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See detailAnalysis of PSII antenna size heterogeneity of Chlamydomonas reinhardtii during state transitions
de Marchin, Thomas ULg; Ghysels, Bart ULg; Nicolay, Samuel ULg et al

in Biochimica et Biophysica Acta-Bioenergetics (2014), 1837(1), 121-130

PSII antenna size heterogeneity has been intensively studied in the past. Based on DCMU fluorescence rise kinetics, multiple types of photosystems with different properties were described. However, due to ... [more ▼]

PSII antenna size heterogeneity has been intensively studied in the past. Based on DCMU fluorescence rise kinetics, multiple types of photosystems with different properties were described. However, due to the complexity of fluorescence signal analysis, multiple questions remain unanswered. The number of different types of PSII is still debated as well as their degree of connectivity. In Chlamydomonas reinhardtii we found that PSIIα possesses a high degree of connectivity and an antenna 2-3 times larger than PSIIβ, as described previously. We also found some connectivity for PSIIβ in contrast with the majority of previous studies. This is in agreement with biochemical studies which describe PSII mega-, super- and core- complexes in Chlamydomonas. In these studies, the smallest unit of PSII in vivo would be a dimer of two core complexes hence allowing connectivity. We discuss the possible relationships between PSIIα and PSIIβ and the PSII mega-, super- and core- complexes. We also showed that strain and medium dependent variations in the half-time of the fluorescence rise can be explained by variations in the proportions of PSIIα and PSIIβ. When analyzing the state transition process in vivo, we found that this process induces an inter-conversion of PSIIα and PSIIβ. During a transition from state 2 to state 1, DCMU fluorescence rise kinetics are satisfactorily fitted by considering two PSII populations with constant kinetic parameters. We discuss our findings about PSII heterogeneity during state transitions in relation with recent results on the remodeling of the pigment-protein PSII architecture during this process. [less ▲]

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See detailStudy of photosynthesis of Chlamydomonas reinhardtii under High and Low CO2 conditions.
de Marchin, Thomas ULg; Ghysels, Bart ULg; Franck, Fabrice ULg

Poster (2013, August 12)

In photoautotophically air-grown microalgae, CO2 availability is usually limited. The unicellular green algae Chlamydomonas reinhardtii can adapt to low CO2 concentration with the inorganic carbon ... [more ▼]

In photoautotophically air-grown microalgae, CO2 availability is usually limited. The unicellular green algae Chlamydomonas reinhardtii can adapt to low CO2 concentration with the inorganic carbon concentration mechanism (CCM). This has been extensively studied in the past but functional adaptation of the photosynthetic apparatus has been less studied. Photosynthetic organisms can cope with CO2 limitation by dissipating excess absorbed energy with the help of different energy dissipating mechanisms like energy-dependent non-photochemical quenching (NPQ). In Chlamydomonas reinhardtii, this process only seems to develop to high levels in extreme conditions combining high light and strong CO2 limitation. Under moderate CO2 limitation, absence of important energy-dependent NPQ suggests the development of another energy dissipating mechanism. We compared the growth and functional adaptations of the photosynthetic apparatus of the wild-type strain 1690 grown in photobioreactor under low and high CO2 bubbling, 0.039% and 10%, respectively. Under low CO2, where growth was 2 to 4 times slower than under high CO2, the non-linear relationship between electron transport rate (derived from PAM fluorescence measurements) and gross oxygen evolution rate suggested that a significant portion of the electron flux is directed to oxygen at light intensities approaching photosynthetic saturation (either at PSI or at PTOX). The use of the mutant strain PTOX2 indicated that O2 reduction occurs mainly at PSI and not at PTOX. Low temperature fluorescence emission spectra indicated no significant difference in excitation energy distribution between PSI and PSII. Western blot analysis showed no major differences in abundance of Rubisco or of photosystem subunits between the two conditions. In contrast, cytochrome f abundance was lower in high CO2 condition. Although energy-dependent NPQ remained weak, low CO2 cells were characterized by a higher xanthophyll deepoxydation index which usually indicates more dissipation as heat, as also suggested by increased Lhcsr3 expression. Despite a higher ATP requirement of the CCM mechanism in low CO2 condition, only minor difference in cyclic electron transport could be found if compared to high CO2 condition (as determined by P700 spectroscopic measurements). In Chlamydomonas, conflicting views were expressed in earlier studies on the amplitude and role of Mehler-type O2-uptake at steady state. Our analysis of oxygen evolution, electron transport and NPQ after growth under different combinations of light intensities and CO2 supply rates allows us to define Mehler-type alternative electron transport as an important and flexible response to photosynthetic electron transport saturation in Chlamydomonas. [less ▲]

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See detailAnalysis of PSII antenna size heterogeneity of Chlamydomonas reinhardtii during state transitions - Colloque annuel de la Société Française de Photosynthèse
de Marchin, Thomas ULg; Ghysels, Bart ULg; Nicolay, Samuel ULg et al

Conference (2013, June 18)

PSII antenna size heterogeneity has been extensively studied in the past. Based on in vivo DCMU fluorescence rise kinetics, at least two types of photosystems were described. They differ by their apparent ... [more ▼]

PSII antenna size heterogeneity has been extensively studied in the past. Based on in vivo DCMU fluorescence rise kinetics, at least two types of photosystems were described. They differ by their apparent antenna size and connectivity (this last term refers to the transfer of absorbed energy from a closed PSII unit to an open neighboring unit). In this study, we analysed PSII heterogeneity in Chlamydomonas reinhardtii using non-linear linear regression fitting on in vivo DCMU fluorescence rise kinetics, with a focus on changes in PSII heterogeneity associated with state transitions. We found that PSIIα possesses a high degree of connectivity and an antenna about 3 times larger than PSIIβ, as described previously. In contrast with most earlier studies, we found some connectivity for PSIIβ (although it was highly variable). This is in agreement with recent models based on biochemical and structural analysis of PSII after gel filtration separation which describe PSII mega-, super- and core- complexes in Chlamydomonas. According to these studies, the smallest unit of PSII in vivo would be a dimer of two core complexes hence still allowing connectivity. We also showed that strain and medium dependent variations in the half-time of the fluorescence rise, generally taken as an indicator of the average cross-section of PSII, can be explained by variations in the proportions of PSIIα and PSIIβ. When analyzing the state transition process, we showed for the first time in vivo that it induces an inter-conversion of PSIIα and PSIIβ. These findings are discussed with respect to the latest insights on the remodeling of the pigment-protein PSII architecture during this process. [less ▲]

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See detailFunction of the Chloroplast Hydrogenase in the Microalga Chlamydomonas: The Role of Hydrogenase and State Transitions during Photosynthetic Activation in Anaerobiosis
Ghysels, Bart ULg; Godaux, Damien ULg; Matagne, René-Fernand ULg et al

in PLoS ONE (2013), 8(5), 64161

Like a majority of photosynthetic microorganisms, the green unicellular alga Chlamydomonas reinhardtii may encounter O2 deprived conditions on a regular basis. In response to anaerobiosis or in a ... [more ▼]

Like a majority of photosynthetic microorganisms, the green unicellular alga Chlamydomonas reinhardtii may encounter O2 deprived conditions on a regular basis. In response to anaerobiosis or in a respiration defective context, the photosynthetic electron transport chain of Chlamydomonas is remodeled by a state transition process to a conformation that favours the photoproduction of ATP at the expense of reductant synthesis. In some unicellular green algae including Chlamydomonas, anoxia also triggers the induction of a chloroplast-located, oxygen sensitive hydrogenase, which accepts electrons from reduced ferredoxin to convert protons into molecular hydrogen. Although microalgal hydrogen evolution has received much interest for its biotechnological potential, its physiological role remains unclear. By using specific Chlamydomonas mutants, we demonstrate that the state transition ability and the hydrogenase function are both critical for induction of photosynthesis in anoxia. These two processes are thus important for survival of the cells when they are transiently placed in an anaerobic environment. [less ▲]

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See detailA novel screening method for hydrogenase-deficient mutants in Chlamydomonas reinhardtii based on in vivo chlorophyll fluorescence and photosystem II quantum yield
Godaux, Damien ULg; Emonds-Alt, Barbara ULg; Berne, Nicolas ULg et al

in International Journal of Hydrogen Energy (2013), 38

In Chlamydomonas reinhardtii, prolonged anaerobiosis leads to the expression of enzymes <br />Received 30 August 2012 belonging to various fermentative pathways. Among them, oxygen-sensitive hydrogenases ... [more ▼]

In Chlamydomonas reinhardtii, prolonged anaerobiosis leads to the expression of enzymes <br />Received 30 August 2012 belonging to various fermentative pathways. Among them, oxygen-sensitive hydrogenases <br />Received in revised form (HydA1/2) catalyze the synthesis of molecular hydrogen from protons and reduced ferre- <br />12 November 2012 doxin in the stroma. In this work, by analyzing wild type and mutants affected in H2 <br />Accepted 16 November 2012 production, we show that maximal PSII photosynthetic electron transfer during the first <br />Available online 21 December 2012 seconds of illumination after a prolonged dark-anaerobiosis period is linearly related to <br />hydrogenase capacity. Based on the specific chlorophyll fluorescence induction kinetics <br />Keywords: typical of hydrogenase-deficient mutants, we set up an in vivo fluorescence imaging <br />Chlamydomonas reinhardtii screening protocol allowing to isolate mutants impaired in hydrogenase expression or <br />Anaerobic photosynthesis activity, as well as mutants altered in related metabolic pathways required for energy <br />Hydrogenase production in anaerobiosis. Compared to previously described screens for mutants <br />Chlorophyll fluorescence impaired in H2 production, our screening method is remarkably fast, sensitive and non- <br />Microalgae invasive. Out of 3000 clones from a small-sized insertional mutant library, five mutants <br />Hydrogen photoproduction were isolated and the most affected one was analyzed and shown to be defective for the <br />hydrogenase HydG assembly factor. [less ▲]

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See detailLight induced photosynthetic electron transfer upon anaerobiosis in Chlamydomonas: Kinetics, electron sinks and setup of a fluorescence screen to identify new players
Godaux, Damien ULg; Emonds-Alt, Barbara ULg; Alric, Jean et al

Conference (2012, June 15)

In Chlamydomonas reinhardtii, prolonged anaerobiosis leads to the expression of various fermentative pathways. Among them, oxygen-sensitive hydrogenases (hyd) catalyze the reduction of protons from ... [more ▼]

In Chlamydomonas reinhardtii, prolonged anaerobiosis leads to the expression of various fermentative pathways. Among them, oxygen-sensitive hydrogenases (hyd) catalyze the reduction of protons from reduced ferredoxin resulting in the production of molecular hydrogen. In this work, light-induced photosynthetic electron transfer after a prolonged dark-anaerobiosis period was studied by following the kinetics of chlorophyll fluorescence emission, P700 oxidation and proton-motive force formation and consumption during the first 3 seconds of illumination. We show that during the induction of photosynthesis, an hyd-dependent photosynthetic electron transfer operates at a maximal rate of 110 electrons per photosystem per second, that is about half the one measured in aerobiosis. The implication in this process of components of the linear, cyclic and chlororespiratory electron transfer pathways, as well as various electron sinks, are investigated thanks to the availability of mutants. In a next step, we screen an insertional mutant library (~3000 clones) on the basis of the fluorescence induction kinetics upon a shift from dark-anaerobiosis to light. Five mutants display the signature of mutants deficient for NADPH:PQ oxidoreductase or hyd activities. In particular, one is defective for hydrogenase HydG assembly factor. This mutant behaves exactly has the hydEF mutant, thus confirming that in vivo both the assembly factors are required for an efficient hydrogenase activity. [less ▲]

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See detailFunction of the chloroplastic NAD(P)H dehydrogenase Nda2 for H(2) photoproduction in sulphur-deprived Chlamydomonas reinhardtii.
Mignolet, Emmanuel; Lecler, Renaud; Ghysels, Bart ULg et al

in Journal of biotechnology (2012), 162(1), 81-8

The relative contributions of the PSII-dependent and Nda2-dependent pathways for H(2) photoproduction were investigated in the green microalga Chlamydomonas reinhardtii after suphur-deprivation. For this ... [more ▼]

The relative contributions of the PSII-dependent and Nda2-dependent pathways for H(2) photoproduction were investigated in the green microalga Chlamydomonas reinhardtii after suphur-deprivation. For this purpose, H(2) gas production was compared for wild-type and Nda2-deficient cells with or without DCMU (a PSII-inhibitor) in the same experimental conditions. Nda2-deficiency caused a 30% decrease of the maximal H(2) photoevolution rate observed shortly after the establishment of anoxia, and an acceleration of the decline of H(2) photoevolution rate with time. DCMU addition to Nda2-deficient cells completely inhibited H(2) photoproduction, showing that the PSII-independent H(2) photoproduction relies on the presence of Nda2, which feeds the photosynthetic electron transport chain with electrons derived from oxidative catabolism. Nda2-protein abundance increased as a result of sulphur deprivation and further during the H(2) photoproduction process, resulting in high rates of non-photochemical plastoquinone reduction in control cells. Nda2-deficiency had no significant effect on photosynthetic and respiratory capacities in sulphur-deprived cells, but caused changes in the cell energetic status (ATP and NADPH/NADP+ ratio). The rapid decline of H(2) photoevolution rate with time in Nda2-deficient cells revealed a more pronounced inhibition of H(2) photoproduction by accumulated H(2) in the absence of non-photochemical plastoquinone reduction. Nda2 is therefore important for linking H(2) photoproduction with catabolism of storage carbon compounds, and seems also involved in regulating the redox poise of the photosynthetic electron transport chain during H(2) photoproduction. [less ▲]

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See detailFunction of the chloroplastic NADP(H) dehydrogenase NDA2 for the H2 photoproduction in sulphur-deprived Chlamydomonas reinhardtii
Mignolet, Emmanuel ULg; Lecler, Renaud ULg; Ghysels, Bart ULg et al

in Journal of Biotechnology (2012), 162

The relative contributions of the PSII-dependent and Nda2-dependent pathways for H2 photoproduction were investigated in the green microalga Chlamydomonas reinhardtii after suphur-deprivation. For this ... [more ▼]

The relative contributions of the PSII-dependent and Nda2-dependent pathways for H2 photoproduction were investigated in the green microalga Chlamydomonas reinhardtii after suphur-deprivation. For this purpose, H2 gas production was compared for wild-type and Nda2-deficient cells with or without DCMU (a PSII-inhibitor) in the same experimental conditions. Nda2-deficiency caused a 30 % decrease of the maximal H2 photoevolution rate observed shortly after the establishment of anoxia, and an acceleration of the decline of H2 photoevolution rate with time. DCMU addition to Nda2-deficient cells completely inhibited H2 photoproduction, showing that the PSII-independent H2 photoproduction relies on the presence of Nda2, which feeds the photosynthetic electron transport chain with electrons derived from oxidative catabolism. Nda2-protein abundance increased as a result of sulphur deprivation and further during the H2 photoproduction process, resulting in high rates of non-photochemical plastoquinone reduction in control cells. Nda2-deficiency had no significant effect on photosynthetic and respiratory capacities in sulphur-deprived cells, but caused changes in the cell energetic status (ATP and NADPH/NADP+ ratio). The rapid decline of H2 photoevolution rate with time in Nda2-deficient cells revealed a more pronounced inhibition of H2 photoproduction by accumulated H2 in the absence of non-photochemical plastoquinone reduction. Nda2 is therefore important for linking H2 photoproduction with catabolism of storage carbon compounds, and seems also involved in regulating the redox poise of the photosynthetic electron transport chain during H2 photoproduction. [less ▲]

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See detailInterplay between non-photochemical plastoquinone reduction and re-oxidation in pre-illuminated Chlamydomonas reinhardtii: a chlorophyll fluorescence study
Houyoux, Pierre-Alain; Ghysels, Bart ULg; Lecler, Renaud ULg et al

in Photosynthesis Research (2011), 110

In photosynthetic eukaryotes, the redox state of the plastoquinone (PQ) pool is an important sensor for mechanisms that regulate the photosynthetic electron transport. In higher plants, a multimeric ... [more ▼]

In photosynthetic eukaryotes, the redox state of the plastoquinone (PQ) pool is an important sensor for mechanisms that regulate the photosynthetic electron transport. In higher plants, a multimeric nicotinamide adenine dinucleotide (phosphate) (NAD(P))H dehydroge- nase (NDH) complex and a plastid terminal oxidase (PTOX) are involved in PQ redox homeostasis in the dark. We recently demonstrated that in the microalgae Chla- mydomonas reinhardtii, which lacks the multimeric NDH complex of higher plants, non-photochemical PQ reduction is mediated by a monomeric type-II NDH (Nda2). In this study, we further explore the nature and the importance of non-photochemical PQ reduction and oxidation in relation to redox homeostasis in this alga by recording the ‘dark’ chlorophyll fluorescence transients of pre-illuminated algal samples. From the observation that this fluorescence tran- sient is modified by addition of propyl gallate, a known inhibitor of PTOX, and in a Nda2-deficient strain we conclude that it reflects post-illumination changes in the redox state of PQ resulting from simultaneous PTOX and Nda2 activity. We show that the post-illumination fluo- rescence transient can be used to monitor changes in the relative rates of the non-photochemical PQ reduction and reoxidation in response to different physiological situa- tions. We study this fluorescence transient in algae acclimated to high light and in a mutant deficient in mitochondrial respiration. Some of our observations indi- cate that the chlororespiratory pathway participates in redox homeostasis in C. reinhardtii. [less ▲]

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See detailA Chlamydomonas mutant locked in anaerobiosis
Ghysels, Bart ULg; Matagne, René-Fernand ULg; Franck, Fabrice ULg

Conference (2011, May)

The soil dwelling microalga Chlamydomonas reinhardtii most likely encounters transient periods of anaerobiosis in its natural environment, for instance at night time or when photosynthesis is turned down ... [more ▼]

The soil dwelling microalga Chlamydomonas reinhardtii most likely encounters transient periods of anaerobiosis in its natural environment, for instance at night time or when photosynthesis is turned down in response to macronutrient limitation. Anoxic conditions trigger state I to state II transition in C.r. and the induction of a chloroplast hydrogenase., which ability to accept electrons from reduced Fd results in a transient light driven H2 evolution. We present evidence that hydrogenase induction and state transitions are required for the induction of photosynthesis in anaerobiosis and therefore critical for this alga in order to survive transient anaerobic periods in the dark. In an anaerobic metabolic context the induction of photosynthesis is severely slowed down. The highly reduced state of the NAD(P) pools and the absence of O2 as electron sink hamper light driven reoxydation of the intersystem electron carriers while CO2 assimilation by the Calvin cycle is inhibited by ATP deficiency. We have seen that gradual increase of hydrogenase activity during anaerobiosis restores a PSI acceptor pool and leads to a reduction of the induction lag of oxygenic photosynthesis. A mutant HydEF devoid of hydrogenase maturation genes typically shows 3 to 4 times longer lag phases that the WT. State transitions provide another mechanism by which photosynthetic electron transport can be unlocked in anaerobic conditions. A state II conformation is known to stimulate photo-phosphorylation, and may therefore restore Calvin cycle activity in an ATP depleted metabolic context. We observed that an anaerobically adapted stt7 mutant locked in state I is only able to induce oxygenic photosynthesis upon hydrogenase expression. We therefore constructed a double mutant Stt7HydEF impaired of state transition ability and hydrogenase activity and found it to have lost the capacity of inducing photosynthesis in anaerobic conditions. [less ▲]

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See detailControl of hydrogen photoproduction by the proton gradient generated by cyclic electron flow in Chlamydomonas reinhardtii.
Tolleter, Dimitri; Ghysels, Bart ULg; Alric, Jean et al

in Plant Cell (2011), 23(7), 2619-30

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H(2) production is a transitory ... [more ▼]

Hydrogen photoproduction by eukaryotic microalgae results from a connection between the photosynthetic electron transport chain and a plastidial hydrogenase. Algal H(2) production is a transitory phenomenon under most natural conditions, often viewed as a safety valve protecting the photosynthetic electron transport chain from overreduction. From the colony screening of an insertion mutant library of the unicellular green alga Chlamydomonas reinhardtii based on the analysis of dark-light chlorophyll fluorescence transients, we isolated a mutant impaired in cyclic electron flow around photosystem I (CEF) due to a defect in the Proton Gradient Regulation Like1 (PGRL1) protein. Under aerobiosis, nonphotochemical quenching of fluorescence (NPQ) is strongly decreased in pgrl1. Under anaerobiosis, H(2) photoproduction is strongly enhanced in the pgrl1 mutant, both during short-term and long-term measurements (in conditions of sulfur deprivation). Based on the light dependence of NPQ and hydrogen production, as well as on the enhanced hydrogen production observed in the wild-type strain in the presence of the uncoupling agent carbonyl cyanide p-trifluoromethoxyphenylhydrazone, we conclude that the proton gradient generated by CEF provokes a strong inhibition of electron supply to the hydrogenase in the wild-type strain, which is released in the pgrl1 mutant. Regulation of the trans-thylakoidal proton gradient by monitoring pgrl1 expression opens new perspectives toward reprogramming the cellular metabolism of microalgae for enhanced H(2) production. [less ▲]

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See detailLa réponse photosynthétique d'une algue verte à la carence en soufre
de Marchin, Thomas ULg; Ghysels, Bart ULg; Franck, Fabrice ULg

Book published by Editions universitaires europeennes (2010)

Chlamydomonas reinhardtii possède la capacité de produire de l'hydrogène à la lumière en absence d'oxygène. Cette condition peut être obtenue en cultivant les algues dans un milieu carencé en soufre. La ... [more ▼]

Chlamydomonas reinhardtii possède la capacité de produire de l'hydrogène à la lumière en absence d'oxygène. Cette condition peut être obtenue en cultivant les algues dans un milieu carencé en soufre. La carence en soufre entraîne une forte diminution de l'activité du photosystème II tout en maintenant une respiration élevée, ce qui provoque un passage de cultures fermées en anoxie et induit la production d'hydrogène. Dans cette étude, nous avons caractérisé la réponse photosynthétique à la carence en soufre chez la souche sauvage et la souche déficiente en oxydase alternative mictochondriale (AOX) dans des milieux contenant de l'ammonium ou du nitrate comme source d'azote. L'AOX, inductible par le nitrate, fait partie de la chaîne de transport d'électrons mitochondriale et catalyse l'oxydation de l'ubiquinol en transférant directement ses électrons à l'oxygène. Ainsi l'AOX entre en compétition avec le complexe III et est impliquée dans une voie de dissipation du pouvoir réducteur en excès. [less ▲]

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See detailProteomic and functional characterization of a Chlamydomonas reinhardtii mutant lacking the mitochondrial alternative oxidase 1
Mathy, Grégory ULg; Cardol, Pierre ULg; Dinant, Monique et al

in Journal of Proteome Research (2010), 9

In the present work we have isolated by RNA interference and characterized at the functional and the proteomic levels a Chlamydomonas reinhardtii strain devoid of the mitochondrial alternative oxidase ... [more ▼]

In the present work we have isolated by RNA interference and characterized at the functional and the proteomic levels a Chlamydomonas reinhardtii strain devoid of the mitochondrial alternative oxidase (AOX). The AOX-deficient strain displays a doubling of the cell volume and biomass without any alteration of the generation time, a significantly higher ROS production, no change in total respiration rate, and a slight decrease of the photosynthesis efficiency. In order to identify the molecular adaptation underlying these phenotypical effects, we carried out a comparative proteomic study at the level of the mitochondrial and cellular soluble proteomes. Our results indicate a strong up-regulation of the ROS scavenging systems and important modifications of proteins involved in the primary metabolism, namely an increase of enzymes involved in anabolic pathways and a concomitant general down-regulation of enzymes of the main catabolic pathways. [less ▲]

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See detailHydrogen photo-evolution upon S deprivation stepwise: An illustration of microalgal photosynthetic and metabolic flexibility and a step stone for future biotechnological methods of renewable H2 production
Ghysels, Bart ULg; Franck, Fabrice ULg

in Photosynthesis Research (2010), 106

The metabolic flexibility of some photosynthetic microalgae enables them to survive periods of anaerobiosis in the light by developing a particular photofermentative metabolism. The latter entails ... [more ▼]

The metabolic flexibility of some photosynthetic microalgae enables them to survive periods of anaerobiosis in the light by developing a particular photofermentative metabolism. The latter entails compounds of the photosynthetic electron transfer chain and an oxygen-sensitive hydrogenase in order to reoxidise reducing equivalents and to generate ATP for maintaining basal metabolic function. This pathway results in the photo-evolution of hydrogen gas by the algae. A decade ago Melis and coworkers managed to reproduce such a condition in a laboratory context by depletion of sulfur in the algal culture media, making the photo-evolution by the algae sustainable for several days (Melis et al. 2000). This observation boosted research in algal H2 evolution. A feature, which due to its transient nature was long time considered as a curiosity of algal photosynthesis suddenly became a phenomenon with biotechnological potential. Although the Melis procedure has not been developed into a biotechnological process of renewable H2 generation so far, it has been a useful tool for studying microalgal metabolic and photosynthetic flexibility and a possible step stone for future H2 production procedures. Ten years later most of the critical steps and limitations of H2 production by this protocol have been studied from different angles particularly with the model organism C. reinhardtii, by introducing various changes in culture conditions and making use of mutants issued from different screens or by reverse genomic approaches. A synthesis of these observations with the most important conclusions driven from recent studies will be presented in this review. [less ▲]

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See detailDistribution and evolution of ferripyoverdine receptors in Pseudomonas aeruginosa.
Bodilis, Josselin; Ghysels, Bart ULg; Osayande, Julie et al

in Environmental microbiology (2009), 11(8), 2123-35

Pseudomonas aeruginosa is a ubiquitous gram-negative bacterium, which is also able to cause severe opportunistic infections in humans. The colonization of the host is importantly affected by the ... [more ▼]

Pseudomonas aeruginosa is a ubiquitous gram-negative bacterium, which is also able to cause severe opportunistic infections in humans. The colonization of the host is importantly affected by the production of the high-affinity iron (III) scavenging peptidic siderophore pyoverdine. The species P. aeruginosa can be divided into three subgroups ('siderovars'), each characterized by the production of a specific pyoverdine and receptor (FpvA). We used a multiplex PCR to determine the FpvA siderovar on 345 P. aeruginosa strains from environmental or clinical origin. We found about the same proportion of each type in clinical strains, while FpvA type I was slightly over-represented (49%) in environmental strains. Our multiplex PCR also detected the presence or absence of an additional receptor for type I pyoverdine (FpvB). The fpvB gene was in fact present in the vast majority of P. aeruginosa strains (93%), regardless of their siderovar or their origin. Finally, molecular analyses of fpvA and fpvB genes highlighted a complex evolutionary history, probably linked to the central role of iron acquisition in the ecology and virulence of P. aeruginosa. [less ▲]

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