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Lavaud, Johann

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Lavaud

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Johann

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Université Laval. Département de biologie

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ncf11887044

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Voici les éléments 1 - 5 sur 5
  • PublicationAccès libre
    Potential for the production of carotenoids of interest in the polar diatom Fragilariopsis cylindrus
    (Basel : MDPI, 2022-07-29) Guérin, Sébastien; Raguénès, Laura; Croteau, Dany; Lavaud, Johann; Babin, Marcel
    Carotenoid xanthophyll pigments are receiving growing interest in various industrial fields due to their broad and diverse bioactive and health beneficial properties. Fucoxanthin (Fx) and the inter-convertible couple diadinoxanthin–diatoxanthin (Ddx+Dtx) are acknowledged as some of the most promising xanthophylls; they are mainly synthesized by diatoms (Bacillariophyta). While temperate strains of diatoms have been widely investigated, recent years showed a growing interest in using polar strains, which are better adapted to the natural growth conditions of Nordic countries. The aim of the present study was to explore the potential of the polar diatom Fragilariopsis cylindrus in producing Fx and Ddx+Dtx by means of the manipulation of the growth light climate (daylength, light intensity and spectrum) and temperature. We further compared its best capacity to the strongest xanthophyll production levels reported for temperate counterparts grown under comparable conditions. In our hands, the best growing conditions for F. cylindrus were a semicontinuous growth at 7 °C and under a 12 h light:12 h dark photoperiod of monochromatic blue light (445 nm) at a PUR of 11.7 µmol photons m⁻² s⁻¹. This allowed the highest Fx productivity of 43.80 µg L⁻¹ day⁻¹ and the highest Fx yield of 7.53 µg Wh⁻¹, more than two times higher than under "white" light. For Ddx+Dtx, the highest productivity (4.55 µg L⁻¹ day⁻¹) was reached under the same conditions of "white light" and at 0 °C. Our results show that F. cylindrus, and potentially other polar diatom strains, are very well suited for Fx and Ddx+Dtx production under conditions of low temperature and light intensity, reaching similar productivity levels as model temperate counterparts such as Phaeodactylum tricornutum. The present work supports the possibility of using polar diatoms as an efficient cold and low light-adapted bioresource for xanthophyll pigments, especially usable in Nordic countries.
  • PublicationAccès libre
    Green Edge ice camp campaigns : understanding the processes controlling the under-ice Arctic phytoplankton spring bloom
    (Göttingen Copernicus Publications, 2020-01-27) Massicotte, Philippe; Amiraux, Rémi; Amyot, Marie-Pier; Archambault, Philippe; Aubry, Cyril; Ayotte, Pierre; Bécu, Guislain; Bélanger, Simon; Bruyant, Flavienne; Christiansen-Stowe, Debra; Coupel, Pierre; Dezutter, Thibaud; Dominé, Florent; Dufour, Francis; Dufresne, Christiane; Dumont, Dany; Ferland, Joannie; Forget, Marie-Hélène; Fortier, Louis; Galí, Martí; Galindo, Virginie; Gourdal, Margaux; Grondin, Pierre-Luc; Guillot, Pascal; Guilmette, Caroline; Lacour, Léo; Lagunas, José Luis; Lalande, Catherine; Laliberté, Julien; Lambert Girard, Simon; Larivière, Jade; Lavaud, Johann; LeBaron, Anita; Lemire, Mélanie; Levasseur, Maurice; Marec, Claudie; Massé, Guillaume; Matsuoka, Atsushi; Neukermans, Griet; Oziel, Laurent; Rehm, Eric Carl; Reimer, Erin; Saint-Béat, Blanche; Sansoulet, Julie; Tremblay, Jean-Éric; Verin, Gauthier; Babin, Marcel
    The Green Edge initiative was developed to investigate the processes controlling the primary productivity and fate of organic matter produced during the Arctic phytoplankton spring bloom (PSB) and to determine its role in the ecosystem. Two field campaigns were conducted in 2015 and 2016 at an ice camp located on landfast sea ice southeast of Qikiqtarjuaq Island in Baffin Bay (67.4797∘ N, 63.7895∘ W). During both expeditions, a large suite of physical, chemical and biological variables was measured beneath a consolidated sea-ice cover from the surface to the bottom (at 360 m depth) to better understand the factors driving the PSB. Key variables, such as conservative temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured at the ice camp. Meteorological and snow-relevant variables were also monitored. Here, we present the results of a joint effort to tidy and standardize the collected datasets, which will facilitate their reuse in other Arctic studies.
  • PublicationAccès libre
    Contrasting nonphotochemical quenching patterns under high light and darkness aligns with light niche occupancy in Arctic diatoms
    (Wiley Online Library, 2020-09-02) Ferland, Joannie; Guérin, Sébastien; Croteau, Dany; Babin, Marcel; Bruyant, Flavienne; Campbell, Douglas A.; Lavaud, Johann
    Over the seasons, Arctic diatom species occupy shifting habitats defined by contrasting light climates, constrained by snow and ice cover dynamics interacting with extreme photoperiod and solar angle variations. How Arctic diatom photoadaptation strategies differ across their heterogeneous light niches remains a poorly documented but crucial missing link to anticipate Arctic Ocean responses to shrinking sea-ice and increasing light. To address this question, we selected five Arctic diatom species with diverse life traits, representative of distinct light niches across the seasonal light environment continuum: from snow-covered dimly lit bottom ice to summer stratified waters. We studied their photoacclimation plasticity to two growth light levels and the subsequent responses of their nonphotochemical quenching (NPQ) and xanthophyll cycle to both dark incubations and light shifts. We deciphered NPQ and xanthophyll cycle tuning in darkness and their light-dependent induction kinetics, which aligned with species' light niche occupancy. In ice-related species, NPQ was sustained in darkness and its induction was more reactive to moderate light shifts. Open-water species triggered strong NPQ induction in darkness and reached higher maximal NPQ under high light. Marginal ice zone species showed strong adaptation to light fluctuations with a dark response fine-tuned depending upon light history. We argue these traits are anchored in diverging photoadaption strategies fostering Arctic diatom success in their respective light niches.
  • PublicationAccès libre
    Genome-scale metabolic reconstruction and in silico perturbation analysis of the polar diatom fragilariopsis cylindrus predicts high metabolic robustness
    (2020-02-17) Saint-Béat, Blanche; Strauss, Jan; Allard, Antoine; Guérin, Sébastien; Hardy, Simon; Lavaud, Johann; Falciatore, Angela; Lavoie, Michel
    Diatoms are major primary producers in polar environments where they can actively grow under extremely variable conditions. Integrative modeling using a genome-scale model (GSM) is a powerful approach to decipher the complex interactions between components of diatom metabolism and can provide insights into metabolic mechanisms underlying their evolutionary success in polar ecosystems. We developed the first GSM for a polar diatom, Fragilariopsis cylindrus, which enabled us to study its metabolic robustness using sensitivity analysis. We find that the predicted growth rate was robust to changes in all model parameters (i.e., cell biochemical composition) except the carbon uptake rate. Constraints on total cellular carbon buffer the effect of changes in the input parameters on reaction fluxes and growth rate. We also show that single reaction deletion of 20% to 32% of active (nonzero flux) reactions and single gene deletion of 44% to 55% of genes associated with active reactions affected the growth rate, as well as the production fluxes of total protein, lipid, carbohydrate, DNA, RNA, and pigments by less than 1%, which was due to the activation of compensatory reactions (e.g., analogous enzymes and alternative pathways) with more highly connected metabolites involved in the reactions that were robust to deletion. Interestingly, including highly divergent alleles unique for F. cylindrus increased its metabolic robustness to cellular perturbations even more. Overall, our results underscore the high robustness of metabolism in F. cylindrus, a feature that likely helps to maintain cell homeostasis under polar conditions.
  • PublicationAccès libre
    Shifts in growth light optima among diatom species support their succession during the spring bloom in the Arctic
    (Cambridge : John Wiley & Sons Ltd, 2022-03-01) Lafond, Augustin; Croteau, Dany; Campbell, Douglas A. (Douglas Andrew),; Lacour, Thomas; Schiffrine, Nicolas; Morin, Philippe-Israël; Forget, Marie-Hélène; Bruyant, Flavienne; Ferland, Joannie; Tremblay, Jean-Éric; Lavaud, Johann; Babin, Marcel
    1. Diatoms of the Arctic Ocean annually experience extreme changes of light environment linked to photoperiodic cycles and seasonal variations of the snow and sea‐ice cover extent and thickness which attenuate light penetration in the water column. Arctic diatom communities exploit this complex seasonal dynamic through a well‐documented species succession during spring, beginning in sea‐ice and culminating in massive phytoplankton blooms underneath sea‐ice and in the marginal ice zone. The pattern of diatom taxa sequentially dominating this succession is relatively well conserved interannually, and taxonomic shifts seem to align with habitat transitions. 2. To understand whether differential photoadaptation strategies among diatom taxa explain these recurring succession sequences, we coupled lab experiments with field work in Baffin Bay at 67.5°N. Based on field data, we selected five diatom species typical of different ecological niches and measured their growth rates under light intensity ranges representative of their natural habitats. To characterize their photoacclimative responses, we sampled pigments and total particulate carbon, and conducted 14C‐uptake photosynthesis response curves and variable fluorescence measurements. 3. We documented a gradient in species respective light intensity for maximal growth suggesting divergent light response plasticity, which for the most part align with species sequential dominance. Other photophysiological parameters supported this ecophysiological framing, although contrasts were always clear only between succession endmembers, Nitzschia frigida and Chaetoceros neogracilis. To validate that these photoacclimative responses are representative of in situ dynamics, we compared them to the chlorophyll a‐specific light‐limited slope (α*) and saturated rate of photosynthesis (P*M), monitored in Baffin Bay on sea‐ice and planktonic communities. This complementary approach confirmed that unusual responses in α* and P*M as a function of light history intensity are similar between sentinel sympagic species N. frigida and natural ice‐core communities. While no light‐history‐dependent trends were observed in planktonic communities, their α* and P*M values were in the range of measurements from our monospecific cultures. 4. Synthesis. Our results suggest that Arctic diatoms species photoadaptation strategy is tuned to the light environment of the habitats in which they dominate and indeed drives the seasonal taxonomic succession.