References of "Franck, Fabrice"
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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 detailLack of isocitrate lyase in Chlamydomonas leads to changes in carbon metabolism and in the response to oxidative stress under mixotrophic growth.
Plancke, Charlotte; Vigeolas, Hélène ULg; Hohner, Ricarda et al

in The Plant journal : for cell and molecular biology (2014), 77(3), 404-417

Isocitrate lyase is a key enzyme of the glyoxylate cycle. This cycle plays an essential role in cell growth on acetate, and is important for gluconeogenesis as it bypasses the two oxidative steps of the ... [more ▼]

Isocitrate lyase is a key enzyme of the glyoxylate cycle. This cycle plays an essential role in cell growth on acetate, and is important for gluconeogenesis as it bypasses the two oxidative steps of the tricarboxylic acid (TCA) cycle in which CO2 is evolved. In this paper, a null icl mutant of the green microalga Chlamydomonas reinhardtii is described. Our data show that isocitrate lyase is required for growth in darkness on acetate (heterotrophic conditions), as well as for efficient growth in the light when acetate is supplied (mixotrophic conditions). Under these latter conditions, reduced acetate assimilation and concomitant reduced respiration occur, and biomass composition analysis reveals an increase in total fatty acid content, including neutral lipids and free fatty acids. Quantitative proteomic analysis by 14 N/15 N labelling was performed, and more than 1600 proteins were identified. These analyses reveal a strong decrease in the amounts of enzymes of the glyoxylate cycle and gluconeogenesis in parallel with a shift of the TCA cycle towards amino acid synthesis, accompanied by an increase in free amino acids. The decrease of the glyoxylate cycle and gluconeogenesis, as well as the decrease in enzymes involved in beta-oxidation of fatty acids in the icl mutant are probably major factors that contribute to remodelling of lipids in the icl mutant. These modifications are probably responsible for the elevation of the response to oxidative stress, with significantly augmented levels and activities of superoxide dismutase and ascorbate peroxidase, and increased resistance to paraquat. [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 detailModelization of photosynthetic and respiratory maximal activities as a function of culture parameters in Chlamydomonas reinhardtii using design of experiment and data analysis by JMP (SAS Institute)
Gerin, Stéphanie ULg; Mathy, Grégory; Franck, Fabrice ULg

Poster (2013, August)

We aimed to modelize the dependence of photosynthetic as well as cytochromial and alternative respiratory maximal activities upon different culture parameters, i.e. light intensity and acetate, carbon ... [more ▼]

We aimed to modelize the dependence of photosynthetic as well as cytochromial and alternative respiratory maximal activities upon different culture parameters, i.e. light intensity and acetate, carbon dioxide, nitrate and ammonium concentrations, in the model unicellular green alga Chlamydomonas reinhardtii. Culture parameters were submitted to a dedicated statistical software (JMP 10.0, SAS Institute) for the generation of a design of experiment. Measurements of oxygen concentrations were carried out to quantify maximal activities. JMP was further used to detect culture parameters exerting a statistically significant effect on maximal activities and to modelize the dependence of maximal activities upon these culture parameters of interest. [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 detailLes microalgues: un défi énergétique
Franck, Fabrice ULg

Conference (2013, June 06)

Les microalgues sont des micro-organismes photosynthétiques dont la culture commerciale en masse est pratiquée depuis les années '60. Les rendements en biomasse de la culture de microalgues sont ... [more ▼]

Les microalgues sont des micro-organismes photosynthétiques dont la culture commerciale en masse est pratiquée depuis les années '60. Les rendements en biomasse de la culture de microalgues sont supérieurs à ceux de cultures traditionnelles, et elle peut s'effectuer sur des terrains impropres à l'agriculture traditionnelle. Les perspectives d'utilisation de la biomasse microalgale pour la production de biocarburants ont suscité d'importants efforts de recherche au cours des années récentes. Les recherches en cours visent à améliorer les souches d'algues utilisables ainsi que différents aspects des procédés de production, de traitement et d'extraction de la biomasse algale afin d'aboutir à moyen terme à un procédé durable et économiquement viable. [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 dual strategy to cope with high light in Chlamydomonas reinhardtii
Allorent, G; Tokutsu, R; Roach, T et al

in Plant Cell (2013), 25(2), 545-557

Absorption of light in excess of the capacity for photosynthetic electron transport is damaging to photosynthetic organisms. Several mechanisms exist to avoid photodamage, which are collectively referred ... [more ▼]

Absorption of light in excess of the capacity for photosynthetic electron transport is damaging to photosynthetic organisms. Several mechanisms exist to avoid photodamage, which are collectively referred to as nonphotochemical quenching. This term comprises at least two major processes. State transitions (qT) represent changes in the relative antenna sizes of photosystems II and I. High energy quenching (qE) is the increased thermal dissipation of light energy triggered by lumen acidification. To investigate the respective roles of qE and qT in photoprotection, a mutant (npq4 stt7-9) was generated in Chlamydomonas reinhardtii by crossing the state transition–deficient mutant (stt7-9) with a strain having a largely reduced qE capacity (npq4). The comparative phenotypic analysis of the wild type, single mutants, and double mutants reveals that both state transitions and qE are induced by high light. Moreover, the double mutant exhibits an increased photosensitivity with respect to the single mutants and the wild type. Therefore, we suggest that besides qE, state transitions also play a photoprotective role during high light acclimation of the cells, most likely by decreasing hydrogen peroxide production. These results are discussed in terms of the relative photoprotective benefit related to thermal dissipation of excess light and/or to the physical displacement of antennas from photosystem II. [less ▲]

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See detailLa photosynthèse: aujourd'hui, hier et demain
Franck, Fabrice ULg

Conference (2012, November 30)

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See detailAlternative photosynthetic electron pathways in symbiotic dinoflagellates of reef-building corals
Roberty, Stéphane ULg; Cardol, Pierre ULg; Franck, Fabrice ULg

Conference (2012, July 11)

The high productivity of coral reef ecosystems is largely attributed to the mutualistic symbiosis between reef-building corals and their intracellular dinoflagellate in the genus Symbiodinium. In the ... [more ▼]

The high productivity of coral reef ecosystems is largely attributed to the mutualistic symbiosis between reef-building corals and their intracellular dinoflagellate in the genus Symbiodinium. In the natural environment the holobiont have to cope with significant daily variations in light intensities that sometimes exceed Symbiodinium photosynthetic capacity. Fortunately, photosynthetic organisms possess regulatory features that help to ensure that high light intensities can be endured without the accumulation of photodamage. Thus, the regulation of photosynthesis can be viewed as a dynamic balance between photosynthetic efficiency (photochemical quenching) and photoprotection processes (i.e. non-photochemical quenching). In addition to the linear electron flow (LEF) operating during oxygenic photosynthesis, alternative electron flows (AEF) have been widely described in higher plants and microalgae but not in Symbiodinium. The present study aimed to highlight the existence of the Mehler ascorbate peroxidase pathway (reduction of oxygen by PSI), chlororespiration (oxidation by molecular O2 of the PQ pool) and cyclic electron flow around PSI. We report that the presence of particular AEF and/or their amplitude vary from one clade to another. These processes could play a key role under particular environmental conditions when sinks for photosynthetic electrons are scarce. Indeed, they could sustain significant levels of photosynthetic electron flux by initiating the ΔpH formation and of NPQ, regulating the ratio of ATP/NADPH to match the requirements of carbon reduction and reducing the excitation pressure over the photosynthetic apparatus. [less ▲]

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See detailOptimization of an Haematococcus pluvialis medium by a Genetic Algorithm-based strategy
Fratamico, Anthony ULg; Tocquin, Pierre ULg; Franck, Fabrice ULg

Poster (2012, June 14)

The successful use of living organisms for the production of biomass or metabolites requires a careful control and optimization over growing conditions. However the range of interacting parameters makes ... [more ▼]

The successful use of living organisms for the production of biomass or metabolites requires a careful control and optimization over growing conditions. However the range of interacting parameters makes full optimization difficult and time-consuming. In this context, Genetic Algorithm-based (GA) methods emerge as promising strategies for optimization of biotechnological processes. However, the potential of GA in the microalgae field remains, today, poorly explored. As a proof-of-concept, we evaluated how GA could be applied for the optimization of a medium for high yield photoautotrophic growth of Haematoccocus pluvialis. [less ▲]

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See detailThe MicroH2 project:an association of four laboratories to improve theknowledge on biohydrogen production precesses
Beckers, Laurent ULg; Calusinska, Magdalena ULg; Hamilton, Christopher ULg et al

Poster (2012, June 04)

This poster presents a collaborative research project (MicroH2) held at the University of Liège (Belgium) since 2007 (www.microh2.ulg.ac.be) and involving four different research groups. The project aims ... [more ▼]

This poster presents a collaborative research project (MicroH2) held at the University of Liège (Belgium) since 2007 (www.microh2.ulg.ac.be) and involving four different research groups. The project aims to develop a center of excellence in the fields of photo- and dark- biohydrogen production. Our studies contribute to improve the knowledge of the processes involved in the microbiological production of hydrogen, from a fundamental and practical point of view. Some results are highlighted here. The research concerning photofermentation focuses on the interactions between respiration, photosynthesis and H2-producing pathways in algal microorganisms, by using mitochondrial mutants and genetically modified strains with modified ability for hydrogen production [1-2]. To study the metabolism of the hydrogen production by anaerobic bacteria, pure cultures and defined consortia are used and their production of biogas and soluble metabolites is measured. Moreover, we have developed and optimized molecular tools, like quantitative RT-PCR and FISH, to monitor the variations of bacterial populations in novel bioreactors for hydrogen production [3-4]. We have also mined the complete genomes of Clostridium spp. for putative hydrogenase genes and found a large diversity of them [5]. [less ▲]

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