References of "Alric, Jean"
     in
Bookmark and Share    
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 47 (18 ULg)
Full Text
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 ▲]

Detailed reference viewed: 57 (17 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 8 (4 ULg)
Full Text
Peer Reviewed
See detailImpaired respiration discloses the physiological significance of state transitions in Chlamydomonas.
Cardol, Pierre ULg; Alric, Jean; Girard-Bascou, Jacqueline et al

in Proceedings of the National Academy of Sciences of the United States of America (2009), 106(37), 15979-84

State transitions correspond to a major regulation process for photosynthesis, whereby chlorophyll protein complexes responsible for light harvesting migrate between photosystem II and photosystem I in ... [more ▼]

State transitions correspond to a major regulation process for photosynthesis, whereby chlorophyll protein complexes responsible for light harvesting migrate between photosystem II and photosystem I in response to changes in the redox poise of the intersystem electron carriers. Here we disclose their physiological significance in Chlamydomonas reinhardtii using a genetic approach. Using single and double mutants defective for state transitions and/or mitochondrial respiration, we show that photosynthetic growth, and therefore biomass production, critically depends on state transitions in respiratory-defective conditions. When extra ATP cannot be provided by respiration, enhanced photosystem I turnover elicited by transition to state 2 is required for photosynthetic activity. Concomitant impairment of state transitions and respiration decreases the overall yield of photosynthesis, ultimately leading to reduced fitness. We thus provide experimental evidence that the combined energetic contributions of state transitions and respiration are required for efficient carbon assimilation in this alga. [less ▲]

Detailed reference viewed: 37 (10 ULg)