET are similar, but enabled in fundamentally different ways.


Assuntos
Transporte de Elétrons/genética , Fotossíntese/genética , Rhodobacter capsulatus/genética , Rhodobacter sphaeroides/genética , Substituição de Aminoácidos , Cinética , Mutagênese Sítio-Dirigida , Mutação , Rhodobacter capsulatus/crescimento & desenvolvimento , Rhodobacter sphaeroides/crescimento & desenvolvimento
17.
Photosynth Res ; 130(1-3): 307-316, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27034065

RESUMO

The composition of photosynthetic apparatus of Rhodobacter sphaeroides wild strain 2.4.1 and its LHII-deficient mutant DBCΩ was compared. The absence of LHII in the mutant was confirmed by comparison of chromatophores spectra and by the absence of electrophoretic band corresponding to LHII complex. Continuous turbidostat cultures of wild strain and its LHII-deficient mutant were compared in response to different light intensities. Cultures were grown using lactate, mixture of lactate and acetate or succinate as carbon source. For comparative analysis, an approximation of experimental data by Monod and Gompertz equations were used. Cultures of DBCΩ had lower growth rates than wild strain when grown on lactate as electron donor and carbon source. Cultures of both strains grown on lactate and acetate or on succinate had similar growth rates. The cultures showed maximum growth rates when grown with succinate. Bacteriochlorophyll a content increased in both strains with decrease of incident light intensity. However, the variation of Bchl a content in wild strain was much more significant. Under light-limiting conditions, bacteriochlorophyll a content in DBCΩ was 4-5 times lower than in the wild strain. Under light-saturating conditions, it was only 1.5-2.5 times lower. Growing with lactate or with lactate and acetate, the mutant switched from light limitation under low light intensities to limitation by organic acids under higher light, whereas the parental strain had similar switch of limiting factor only when growing with lactate and acetate mixture. DBCΩ mutant has higher minimal light intensity enabling growth on any organic acid as a substrate. When growing with lactate or with lactate and acetate, the mutant reached maximum growth rate at lower light intensities than the wild strain. This phenomenon was observed for the first time. Taking into account the concentration of BChl a under light-limiting conditions, the thickness of the suspension capable of effective light absorption could be increased by 4-5 times, which is favorable for intensive cultivation.


Assuntos
Rhodobacter sphaeroides/efeitos da radiação , Acetatos/metabolismo , Proteínas de Bactérias/fisiologia , Bacterioclorofila A/metabolismo , Ácido Láctico/metabolismo , Luz , Complexos de Proteínas Captadores de Luz/deficiência , Complexos de Proteínas Captadores de Luz/metabolismo , Complexos de Proteínas Captadores de Luz/fisiologia , Complexo de Proteína do Fotossistema II/fisiologia , Rhodobacter sphaeroides/efeitos dos fármacos , Rhodobacter sphaeroides/crescimento & desenvolvimento , Succinatos/metabolismo
18.
J Microbiol Biotechnol ; 26(5): 959-66, 2016 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-26869605

RESUMO

Chlorophyll synthase (ChlG) and bacteriochlorophyll synthase (BchG) have a high degree of substrate specificity. The BchG mutant of Rhodobacter sphaeroides, BG1 strain, is photosynthetically incompetent. When BG1 harboring chlG of Synechocystis sp. PCC 6803 was cultured photoheterotrophically, colonies arose at a frequency of approximately 10(-8). All the suppressor mutants were determined to have the same mutational change, ChlGI44F. The mutated enzyme ChlGI44F showed BchG activity. Remarkably, BchGF28I, which has the substitution of F at the corresponding 28(th) residue to I, showed ChlG activity. The Km values of ChlGI44F and BchGF28I for their original substrates, chlorophyllide (Chlide) a and bacteriochlorophyllide (Bchlide) a, respectively, were not affected by the mutations, but the Km values of ChlGI44F and BchGF28I for the new substrates Bchlide a and Chlide a, respectively, were more than 10-fold larger than those for their original substrates, suggesting the lower affinities for new substrates. Taken together, I44 and F28 are important for the substrate specificities of ChlG and BchG, respectively. The BchG activity of ChlGI44F and the ChlG activity of BchGF28I further suggest that ChlG and BchG are evolutionarily related enzymes.


Assuntos
Carbono-Oxigênio Ligases/deficiência , Rhodobacter sphaeroides/enzimologia , Rhodobacter sphaeroides/crescimento & desenvolvimento , Synechocystis/enzimologia , Synechocystis/genética , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Bacterioclorofila A/biossíntese , Bacterioclorofila A/química , Bacterioclorofila A/metabolismo , Carbono-Oxigênio Ligases/genética , Carbono-Oxigênio Ligases/metabolismo , Clorofila/metabolismo , Ativação Enzimática , Processos Heterotróficos , Mutagênese Sítio-Dirigida , Fotossíntese , Processos Fototróficos , Rhodobacter sphaeroides/genética , Especificidade por Substrato
19.
Appl Biochem Biotechnol ; 179(3): 444-58, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-26875086

RESUMO

Microbial 5-aminolevulinic acid (ALA) produced from wastewater is considered as potential renewable energy. However, many hurdles are needed to be overcome such as the regulation of key influencing factors on ALA yield. Biomass and ALA production by Rhodobacter sphaeroides was optimized using response surface methodology. The culturing medium was artificial volatile fatty acids wastewater. Three additives were optimized, namely succinate and glycine that are precursors of ALA biosynthesis, and D-glucose that is an inhibitor of ALA dehydratase. The optimal conditions were achieved by analyzing the response surface plots. Statistical analysis showed that succinate at 8.56 mmol/L, glycine at 5.06 mmol/L, and D-glucose at 7.82 mmol/L were the best conditions. Under these optimal conditions, the highest biomass production and ALA yield of 3.55 g/L and 5.49 mg/g-biomass were achieved. Subsequent verification experiments at optimal values had the maximum biomass production of 3.41 ± 0.002 g/L and ALA yield of 5.78 ± 0.08 mg/g-biomass.


Assuntos
Ácido Aminolevulínico/metabolismo , Biomassa , Ácidos Graxos Voláteis/farmacologia , Ácido Aminolevulínico/química , Ácidos Graxos Voláteis/química , Regulação Bacteriana da Expressão Gênica , Sintase do Porfobilinogênio/química , Rhodobacter sphaeroides/química , Rhodobacter sphaeroides/efeitos dos fármacos , Rhodobacter sphaeroides/crescimento & desenvolvimento , Propriedades de Superfície , Águas Residuárias/química
20.
Microbiologyopen ; 4(5): 790-802, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-26235649

RESUMO

IscR proteins are known as transcriptional regulators for Fe-S biogenesis. In the facultatively phototrophic bacterium, Rhodobacter sphaeroides IscR is the product of the first gene in the isc-suf operon. A major role of IscR in R. sphaeroides iron-dependent regulation was suggested in a bioinformatic study (Rodionov et al., PLoS Comput Biol 2:e163, 2006), which predicted a binding site in the upstream regions of several iron uptake genes, named Iron-Rhodo-box. Most known IscR proteins have Fe-S clusters featuring (Cys)3 (His)1 ligation. However, IscR proteins from Rhodobacteraceae harbor only a single-Cys residue and it was considered unlikely that they can ligate an Fe-S cluster. In this study, the role of R. sphaeroides IscR as transcriptional regulator and sensor of the Fe-S cluster status of the cell was analyzed. A mutant lacking IscR is more impaired in growth under iron limitation than the wild-type and exhibits significantly increased ROS levels in iron-replete and iron-deplete conditions. Expression studies reveal that R. sphaeroides IscR in its cluster-bound form functions as transcriptional repressor of genes involved in iron metabolism by direct binding to the promoter region of genes preceded by the motif. A total of 110 genes are directly or indirectly affected by IscR. Furthermore, IscR possesses a unique Fe-S cluster ligation scheme with only a single cysteine involved.


Assuntos
Regulação Bacteriana da Expressão Gênica , Proteínas com Ferro-Enxofre/metabolismo , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Rhodobacter sphaeroides/genética , Rhodobacter sphaeroides/metabolismo , Meios de Cultura/química , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Bacteriano/metabolismo , Deleção de Genes , Perfilação da Expressão Gênica , Ferro/metabolismo , Dados de Sequência Molecular , Regiões Promotoras Genéticas , Ligação Proteica , Espécies Reativas de Oxigênio/análise , Regulon , Rhodobacter sphaeroides/crescimento & desenvolvimento , Análise de Sequência de DNA
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