bacteriochlorophylls and spheroidene

Light-harvesting 2 (LH2) antenna complexes augment the collection of solar energy in many phototrophic bacteria. Despite its frequent role as a model for such complexes, there has been no three-dimensional (3D) structure available for the LH2 from the purple phototroph

Topics: Bacterial Proteins; Bacteriochlorophyll A; Carotenoids; Cryoelectron Microscopy; Energy Transfer; Light-Harvesting Protein Complexes; Rhodobacter sphaeroides

Six variants of the LH2 antenna complex from Rba. sphaeroides, comprising the native B800-B850, B800-free LH2 (B850) and four LH2s with various (bacterio)chlorophylls reconstituted into the B800 site, have been investigated with static and time-resolved optical spectroscopies at room temperature and at 77 K. The study particularly focused on how reconstitution of a non-native (bacterio)chlorophylls affects excitation energy transfer between the naturally bound carotenoid spheroidene and artificially substituted pigments in the B800 site. Results demonstrate there is no apparent trend in the overall energy transfer rate from spheroidene to B850 bacteriochlorophyll a; however, a trend in energy transfer rate from the spheroidene S

Topics: Bacterial Proteins; Bacteriochlorophyll A; Bacteriochlorophylls; Carotenoids; Energy Transfer; Light-Harvesting Protein Complexes; Rhodobacter sphaeroides; Spectrometry, Fluorescence

A novel Gram-staining-negative, purple non-sulfur bacterium, strain AK41(T), was isolated from a sediment sample collected from Coringa mangrove forest, Andhra Pradesh, India. A red-brownish-coloured culture was obtained on modified Pfennig medium after enrichment with 2 % NaCl and 0.3 % pyruvate under 2000 lx illumination. Individual cells were ovoid-rod-shaped and non-motile. Bacteriochlorophyll a and carotenoids of the spheroidene series were present as photosynthetic pigments. Strain AK41(T) was halophilic and grew photoheterotrophically with a number of organic compounds as carbon sources and electron donors. It was unable to grow photoautotrophically. It did not utilize sulfide or thiosulfate as electron donors. The fatty acids were found to be dominated by C16 : 0 and C18 : 1ω7c. Strain AK41(T) contained phosphatidylglycerol, phosphatidylethanolamine, an unknown aminolipid and four unknown lipids as polar lipids. Q-10 was the predominant respiratory quinone. The DNA G+C content of strain AK41(T) was 68.9 mol%. 16S rRNA gene sequence analysis indicated that strain AK41(T) was a member of the genus Rhodovulum and was closely related to Rhodovulum sulfidophilum, with 96.0 % similarity to the type strain; the 16S rRNA gene sequence similarity to the type strains of other species of the genus Rhodovulum was 93.9-95.8 %. Phylogenetic analyses indicated that strain AK41(T) clustered with the type strains of Rhodovulum marinum, Rdv. kholense, Rdv. sulfidophilum and Rdv. visakhapatnamense with sequence similarity of 95.9-96.2 %. Based on data from the current study, strain AK41(T) is proposed to represent a novel species of the genus Rhodovulum, for which the name Rhodovulum mangrovi sp. nov. is proposed. The type strain of Rhodovulum mangrovi is AK41(T) ( = MTCC 11825(T) = JCM 19220(T)).

Topics: Avicennia; Bacterial Typing Techniques; Bacteriochlorophyll A; Base Composition; Carotenoids; DNA, Bacterial; Fatty Acids; Geologic Sediments; India; Molecular Sequence Data; Phylogeny; Pigmentation; Rhodovulum; RNA, Ribosomal, 16S; Sequence Analysis, DNA; Ubiquinone; Wetlands

A Rhodobacter capsulatus strain, designated XJ-1, isolated from saline soil, accumulated almost only one kind of bacteriochlorophyll a anaerobically in the light, aerobically in the light and dark, and the relative contents of the bacteriochlorophyll a were 44.61, 74.89, and 77.53% of the total pigments, respectively. A new purple pigment appeared only in aerobic-light grown cells, exhibited absorption maxima at 355, 389, 520, 621, and 755 nm, especially distinctly unusual peak at 621 nm, whereas vanished in anaerobic-light and in aerobic-dark culture. Spheroidene and OH-spheroidene predominated in anaerobic phototrophic cultures. Spheroidenone was the sole carotenoid when exposed to both light and oxygen. The second keto-carotenoids, OH-spheroidenone, presented only in aerobic-dark culture in addition to spheroidenone. Strain XJ-1 would be a good model organism for the further illustration of the regulation of bacteriochlorophyll biosynthesis gene expression in response to unique habitat.

Topics: Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Light; Mass Spectrometry; Oxygen; Pheophytins; Rhodobacter capsulatus; Salinity; Sodium Chloride; Soil; Soil Microbiology

Bacteriochlorophyll a with Ni(2+) replacing the central Mg(2+) ion was used as an ultrafast excitation energy dissipation center in reconstituted bacterial LH1 complexes. B870, a carotenoid-less LH1 complex, and B880, an LH1 complex containing spheroidene, were obtained via reconstitution from the subunits isolated from chromatophores of Rhodospirillum rubrum . Ni-substituted bacteriochlorophyll a added to the reconstitution mixture partially substituted the native pigment in both forms of LH1. The excited-state dynamics of the reconstituted LH1 complexes were probed by femtosecond pump-probe transient absorption spectroscopy in the visible and near-infrared spectral region. Spheroidene-binding B880 containing no excitation dissipation centers displayed complex dynamics in the time range of 0.1-10 ps, reflecting internal conversion and intersystem crossing in the carotenoid, exciton relaxation in BChl complement, and energy transfer from carotenoid to the latter. In B870, some aggregation-induced excitation energy quenching was present. The binding of Ni-BChl a to both B870 and B880 resulted in strong quenching of the excited states with main deexcitation lifetime of ca. 2 ps. The LH1 excited-state lifetime could be modeled with an intrinsic decay time constant in Ni-substituted bacteriochlorophyll a of 160 fs. The presence of carotenoid in LH1 did not influence the kinetics of energy trapping by Ni-BChl unless the carotenoid was directly excited, in which case the kinetics was limited by a slower carotenoid S1 to bacteriochlorophyll energy transfer.

Topics: Bacterial Proteins; Bacteriochlorophyll A; Carotenoids; Energy Transfer; Ions; Light-Harvesting Protein Complexes; Microscopy, Atomic Force; Nickel; Protochlorophyllide; Rhodospirillum rubrum; Spectrometry, Fluorescence; Time Factors

An oval to rod-shaped, Gram-stain-negative, phototrophic bacterium, strain JA738(T), was isolated from a sediment sample collected from a pink pond. Strain JA738(T) was non-motile and had vesicular-type intracellular photosynthetic membranes. Bacteriochlorophyll a and carotenoids of the spheroidene series were present as the major photosynthetic pigments. Strain JA738(T) required thiamine and pantothenate for growth. The major cellular fatty acids were C(18 : 1)ω7c, C(18 : 1)ω5c, C(18 : 0) and C(18 : 1)ω7c11-methyl; minor amounts of C(10 : 0) 3-OH and C(16 : 0) were also present. The major quinone was Q-10 and major polar lipids were phosphatidylglycerol, phosphatidylethanolamine and two unidentified sulfolipids (SL1-2). Phylogenetic analysis on the basis of 16S rRNA gene sequences showed that strain JA738(T) clustered with species of the genus Rhodovulum in the class Alphaproteobacteria. Strain JA738(T) was most closely related to Rhodovulum adriaticum DSM 2781(T) (96.4 % 16S rRNA gene sequence similarity) and other members of the genus Rhodovulum (<96.1 %). On the basis of phenotypic and molecular genetic evidence, it is proposed that strain JA738(T) should be classified as a novel species of the genus Rhodovulum for which the name Rhodovulum bhavnagarense sp. nov. is proposed. The type strain is JA738(T) ( = DSM 24766(T) = KCTC 15110(T)).

Topics: Bacterial Typing Techniques; Bacteriochlorophyll A; Carotenoids; DNA, Bacterial; Fatty Acids; Geologic Sediments; India; Molecular Sequence Data; Phylogeny; Ponds; Rhodovulum; RNA, Ribosomal, 16S; Sequence Analysis, DNA

Carotenoids are known to offer protection against the potentially damaging combination of light and oxygen encountered by purple phototrophic bacteria, but the efficiency of such protection depends on the type of carotenoid. Rhodobacter sphaeroides synthesizes spheroidene as the main carotenoid under anaerobic conditions whereas, in the presence of oxygen, the enzyme spheroidene monooxygenase catalyses the incorporation of a keto group forming spheroidenone. We performed ultrafast transient absorption spectroscopy on membranes containing reaction center-light-harvesting 1-PufX (RC-LH1-PufX) complexes and showed that when oxygen is present the incorporation of the keto group into spheroidene, forming spheroidenone, reconfigures the energy transfer pathway in the LH1, but not the LH2, antenna. The spheroidene/spheroidenone transition acts as a molecular switch that is suggested to twist spheroidenone into an s-trans configuration increasing its conjugation length and lowering the energy of the lowest triplet state so it can act as an effective quencher of singlet oxygen. The other consequence of converting carotenoids in RC-LH1-PufX complexes is that S(2)/S(1)/triplet pathways for spheroidene is replaced with a new pathway for spheroidenone involving an activated intramolecular charge-transfer (ICT) state. This strategy for RC-LH1-PufX-spheroidenone complexes maintains the light-harvesting cross-section of the antenna by opening an active, ultrafast S(1)/ICT channel for energy transfer to LH1 Bchls while optimizing the triplet energy for singlet oxygen quenching. We propose that spheroidene/spheroidenone switching represents a simple and effective photoprotective mechanism of likely importance for phototrophic bacteria that encounter light and oxygen.

Topics: Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Cell Membrane; Energy Transfer; Light; Light-Harvesting Protein Complexes; Molecular Structure; Oxygen; Proteobacteria; Rhodobacter sphaeroides; Spectrophotometry

Steady-state and ultrafast time-resolved optical spectroscopic investigations have been carried out at 293 and 10 K on LH2 pigment-protein complexes isolated from three different strains of photosynthetic bacteria: Rhodobacter (Rb.) sphaeroides G1C, Rb. sphaeroides 2.4.1 (anaerobically and aerobically grown), and Rps. acidophila 10050. The LH2 complexes obtained from these strains contain the carotenoids, neurosporene, spheroidene, spheroidenone, and rhodopin glucoside, respectively. These molecules have a systematically increasing number of pi-electron conjugated carbon-carbon double bonds. Steady-state absorption and fluorescence excitation experiments have revealed that the total efficiency of energy transfer from the carotenoids to bacteriochlorophyll is independent of temperature and nearly constant at approximately 90% for the LH2 complexes containing neurosporene, spheroidene, spheroidenone, but drops to approximately 53% for the complex containing rhodopin glucoside. Ultrafast transient absorption spectra in the near-infrared (NIR) region of the purified carotenoids in solution have revealed the energies of the S1 (2(1)Ag-)-->S2 (1(1)Bu+) excited-state transitions which, when subtracted from the energies of the S0 (1(1)Ag-)-->S2 (1(1)Bu+) transitions determined by steady-state absorption measurements, give precise values for the positions of the S1 (2(1)Ag-) states of the carotenoids. Global fitting of the ultrafast spectral and temporal data sets have revealed the dynamics of the pathways of de-excitation of the carotenoid excited states. The pathways include energy transfer to bacteriochlorophyll, population of the so-called S* state of the carotenoids, and formation of carotenoid radical cations (Car*+). The investigation has found that excitation energy transfer to bacteriochlorophyll is partitioned through the S1 (1(1)Ag-), S2 (1(1)Bu+), and S* states of the different carotenoids to varying degrees. This is understood through a consideration of the energies of the states and the spectral profiles of the molecules. A significant finding is that, due to the low S1 (2(1)Ag-) energy of rhodopin glucoside, energy transfer from this state to the bacteriochlorophylls is significantly less probable compared to the other complexes. This work resolves a long-standing question regarding the cause of the precipitous drop in energy transfer efficiency when the extent of pi-electron conjugation of the carotenoid is extended from ten to eleven conjugated ca

Topics: Algorithms; Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Cold Temperature; Energy Transfer; Kinetics; Light-Harvesting Protein Complexes; Models, Molecular; Rhodobacter sphaeroides; Rhodopseudomonas; Spectrometry, Fluorescence; Spectrophotometry; Spectroscopy, Near-Infrared; Temperature; Time Factors

In LH2 complexes of Rhodobacter sphaeroides the formation of a carotenoid radical cation has recently been observed upon photoexcitation of the carotenoid S2 state. To shed more light onto the yet unknown molecular mechanism leading to carotenoid radical formation in LH2, the interactions between carotenoid and bacteriochlorophyll in LH2 are investigated by means of quantum chemical calculations for three different carotenoids--neurosporene, spheroidene, and spheroidenone--using time-dependent density functional theory. Crossings of the calculated potential energy curve of the electron transfer state with the bacteriochlorophyll Qx state and the carotenoid S1 and S2 states occur along an intermolecular distance coordinate for neurosporene and spheroidene, but for spheroidenone no crossing of the electron transfer state with the carotenoid S1 state could be found. By comparison with recent experiments where no formation of a spheroidenone radical cation has been observed, a molecular mechanism for carotenoid radical cation formation is proposed in which it is formed via a vibrationally excited carotenoid S1 or S*state. Arguments are given why the formation of the carotenoid radical cation does not proceed via the Qx, S2, or higher excited electron transfer states.

Topics: Algorithms; Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Cations; Electron Transport; Energy Transfer; Free Radicals; Light; Light-Harvesting Protein Complexes; Protein Conformation; Proteobacteria; Quantum Theory; Rhodobacter sphaeroides; Time Factors

It is well-known that time-dependent density functional theory (TDDFT) yields substantial errors for the excitation energies of charge-transfer (CT) excited states, when approximate standard exchange-correlation (xc) functionals are used, for example, SVWN, BLYP, or B3LYP. Also, the correct 1/R asymptotic behavior of CT states with respect to a distance coordinate R between the separated charges of the CT state is not reproduced by TDDFT employing these xc-functionals. Here, we demonstrate by analysis of the TDDFT equations that the first failure is due to the self-interaction error in the orbital energies from the ground-state DFT calculation, while the latter is a similar self-interaction error in TDDFT arising through the electron transfer in the CT state. Possible correction schemes, such as inclusion of exact Hartree-Fock or exact Kohn-Sham exchange, as well as aspects of the exact xc-functional are discussed in this context. Furthermore, a practical approach is proposed which combines the benefits of TDDFT and configuration interaction singles (CIS) and which does not suffer from electron-transfer self-interaction. The latter approach is applied to a (1,4)-phenylene-linked zincbacteriochlorin-bacteriochlorin complex and to a bacteriochlorophyll-spheroidene complex, in which CT states may play important roles in energy and electron-transfer processes. The errors of TDDFT alone for the CT states are demonstrated, and reasonable estimates for the true excitation energies of these states are given.

Topics: Bacteriochlorophylls; Carotenoids; Electron Transport; Energy Transfer; Metalloporphyrins; Models, Chemical; Photosynthetic Reaction Center Complex Proteins; Porphyrins; Proteobacteria; Systems Theory; Time Factors

The dynamics of triplet energy transfer between the primary donor and the carotenoid were measured on several photosynthetic bacterial reaction center preparations from Rhodobacter sphaeroides: (a) wild-type strain 2.4.1, (b) strain R-26.1, (c) strain R-26.1 exchanged with 13(2)-hydroxy-[Zn]-bacteriochlorophyll at the accessory bacteriochlorophyll (BChl) sites and reconstituted with spheroidene and (d) strain R-26.1 exchanged with [3-vinyl]-13(2)-hydroxy-bacteriochlorophyll at the accessory BChl sites and reconstituted with spheroidene. The rise and decay times of the primary donor and carotenoid triplet-triplet absorption signals were monitored in the visible wavelength region between 538 and 555 nm as a function of temperature from 4 to 300 K. For the samples containing carotenoids, all of the decay times correspond well to the previously observed times for spheroidene (5 +/- 2 microseconds). The rise times of the carotenoid triplets were found in all cases to be biexponential and comprised of a strongly temperature-dependent component and a temperature-independent component. From a comparison of the behavior of the carotenoid-containing samples with that from the reaction center of the carotenoidless mutant Rb. sphaeroides R-26.1, the temperature-independent component has been assigned to the buildup of the primary donor triplet state resulting from charge recombination in the reaction center. Arrhenius plots of the buildup of the carotenoid triplet states were used to determine the activation energies for triplet energy transfer from the primary donor to the carotenoid. A model for the process of triplet energy transfer that is consistent with the data suggests that the activation barrier is strongly dependent on the triplet state energy of the accessory BChl pigment, BChlB.

Topics: Bacteriochlorophylls; Carotenoids; Energy Transfer; Light-Harvesting Protein Complexes; Photosynthetic Reaction Center Complex Proteins; Rhodobacter sphaeroides

Photosynthetic reaction centres (RCs) catalyze light-driven electron, transport across photosynthetic membranes. The photosynthetic bacterium Rhodobacter, sphaeroides is often used for studies of RCs, and three groups have determined the structure of its reaction centre. There are discrepancies between these structures, however, and to resolve these we have determined the structure to higher resolution than before, using a new crystal form.. The new structure provides a more detailed description of the Rb. sphaeroides RC, and allows us to compare it with the structure of the RC from Rhodopseudomonas viridis. We find no evidence to support most of the published differences in cofactor binding between the RCs from Rps. viridis and Rb. sphaeroides. Generally, the mode of cofactor binding is conserved, particularly along the electron transfer pathway. Substantial differences are only found at ring V of one bacteriochlorophyll of the 'special pair' and for the secondary quinone, QB. A water chain with a length of about 23 A including 14 water molecules extends from the QB to the cytoplasmic side of the RC.. The cofactor arrangement and the mode of binding to the protein seem to be very similar among the non-sulphur bacterial photosynthetic RCs. The functional role of the displaced QB molecule, which might be present as quinol, rather than quinone, is not yet clear. The newly discovered water chain to the QB binding site suggests a pathway for the protonation of the secondary quinone QB.

Topics: Bacteriochlorophylls; Carotenoids; Electron Transport; Iron; Light-Harvesting Protein Complexes; Models, Molecular; Molecular Structure; Pheophytins; Photosynthetic Reaction Center Complex Proteins; Protein Conformation; Protons; Quinones; Rhodobacter sphaeroides

The B800-to-B850 energy transfer time in the purified B800-850 light-harvesting complex of Rhodobacter sphaeroides 2.4.1 is determined to be 0.7 ps at room temperature. The electronic state dynamics of the principal carotenoid of this species, spheroidene, are examined, both in vivo and in vitro, by direct femtosecond time-resolved experiments and by fluorescence emission yield studies. Evidence is presented which suggests that carotenoid-to-bacteriochlorophyll energy transfer may occur directly from the initially excited carotenoid S2 state, as well as from the carotenoid S1 state. Further support for this conjecture is obtained from calculations of energy transfer rates from the carotenoid S2 state. Previous measurements of in vivo carotenoid and B800 dynamics are discussed in light of the new results, and currently unresolved issues are described.

Topics: Bacteriochlorophylls; Carotenoids; Energy Metabolism; Kinetics; Light-Harvesting Protein Complexes; Photosynthetic Reaction Center Complex Proteins; Rhodobacter sphaeroides; Spectrum Analysis