References of "Franck, Fabrice"
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See detailNew features on the environmental regulation of metabolism revealed by modeling the cellular proteomic adaptations induced by light, carbon and inorganic nitrogen in Chlamydomonas reinhardtii
Gerin, Stéphanie ULg; Leprince, Pierre ULg; Sluse, Francis ULg et al

in Frontiers in Plant Science (in press)

Microalgae are currently emerging to be very promising organisms for the production of biofuels and high-added value compounds. Understanding the influence of environmental alterations on their metabolism ... [more ▼]

Microalgae are currently emerging to be very promising organisms for the production of biofuels and high-added value compounds. Understanding the influence of environmental alterations on their metabolism is a crucial issue. Light, carbon and nitrogen availability have been reported to induce important metabolic adaptations. So far, the influence of these variables has essentially been studied while varying only one or two environmental factors at the same time. The goal of the present work was to model the cellular proteomic adaptations of the green microalga Chlamydomonas reinhardtii upon the simultaneous changes of light intensity, carbon concentrations (CO2 and acetate) and inorganic nitrogen concentrations (nitrate and ammonium) in the culture medium. Statistical design of experiments (DOE) enabled to define 32 culture conditions to be tested experimentally. Relative protein abundance was quantified by two dimensional differential in-gel electrophoresis (2D-DIGE). Additional assays for respiration, photosynthesis, and lipid and pigment concentrations were also carried out. A hierarchical clustering survey enabled to partition biological variables (proteins + assays) into eight co-regulated clusters. In most cases, the biological variables partitioned in the same cluster had already been reported to participate to common biological functions (acetate assimilation, bioenergetic processes, light harvesting, Calvin cycle and protein metabolism). The environmental regulation within each cluster was further characterized by a series of multivariate methods including principal component analysis and multiple linear regressions. This metadata analysis enabled to highlight the existence of a clear regulatory pattern for every cluster and to mathematically simulate the effects of light, carbon and nitrogen. The influence of these environmental variables on cellular metabolism is described in details and thoroughly discussed. This work provides an overview of the metabolic adaptations contributing to maintain cellular homeostasis upon extensive environmental changes. Some of the results presented here could be used as starting points for more specific fundamental or applied investigations. [less ▲]

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See detailLa production en masse de microalgues: limitations actuelles, perspectives d'amélioration et applications dans le domanaine des pigments valorisables
Franck, Fabrice ULg

Conference (2016, July 06)

Actuellement les productions industrielles de microalgues sont exploitées pour diverses applications commerciales. Les cultures sont le plus souvent réalisées sur le mode photoautotrophe, c’est-à-dire ... [more ▼]

Actuellement les productions industrielles de microalgues sont exploitées pour diverses applications commerciales. Les cultures sont le plus souvent réalisées sur le mode photoautotrophe, c’est-à-dire basées sur l’absorption de lumière pour l’incorporation du carbone du CO2 dans la biomasse. Bien que les productivités atteignent des valeurs respectables par rapport aux rendements agricoles, elles restent limitées par de faibles rendements de conversion de l’énergie solaire, en comparaison avec le rendement théorique maximum. Les raisons généralement évoquées pour expliquer cette limitation sont principalement l’atténuation de la lumière dans les cultures et la saturation de la photosynthèse en surface. Les pistes d’amélioration proposées concernent d’une part la géométrie des systèmes de culture et, d’autre part, l’amélioration génétique des souches de microalgues en vue d’une meilleure efficience énergétique. Des cultures hétérotrophes en fermenteur sont également en développement. Avec les limitations actuelles de productivité, les coûts de production restent élevés pour des applications à faible valeur ajoutée. Les pigments des microalgues, par leur variété et leurs multiples débouchés, représentent une catégorie en expansion de produits économiquement viables. Ils comprennent principalement les caroténoïdes de microalgues vertes et de diatomées, ainsi que les phycobilines des cyanobactéries. [less ▲]

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See detailThe chlorophyll a fluorescence induction curve in the green microalga Haematococcus pluvialis: Further insight into the nature of the P-S-M fluctuation and its relationship with the "low-wave" phenomenon at steady-state
Fratamico, Anthony ULg; Tocquin, Pierre ULg; Franck, Fabrice ULg

in Photosynthesis Research (2016), 128(3), 271-285

Chlorophyll fluorescence is an information-rich signal which provides an access to the management of light absorbed by PSII. A good example of this is the succession of fast fluorescence fluctuations ... [more ▼]

Chlorophyll fluorescence is an information-rich signal which provides an access to the management of light absorbed by PSII. A good example of this is the succession of fast fluorescence fluctuations during light-induced photosynthetic induction after dark-adaptation. During this period, the fluorescence trace exhibits several inflexion points: O-J-I-P-S-M-T. Thereas the OJIP part of this kinetics has been the subject of many studies, the processes that underly the PSMT transient are less understood. Here, we report an analysis of the PSMT phase in the green microalga Haematococcus pluvialis in terms of electron acceptors and light use by photochemistry, fluorescence and non-photochemical quenching (NPQ). We identify additional sub-phases between P and S delimited by an inflexion point, that we name Q, found in the second time-scale. The P-Q phase expresses a transient photochemical quenching specifically due to alternative electron transport to oxygen. During the transition from Q to S, the NPQ increases and then relaxes during the S-M phase in about 1 min. It is suggested that this transient NPQ observed during induction is a high energy state quenching (qE) dependent the alternative electron transport to molecular oxygen. We further show that this NPQ is of the same nature than the NPQ, known as the low-wave phenomenon, which is transiently observed after a saturating light pulse given at steady-state. In both cases, the NPQ is oxygen-dependent. This NPQ is observed at external pH 6.0, but not at pH 7.5, which seems correlated with faster saturation of the PQ pool at pH 6.0. [less ▲]

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See detailBiotechnologies algales: état actuel et perspectives de valorisation de la biomasse
Franck, Fabrice ULg

Scientific conference (2016, May 12)

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See detailLa culture industrielle de microalgues
Franck, Fabrice ULg

Conference given outside the academic context (2016)

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See detailCritical role of oxygen photoreduction downstream of PSI in Symbiodinium: photoprotection, energetic adjustement and ROS production
Roberty, Stéphane ULg; Bailleul, Benjamin; Berne, Nicolas ULg et al

Conference (2015, August)

The ecological success of symbiotic cnidarians (reef building-corals and sea anemones) relies on the symbiosis between cnidarians and photosynthetic dinoflagellates of the genus Symbiodinium ... [more ▼]

The ecological success of symbiotic cnidarians (reef building-corals and sea anemones) relies on the symbiosis between cnidarians and photosynthetic dinoflagellates of the genus Symbiodinium. Photosynthetic organisms have evolved various photoprotective and regulatory mechanisms to cope with changing and high light intensities, but the nature and relative amplitude of these mechanisms is still a matter of debate in Symbiodinium. Few studies showed that molecular oxygen (O2) can be an efficient electron sink during photosynthesis in Symbiodinium, with an O2 uptake capacity that could represent up to half the maximum O2 evolution. In addition, members of clade A Symbiodinium were proposed to possess enhanced capabilities for alternative photosynthetic electron flows. In this work, the amplitude of photosynthetic alternative electron flows to oxygen (chlororespiration, Mehler reaction, mitochondrial respiration) and PSI cyclic electron flow were investigated in Symbiodinium strains belonging to different Clades (A, B and F). Joint measurements of oxygen evolution, PSI and PSII activities allowed us to demonstrate that photoreduction of oxygen downstream PSI by the so-called Mehler reaction is the main alternative electron sink at the onset and steady state of photosynthesis in all strains1. This mechanism in Symbiodinium sustains significant photosynthetic electron flux under high light, thus acting as a photoprotective mechanism and modifying the ratio of ATP/NADPH to match the requirements of carbon reduction. At higher temperature (26 to 33°C), the amplitude of Mehler reaction was still significantly increased but the capacity of enzymes responsible for superoxide detoxification largely decreased. This imbalance generated twice more ROS than during the treatment at 26°C, suggesting that under conditions known to induce coral bleaching, the photoprotective role of Mehler reaction can no longer be maintained, at least at short term. [less ▲]

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See detailLa culture industrielle de microalgues
Franck, Fabrice ULg

Conference given outside the academic context (2015)

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See detailImbalance between oxygen photoreduction and antioxidant capacities in Symbiodinium cells exposed to combined heat and high light stress
Roberty, Stéphane ULg; Fransolet, David; Cardol, Pierre ULg et al

in Coral Reefs (2015), 34

During last decades coral reefs have been affected by several large-scale bleaching events and such phenomenon is expected to increase in frequency and severity in the future thus compromising their ... [more ▼]

During last decades coral reefs have been affected by several large-scale bleaching events and such phenomenon is expected to increase in frequency and severity in the future thus compromising their survival. High sea surface temperature accompanied by high levels of solar irradiance has been found to be responsible for the induction of an oxidative stress ultimately ending with the disruption of the symbiosis between cnidarians and Symbiodinium. Since two decades many studies have pointed out the water-water cycle as being one of the primary mediators of this phenomenon, but the impacts of environmental stress on the O2 reduction by PSI and the associated ROS-detoxifying enzymes remain to be determined. In this study, we analyzed the impacts of an acute thermal and light stress on the WWC in the model Symbiodinium strain A1. We observed that high light treatment at 26°C resulted in the up-regulation of superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR) activities and an increased production of Reactive Oxygen Species (ROS) with no significant change in O2-dependent electron transport. Under high light and at 33°C, O2-dependent electron transport was significantly increased relative to total electron transport. This increase was concomitant with a two-fold increase in ROS generation compared to the treatment at 26°C, while enzymes involved in the WWC were largely inactivated. These data show for the first time that combined heat and light stress inactivate antioxidant capacities of the WWC, and suggests that its photoprotective functions are overwhelmed under these conditions. This study also indicates that cnidarians may be more prone to bleach if they harbor Symbiodinium cells having a highly active Mehler-type electron transport, unless they are able to quickly up-regulate their antioxidant capacities. [less ▲]

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See detailGenome-wide transcriptional analysis suggests hydrogenase- and nitrogenase-mediated hydrogen production in Clostridium butyricum CWBI 1009
Calusinska, Magda; Hamilton, Christopher; Monsieurs, Pieter et al

in Biotechnology for Biofuels (2015), 8(27), 1-16

Background: Molecular hydrogen, given its pollution-free combustion, has great potential to replace fossil fuels in future transportation and energy production. However, current industrial hydrogen ... [more ▼]

Background: Molecular hydrogen, given its pollution-free combustion, has great potential to replace fossil fuels in future transportation and energy production. However, current industrial hydrogen production processes, such as steam reforming of methane, contribute significantly to the greenhouse effect. Therefore alternative methods, in particular the use of fermentative microorganisms, have attracted scientific interest in recent years. However the low overall yield obtained is a major challenge in biological H2 production. Thus, a thorough and detailed understanding of the relationships between genome content, gene expression patterns, pathway utilisation and metabolite synthesis is required to optimise the yield of biohydrogen production pathways. Results: In this study transcriptomic and proteomic analyses of the hydrogen-producing bacterium Clostridium butyricum CWBI 1009 were carried out to provide a biomolecular overview of the changes that occur when the metabolism shifts to H2 production. The growth, H2-production, and glucose-fermentation profiles were monitored in 20 L batch bioreactors under unregulated-pH and fixed-pH conditions (pH 7.3 and 5.2). Conspicuous differences were observed in the bioreactor performances and cellular metabolisms for all the tested metabolites, and they were pH dependent. During unregulated-pH glucose fermentation increased H2 production was associated with concurrent strong up-regulation of the nitrogenase coding genes. However, no such concurrent up-regulation of the [FeFe] hydrogenase genes was observed. During the fixed pH 5.2 fermentation, by contrast, the expression levels for the [FeFe] hydrogenase coding genes were higher than during the unregulated-pH fermentation, while the nitrogenase transcripts were less abundant. The overall results suggest, for the first time, that environmental factors may determine whether H2 production in C. butyricum CWBI 1009 is mediated by the hydrogenases and/or the nitrogenase. Conclusions: This work, contributing to the field of dark fermentative hydrogen production, provides a multidisciplinary approach for the investigation of the processes involved in the molecular H2 metabolism of clostridia. In addition, it lays the groundwork for further optimisation of biohydrogen production pathways based on genetic engineering techniques. [less ▲]

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See detailPSI Mehler reaction is the main alternative photosynthetic electron pathway in Symbiodinium sp., symbiotic dinoflagellates of cnidarians
Roberty, Stéphane ULg; Bailleul, Benjamin ULg; Berne, Nicolas et al

in New Phytologist (2014), 204(1), 81-91

• Photosynthetic organisms have evolved various photoprotective and regulatory mechanisms to cope with changing and high light intensities. The nature and relative amplitude of these mechanisms is matter ... [more ▼]

• Photosynthetic organisms have evolved various photoprotective and regulatory mechanisms to cope with changing and high light intensities. The nature and relative amplitude of these mechanisms is matter of debate in dinoflagellates that live in symbiosis with cnidarians. In this work, the amplitude of photosynthetic alternative electron flows to oxygen (chlororespiration, Mehler reaction, mitochondrial respiration) and PSI cyclic electron flow were investigated in Symbiodinium clades A1, B1 and F1. • Cultured Symbiodinium strains were maintained semi-continuously under identical environmental conditions. Joint measurements of oxygen evolution, fluorescence emission, and absorption changes at specific wavelengths were used to evaluate PSI and PSII electron transfer rates (ETR). • A light-dependent and O2-dependent ETR was observed in all strains. This ETR involved PSII and PSI and was insensitive to addition of mitochondrial and carbon fixation inhibitors. • These results demonstrate that photoreduction of oxygen downstream of PSI by the so-called Mehler reaction is the main alternative electron sink at the onset and steady state of photosynthesis in all strains. This mechanism in Symbiodinium sustains significant levels of photosynthetic electron flux under high light, thus acting as a photoprotective mechanism and increasing the ATP/NADPH ratio by the electron transfer chain. [less ▲]

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See detailLiver proteomic response to hypertriglyceridemia in human-apolipoprotein C-III transgenic mice at cellular and mitochondrial compartment levels
Ehx, Grégory ULg; Gerin, Stéphanie ULg; Mathy, Grégory et al

in Lipids in Health and Disease (2014), 13

Background: Hypertriglyceridemia (HTG) is defined as a triglyceride (TG) plasma level exceeding 150 mg/dl and is tightly associated with atherosclerosis, metabolic syndrome, obesity, diabetes and acute ... [more ▼]

Background: Hypertriglyceridemia (HTG) is defined as a triglyceride (TG) plasma level exceeding 150 mg/dl and is tightly associated with atherosclerosis, metabolic syndrome, obesity, diabetes and acute pancreatitis. The present study was undertaken to investigate the impact of hypertriglyceridemia on the mitochondrial, sub-mitochondrial and cellular proteomes in the hepatocytes of a hypertriglyceridemic transgenic mouse model overexpressing the human apolipoproteinC-III. Methods: Quantitative comparative proteomics (2D-DIGE) was carried out in both “low-expressor” (LE) and “high-expressor” (HE) mice, respectively exhibiting moderate and severe HTG, to characterize the effect of the TG plasma level on the proteomic response. Results: The mitoproteome analysis revealed the occurrence of a large-scale adaptation in transgenic mice consisting of a general down-regulation of matricial proteins and up-regulation of inner membrane proteins. Remarkably, the magnitude of these proteomic changes appears to strongly depend on the TG plasma level. Altogether, our different analyses indicate that, in HE mice, the capacity of several metabolic pathways is altered to promote the availability of acetyl-CoA, glycerol-3-phosphate, ATP and NADPH for de novo TG biosynthesis. The up-regulation of several cytosolic ROS detoxifying enzymes also tend to confirm that the cytoplasm of HTG mice is subjected to oxidative stress as previously stated. The up-regulation of cytosolic ferritin indicates that iron over-accumulation could take place in the cytosol of HE mice hepatocytes and contribute to (i) enhance oxidative stress and (ii) promote cellular proliferation. Conclusions: The present analyses demonstrate that important TG dose-responsive metabolic adaptations are set up in human apolipoproteinC-III-overexpressing mice. Our results indicate that these adaptations could support the higher TG production rates which have been previously reported in this HTG model, and also suggest that cytosolic oxidative stress may result from FFA over-accumulation, iron overload and enhanced activity of some ROS-producing catabolic enzymes. [less ▲]

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See detailApplications des microalgues
Franck, Fabrice ULg; Remacle, Claire ULg

Conference (2014, May 22)

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See detailCumulative effect of Aox1 inactivation and N source modulation on the cellular proteome of Chlamydomonas reinhardtii - New insights in the metabolic interconnexion between respiration and photosynthesis
Gerin, Stéphanie ULg; Mathy, Grégory; Franck, Fabrice ULg

Conference (2014, April 14)

In Chlamydomonas reinhardtii, the Aox1 gene encoding the mitochondrial alternative oxidase (AOX) is tightly regulated by the N source: its transcription is stimulated by nitrate and repressed by ammonium ... [more ▼]

In Chlamydomonas reinhardtii, the Aox1 gene encoding the mitochondrial alternative oxidase (AOX) is tightly regulated by the N source: its transcription is stimulated by nitrate and repressed by ammonium. AOX has been proposed to play a key role in regards to the N source by acting as a trigger factor for the TCA cycle to promote the production of reduced cofactors which, together with photo-generated reductant, could contribute to support nitrate assimilation. In the present work, the cellular proteomes of wild-type and AOX-deficient strains grown either on nitrate or ammonium in the presence of acetate have been compared using two dimensional-differential in-gel electrophoresis (2D-DIGE) coupled to hierarchical clustering and ANOVA-2 statistical analyses in order to further investigate the physiological role(s) of AOX, particularly in regards to the N source. The dramatic up-regulation of chloroplastic components of the carbon-concentrating mechanism (CCM) in response to Aox1 inactivation importantly suggests that AOX plays a key role in the CCM in both N sources by allowing the production of CO2 through the TCA cycle. The concomitant down-regulation of photorespiratory enzymes in cells lacking AOX indicates that such an induction of the CCM could actually be sufficient to over-compensate the effects of AOX deficiency on CO2 availability in the local environment of Rubisco and maintain high rates of inorganic carbon fixation despite lower TCA cycle-mediated CO2 production. The global overexpression of diverse photosynthetic chain and Calvin cycle components in cells lacking AOX further evidences that a tight functional relationship exists between mitochondrial and chloroplastic processes of energy transduction, and that there could be a global redirection of bioenergetics towards photosynthesis to limit the harmful consequences (particularly oxidative stress) of mitochondrial deficiency. The observation that numerous N-responsive proteomic modifications are strongly attenuated (or even abolished) in response to Aox1 inactivation supports that AOX also exerts a more specific role as a central effector of the metabolic plasticity induced by modulating the N source in the growth medium. Our proteomic results tend notably to confirm that respiration (through AOX activity) and photosynthesis collaborate to provide nitrate reduction with electrons in mixotrophic condition and that acetate oxidation could be promoted to support AOX involvement in this context. [less ▲]

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See detailStudy of an undershoot in chlorophyll fluorescence signal after a saturating pulse in PAM measurements
Fratamico, Anthony ULg; Cardol, Pierre ULg; Tocquin, Pierre ULg et al

Conference (2014, April 14)

In 1989, Larcher and Neuner have reported the observation of a sudden reversible drop in modulated chlorophyll fluorescence measurements (PAM) immediately after a saturating pulse, and called it “low ... [more ▼]

In 1989, Larcher and Neuner have reported the observation of a sudden reversible drop in modulated chlorophyll fluorescence measurements (PAM) immediately after a saturating pulse, and called it “low-wave”. 25 years later, whereas some papers reported this phenomenon as a trivial detail, scarcely two works have investigated the origin of this particular signal, in which a link with a low CO2 availability seems clear. Our work on Haematococcus pluvialis, a freshwater green microalga, provides a new point of view on this fluorescence undershoot, caused by a rapidly established non-photochemical quenching. We have demonstrated that in the light-adapted state, a low-wave after a saturating flash can be considered as a consequence of an induction process engaged in response to the brief light increase under low CO2 conditions. The non-photochemical quenching during low-waves was found to be dependent on electron transport to oxygen during the preceding flash. Moreover, in conditions in which low-waves were observed in the light-adapted state, the fluorescence induction kinetics in the first minute of lighting after dark-adaptation presented also a reversible strong drop. Nevertheless, at the stationary state, oxygen production and photochemical yield of photosystem II were not affected. Providing a better understanding of the processes underlying low-waves, our work also draws attention on the effect of CO2 concentration on the onset of photosynthesis. [less ▲]

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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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