Localization of cytochrome b6f complexes implies an incomplete respiratory chain in cytoplasmic membranes of the cyanobacterium Synechocystis sp. PCC 6803

AbstractThe cytochrome b6f complex is an integral part of the photosynthetic and respiratory electron transfer chain of oxygenic photosynthetic bacteria. The core of this complex is composed of four subunits, cytochrome b, cytochrome f, subunit IV and the Rieske protein (PetC). In this study deletion mutants of all three petC genes of Synechocystis sp. PCC 6803 were constructed to investigate their localization, involvement in electron transfer, respiration and photohydrogen evolution. Immunoblots revealed that PetC1, PetC2, and all other core subunits were exclusively localized in the thylakoids, while the third Rieske protein (PetC3) was the only subunit found in the cytoplasmic membrane. Deletion of petC3 and both of the quinol oxidases failed to elicit a change in respiration rate, when compared to the respective oxidase mutant. This supports a different function of PetC3 other than respiratory electron transfer. We conclude that the cytoplasmic membrane of Synechocystis lacks both a cytochrome c oxidase and the cytochrome b6f complex and present a model for the major electron transfer pathways in the two membranes of Synechocystis. In this model there is no proton pumping electron transfer complex in the cytoplasmic membrane.Cyclic electron transfer was impaired in all petC1 mutants. Nonetheless, hydrogenase activity and photohydrogen evolution of all mutants were similar to wild type cells. A reduced linear electron transfer and an increased quinol oxidase activity seem to counteract an increased hydrogen evolution in this case. This adds further support to the close interplay between the cytochrome bd oxidase and the bidirectional hydrogenase

Light distribution and spectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors

[EN] Light, being the fundamental energy source to sustain life on Earth, is the external factor with the strongest impact on photosynthetic microorganisms. Moreover, when considering biotechnological applications such as the production of energy carriers and commodities in photobioreactors, light supply within the reactor volume is one of the main limiting factors for an efficient system. Thus, the prediction of light availability and its spectral distribution is of fundamental importance for the productivity of photo-biological processes. The light field model here presented is able to predict the intensity and spectral distribution of light throughout the reactor volume. The input data for the algorithm are chlorophyll-specific absorption and scattering spectra at different irradiance values for a given organism, the depth of the photobioreactor, the cell-density and also the intensity and emission spectrum of the light source. Although in the form exposed here the model is optimized for photosynthetic microorganism cultures inside flat-type photobioreactors, the theoretical framework is easily extensible to other geometries. Our calculation scheme has been applied to model the light field inside Synechocystis sp. PCC 6803 wild-type and Olive antenna mutant cultures at different cell-density concentrations exposed to LED lamps of different colours, delivering results with reasonable accuracy, despite the data uncertainties. To achieve this, Synechocystis experimental attenuation profiles for different light sources were estimated by means of the Beer- Lambert law, whereby the corresponding downward irradiance attenuation coefficients were obtained through inherent optical properties at any wavelength within the photosynthetically active radiation band. In summary, the model is a general tool to predict light availability inside photosynthetic microorganism cultures and to optimize light supply, in respect to both intensity and spectral distribution, in technological applications. This knowledge is crucial for industrialscale optimisation of light distribution within photobioreactors and a fundamental parameter for unravelling the nature of many photosynthetic processes.This project has received funding from the European Union's Seventh Programme for Research, Technological Development and Demonstration under grant agreement No 308518 CyanoFactory, to Javier Urchueguia's and Matthias Rogner's respective research groups and from the grant Contratos Predoctorales FPI 2013 of the Universitat Politecnica de Valencia to the first one. We would also like to thank David Lea-Smith and Dariusz Stramski for their fruitful and selfless contribution. We kindly acknowledge the experimental support of Saori Fuse for the cultivation of cyanobacteria.Fuente-Herraiz, D.; Keller, J.; Conejero, JA.; Roegner, M.; Rexroth, S.; Urchueguía Schölzel, JF. (2017). Light distribution and spectral composition within cultures of micro-algae: Quantitative modelling of the light field in photobioreactors. Algal Research. 23:166-177. https://doi.org/10.1016/j.algal.2017.01.004S1661772

Metabolism controls dimerization of the chloroplast F0F1 ATP synthase in Chlamydomonas reinhardtii

AbstractDimers and oligomers of F-type ATP synthases have been observed previously in mitochondria of various organisms and for the CFoF1 ATP synthase of chloroplasts of Chlamydomonas reinhardtii. In contrast to mitochondria, however, dimers of chloroplast ATP synthases dissociate at elevated phosphate concentration. This suggests a regulation by cell physiological processes.Stable isotope labeling of living cells and blue-native PAGE have been employed to quantitate changes in the ratio of monomeric to dimeric CFoF1 ATP synthase. Chlamydomonas reinhardtii cells were cultivated photoautotrophically in the presence of 15N and photomixotrophically at natural 14N abundance, respectively.As compared to photoautotrophic growth, an increased assembly of ATP synthase dimers on the expense of preexisting monomers during photomixotrophic growth was observed, demonstrating a metabolic control of the dimerization process

Light-Induced Oxidative Stress, <em>N</em>-Formylkynurenine, and Oxygenic Photosynthesis

<div><p>Light stress in plants results in damage to the water oxidizing reaction center, photosystem II (PSII). Redox signaling, through oxidative modification of amino acid side chains, has been proposed to participate in this process, but the oxidative signals have not yet been identified. Previously, we described an oxidative modification, <em>N</em>-formylkynurenine (NFK), of W365 in the CP43 subunit. The yield of this modification increases under light stress conditions, in parallel with the decrease in oxygen evolving activity. In this work, we show that this modification, NFK365-CP43, is present in thylakoid membranes and may be formed by reactive oxygen species produced at the Mn₄CaO₅ cluster in the oxygen-evolving complex. NFK accumulation correlates with the extent of photoinhibition in PSII and thylakoid membranes. A modest increase in ionic strength inhibits NFK365-CP43 formation, and leads to accumulation of a new, light-induced NFK modification (NFK317) in the D1 polypeptide. Western analysis shows that D1 degradation and oligomerization occur under both sets of conditions. The NFK modifications in CP43 and D1 are found 17 and 14 Angstrom from the Mn₄CaO₅ cluster, respectively. Based on these results, we propose that NFK is an oxidative modification that signals for damage and repair in PSII. The data suggest a two pathway model for light stress responses. These pathways involve differential, specific, oxidative modification of the CP43 or D1 polypeptides.</p> </div

Optical absorption of NFK-containing PSII peptides (A) and the model compounds (B), tryptophan, NFK, and kynurenine.

<p>(A) shows absorption spectra of NFK-containing peptide fractions A–C. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042220#pone.0042220.s002" target="_blank">Table S1</a>, for average retention times from 350 nm chromatograms. Fraction A is displayed as a solid line, fraction B as a dashed line, and fraction C as a dotted line. In (B), absorption spectra of 40 µM tryptophan (solid line), 40 µM NFK (dotted line), and 40 µM kynurenine (dashed line) are shown in water. Absorption spectra in A were derived from the HPLC chromatogram and are on an arbitrary y-scale (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042220#s4" target="_blank">Materials and Methods</a>). The spectra in B were measured on a Hitachi spectrophotometer (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042220#s4" target="_blank">Materials and Methods</a>).</p