References of "Franck, Fabrice"
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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 detailCycle écologique de Dunaliella salina et Artemia salina en relation avec la fluctuation des paramètres physicochimiques des eaux de la saline Sebkhet Al Hdhibet au sud tunisien
Ammar, Jihenne; Ben Ouada, Hatem; Franck, Fabrice ULg et al

in Mésogée (2013), 69

Le présent travail s’intéresse à la variation saisonnière des caractéristiques biologiques et physicochimiques des eaux de la saline de Sebkhat Al Hdhibet au sud tunisien. Des mesures biologiques (densité ... [more ▼]

Le présent travail s’intéresse à la variation saisonnière des caractéristiques biologiques et physicochimiques des eaux de la saline de Sebkhat Al Hdhibet au sud tunisien. Des mesures biologiques (densité cellulaire en Dunaliella et Artemia), physiques et chimiques ont été effectuées sur plusieurs zones du site et à différentes périodes de l’année. L’interaction entre tous ces paramètres a été évaluée, dans l’espace et dans le temps, moyennant la méthode multidimensionnelle de l’analyse factorielle en composantes principales (ACP). Les résultats montrent que ce milieu hyperhalin favorise la poussée exclusive de deux micro- organismes halophiles : Dunaliella salina et Artemia salina, et permettent de tracer le cycle écologique annuel de ces deux espèces. Les plus fortes concentrations en A. salina sont enregistrées en fin d’hiver et début du printemps lorsque les pluies diluent les sels du milieu et diminuent le pH, favorisant l’augmentation des taux de bicarbonates. En fin de printemps, D. salina atteint sa concentration maximale. En été, lorsque la température des eaux dépasse 30°C, la salinité augmente, provoquant la précipitation progressive de sels et la réduction des taux de bicarbonates dans le milieu. A l’exception des puits de pompages, qui représentent une réserve en Dunaliella, la saline se dessèche dans sa majeure partie. 24% de cellules de D. salina sont piégés dans les cristaux de sels. Les cultures réalisées au laboratoire à partir de ces cristaux montrent que ces cellules reprennent rapidement leur croissance avec des vitesses avoisinant 100 000 cellules/ml/j, en pleine phase exponentielle. [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 detailMetabolic plasticity of wild-type and AOX-deficient Chlamydomonas reinhardtii cells related to the inorganic nitrogen source (nitrate or ammonium), as revealed by a 2D-DIGE comparative proteomic analysis
Gerin, Stéphanie ULg; Mathy, Grégory; Franck, Fabrice ULg

Poster (2012, June 15)

In the model unicellular green alga Chlamydomonas reinhardtii, both nitrate and ammonium can be used as primary inorganic nitrogen sources. Interestingly, the expression of the mitochondrial alternative ... [more ▼]

In the model unicellular green alga Chlamydomonas reinhardtii, both nitrate and ammonium can be used as primary inorganic nitrogen sources. Interestingly, the expression of the mitochondrial alternative oxidase (AOX), an "energy-dissipating" ubiquinol-oxygen oxidoreductase of the mitochondrial electron transport chain, is under the control of the exogenous nitrogen source : it is activated in nitrate-grown cells and repressed in ammonium-grown cells at both transcriptional and translational levels. This regulation of AOX by nitrogen is Chlamydomonas-specific and currently its bioenergetic and metabolic significance is poorly understood. In order to get clues to this peculiar phenomenon, we characterized the global metabolic response of a wild-type strain (WT) and an AOX-deficient mutant (AOX-) obtained by RNA interference grown either on nitrate or ammonium. For this purpose, we used a highly accurate 2D electrophoresis-based comparative proteomic approach (2D-DIGE) to compare the cellular proteomes of nitrate and ammonium-grown WT and AOX- Chlamydomonas. The analysis was performed in the middle of the exponential growth phase in mixotrophic conditions. It revealed many proteomic modifications between WT and AOX- cells and a smaller number between nitrate and ammonium-grown cells. In nitrate-grown cells, we notably observed an important up-regulation of glutamine synthetase. Interestingly, in AOX- cells, we respectively detected a general down-regulation and a general up-regulation of mitochondrial and chloroplastic bioenergetic enzymes, and also an important up-regulation of glutathione-dependent oxidative stress defense systems together with a remarkable down-regulation of methionine synthase. Altogether these results and previous studies provide new features in understanding the metabolic adaptations occurring in response to the inorganic nitrogen source with emphasis on the role played by AOX. [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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See detailRegulation of the pigment optical density of an algal cell: filling the gap between photosynthetic productivity in the laboratory and in mass culture
Formighieri, Cinzia; Franck, Fabrice ULg; Bassi, Roberto

in Journal of Biotechnology (2012), 162

An increasing number of investors is looking at algae as a viable source of biofuels, beside Q3 cultivation for human/animal feeding or to extract high-value chemicals and pharmaceuticals. However ... [more ▼]

An increasing number of investors is looking at algae as a viable source of biofuels, beside Q3 cultivation for human/animal feeding or to extract high-value chemicals and pharmaceuticals. However, present biomass productivities are far below theoretical estimations implying that a large part of the available photosynthetically active radiation is not used in photosynthesis. Light utilisation inefficiency and rapid light attenuation within a mass culture due to high pigment optical density of wild type strains have been proposed as major limiting factors reducing solar-to-biomass conversion efficiency. Analysis of growth yields of mutants with reduced light-harvesting antennae and/or reduced overall pigment concentration per cell, generated by either mutagenesis or genetic engineering, could help understanding limiting factors for biomass accumulation in photobioreactor. Meanwhile, studies on photo-acclimation can provide additional information on the average status of algal cells in a photobioreactor to be used in modellingbased predictions. Identifying limiting factors in solar-to-biomass conversion efficiency is the first step for planning strategies of genetic improvement and domestication of algae to finally fill the gap between theoretical and industrial photosynthetic productivity. [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 detailFinding the bottleneck: a research strategy for improved biomass production
Bassi, Roberto; Cardol, Pierre ULg; Choquet, Yves et al

in Posten, Clemens; Walter, Christian (Eds.) Microalgal Biotechnology: integration and economy (2012)

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See detailUne brève histoire des centres réactionnels de la photosynthèse
Franck, Fabrice ULg

in Bulletin de la Société Royale des Sciences de Liège (2012), 81

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See detailScreening for a low-cost Haematococcus pluvialis medium reveals an unexpected impact of a low N:P ratio on vegetative growth
Tocquin, Pierre ULg; Fratamico, Anthony ULg; Franck, Fabrice ULg

in Journal of Applied Phycology (2012), 24(3), 365-373

Haematococcus pluvialis is the current better source of natural astaxanthin, a high-value carotenoid. Traditionally, the production process of astaxanthin by this algae is achieved by a two-stage system ... [more ▼]

Haematococcus pluvialis is the current better source of natural astaxanthin, a high-value carotenoid. Traditionally, the production process of astaxanthin by this algae is achieved by a two-stage system: during the first stage, vegetative “green” cells are produced and then converted, in the second stage, into cysts that accumulate astaxanthin. In this work, a medium screening strategy based on the mixing of a 3-component hydroponic fertilizer was applied to identify a new formulation optimized for the vegetative stage. A maximal and high cell density of 2 x 106 cells mL−1 was obtained in a medium containing a high level of phosphate relative to nitrate, resulting in a N:P ratio much lower than commonly used media for H. pluvialis. In this medium, cells remained at the vegetative and motile stage during a prolonged period of time. Both high cell density culture and motile stage persistence was proved to be related to the N:P feature of this medium. We conclude that the macrozoid stage of H. pluvialis is favored under high-P and low-N supply and that low-cost hydroponic fertilizers can be successfully used for achieving high density cultures of vegetative cells of H. pluvialis. [less ▲]

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