Do photosynthetic cells communicate with each other during cell death? From cyanobacteria to vascular plants

As in metazoans, life in oxygenic photosynthetic organisms relies on the accurate regulation of cell death. During development and in response to the environment, photosynthetic cells activate and execute cell death pathways that culminate in the death of a specific group of cells, a process known as regulated cell death (RCD). RCD control is instrumental, as its misregulation can lead to growth penalties and even the death of the entire organism. Intracellular molecules released during cell demise may act as ‘survival’ or ‘death’ signals and control the propagation of cell death to surrounding cells, even in unicellular organisms. This review explores different signals involved in cell-cell communication and systemic signalling in photosynthetic organisms, in particular Ca2+, reactive oxygen species, lipid derivates, nitric oxide, and eATP. We discuss their possible mode-of-action as either ‘survival’ or ‘death’ molecules and their potential role in determining cell fate in neighbouring cells. By comparing the knowledge available across the taxonomic spectrum of this coherent phylogenetic group, from cyanobacteria to vascular plants, we aim at contributing to the identification of conserved mechanisms that control cell death propagation in oxygenic photosynthetic organisms.Fil: Aguilera, Anabella. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Distefano, Ayelen Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; ArgentinaFil: Jauzein, Cécile. No especifíca;Fil: Correa Aragunde, Maria Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Biológicas. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Biológicas; ArgentinaFil: Martinez, Dana Ethel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Martin, María Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; ArgentinaFil: Sueldo, Daniela Jorgelina. Norwegian University of Science and Technology; Norueg

Changes in community assemblages during the development of a thin layer of phytoplankton (TLP)

ASLO 2021 Aquatic Sciences Meeting, 22–27 June, VirtualHigh resolution measurements of phytoplankton (from pico- to mesoplankton) and physicochemical parameters were made from 2 to 14 July, 2018 in a coastal embayment (Ría de Pontevedra, NW Spain). The main objective of this work was to study changes in phytoplankton community structure during the development of a phytoplankton thin layer. The observational approach highlighted the role of short term changes of abiotic and biotic habitat conditions in the dynamics of phytoplankton assemblages. During relaxation conditions in the beginning of the cruise, small rounded dinoWagellates Alexandrium minutum (PSP toxins) and Scrippsiella cf. dominated. Then, during the transition from downwelling to upwelling conditions, a thin layer was formed, composed of Pseudo-Nitzschia spp (ASP toxins) and Leptocylindrus danicus. Fine spatial (cm-m) and temporal (hours-days) scale measurements were carried out. A combination of traditional microscopy analysis (279 samples analyzed at species level when possible) and imaging-in-Wow technique for morphometric characterization (280 samples generating about 480000 raw images, containing plankton, detritus and mineral particles) allowed us to assess the effect of the environmental =ltering on phytoplankton morphological and functional traits. The dynamics of co-occurring populations of Pseudo-nitzschia spp and Alexandrium minutum was considered in the frame of changing habitat conditionsThis study was funded by project REMEDIOS (CTM2016-75451-C2-2-R).N

Basin scale variability of Ostreopsis spp. blooms provides evidence of effectiveness of an integrated sampling approach

Special issue Marine Benthic Harmful Algal Blooms.-- 12 pages, 8 figures, 5 tables.-- Data availability: Data will be made available on requestOstreopsis spp. blooms have been occurring in the last two decades in the Mediterranean Sea in association with a variety of biotic and abiotic substrata (macroalgae, seagrasses, benthic invertebrates, sand, pebbles and rocks). Cells proliferate attached to the surfaces through mucilaginous trichocysts, which lump together microalgal cells, and can also be found in the plankton and on floating aggregates: such tychoplanktonic behavior makes the quantitative assessment of blooms more difficult than planktonic or benthic ones. Different techniques have been so far applied for quantifying cell abundances of benthic microalgae for research, monitoring and risk assessment purposes. In this context, the Benthic Dinoflagellates Integrator (BEDI), a non-destructive quantification method for benthic dinoflagellate abundances, was developed and tested within the EU ENPI-CBCMED project M3-HABs. This device allows mechanical detachment of cells without collecting the benthic substrate, providing an integrated assessment of both epiphytic and planktonic cells, i.e. of the number of cells potentially made available in the water volume from “resuspension” which could have harmful effects on other organisms (including humans). The present study confirms the effectiveness of the BEDI sampling device across different environments across the Mediterranean Sea and constitutes the first large-scale study of Ostreopsis spp. blooms magnitude in function of different macro- and meso‑habitat features across the basinThis publication has been produced with the financial assistance of the European Union under the ENPI CBC Mediterranean Sea Basin Programme, within the project M3-HABs, and the project OstreoRisk (CTM2014–53818-R) of the Spanish Government (MINECO) and the “Severo Ochoa Centre of Excellence” Accreditation under Grant CEX2019–000928-SPeer reviewe

Etude et paramétrisation de la nutrition azotée et phosphorée d Alexandrium catenella, microalgue toxique responsable d efflorescences dans la lagune de Thau

L'activité ostréicole de l'Etang de Thau subit, depuis une dizaine d'années, des pertes de production régulières dues à des contaminations des parcs conchylicoles par des microalgues toxiques de l'espèce Alexandrium catenella. Cette thèse a été menée dans le but d'améliorer la compréhension des processus de contrôle environnementaux régulant ces efflorescences toxiques, en étudiant plus particulièrement l'influence des éléments nutritifs azotés et phosphorés sur la croissance d'A. catenella. Ces travaux ont permis de mettre en évidence une grande variété de sources potentielles nutritives pour cette espèce, dont la majorité peut être régénérée au niveau de la colonne d'eau. Différentes sources organiques contribueraient à la croissance d'A. catenella grâce à divers processus de nutrition : absorption direct à travers la membrane plasmique (pour l'urée), dégradation enzymatique dans le milieu extracellulaire (pour le phosphore organique dissous) ou phagocytose (pour internaliser des cyanobactéries). Ces capacités mixotrophes représenteraient un des avantages compétitif permettant à cette espèce de réaliser des efflorescences de grande ampleur ; un autre correspondrait à l'utilisation potentielle de nutriments azotés la nuit. Les expérimentations réalisées ont de plus révélé une grande complexité dans les processus de nutrition de cette espèce, par la mise en évidence de variations temporelles dans les capacités d'absorption, de phénomènes d'excrétion/réabsorption et d'interactions entre processus d'assimilation. Cette complexité a pu être en partie paramétrée afin de définir des relations mathématiques pouvant être intégrées à un futur modèle de croissanceIn the Thau lagoon, blooms of the toxic microalgae Alexandrium catenella have induced regular losses of shellfish production since 1998 due to bioaccumulation of toxins in oysters and mussels. This thesis was conducted to enhance knowledge of toxic bloom development regulation by environmental factors, focusing on nitrogen and phosphorus nutrients influence on A. catenella growth. These works highlighted a large variety of potential nutritive sources for this species and a major part of these nutrients appeared to be potentially regenerated in the water column. Different organic sources may contribute to the growth of A. catenella from diverse nutrition processes: direct absorption through the cell membrane (for urea), enzymatic degradation in the extracellular medium (for dissolved organic phosphorus) or phagocytosis (for ingestion of cyanobacteria). These mixotrophic capacities may represent competitive advantages for this species allowing the development of huge blooms; another competitive advantage may correspond to the potential use of nitrogen nutrients at night. A high complexity in nutrition processes of this species was revealed through observation of temporal variations in uptake capacities, excretion/absorption phenomena and interactions between nutrient uptake processes. The parametrization of a part of this complexity allowed the definition of mathematical formulations which can be integrated in a future growth modelMONTPELLIER-BU Sciences (341722106) / SudocPLOUZANE-Bibl.La Pérouse (290195209) / SudocSudocFranceF

Interactions between ammonium and urea uptake by five strains of Alexandrium catenella (Dinophyceae) in culture

10 pages, 3 figures, 2 tablesShort-term experiments were carried out to investigate whether interactions between ammonium (NH4+) and urea uptake regulate the total nitrogen assimilation of the toxic dinoflagellate Alexandrium catenella. To test for strain variability, 5 strains of A. catenellafrom the NW Mediterranean were used: 3 strains from the Thau lagoon (southern France) and 2 strains from the Catalonia basin (Spain). For each strain, the uptake rate of 1 nutrient (NH4+or urea) at a reference concentration (10 μgatN l–1) was measured as a function of the increasing concentration of the other nutrient (0to 10 μgatN l–1). Simultaneous N uptake rates of the distinct nitrogen sources were obtained from 15 N-NH4+ and 15N-urea incorporation measurements. A strong inhibition of urea uptake by NH4+ (maximum inhibition, Imax> 55%) was observed exclusively for the French strains. No influence of urea on the NH4+-uptake rate was noted for any strain. Estimation of total N uptake rates revealed that the N-urea uptake inhibition was not a competitive disadvantage for A. catenellacells considering that the reduced N-urea uptake was more than compensated for by NH4+uptake. Furthermore, the computation of composite kinetic parameters from total N uptake data suggested that French strains were more competitive than the Spanish ones in an environment characterized by low NH4+ concentrations (≤5 μgatN l–1) and high urea concentrations (as 10 μgatN l–1). These N uptake characteristics may reflect particular metabolic adaptations by the strains to their respective environment.We thank R. Ventosa for the nutrient analyses. This study was financed by the Centre National de la Recherche Scientifique (CNRS) and Institut Français pour l’Exploitation de la Mer (Ifremer) ALTOX program, as well as the EU-funded Research Project SEED (Life cycle transformations among HAB species, and the environmental and physiological factors that regulate them, GOCE-CT 2005-003875). S.L. was supported by a Fundação para a Ciência e para a Tecnologia, Portugal (FCT) grant within the III Quadro Comunitário de Apoio by the Fundo Social Europeu. E.G. was supported by the Ramon y Cajal contract of the Spanish Ministry of Education and Science. C.J. was supported by a scholarship from the Région Languedoc-Roussillon and IfremPeer reviewe

Environmental control and dynamics of blooms of the benthic toxic dinoflagellate Ostreopsis cf. ovata in the Mediterranean Sea

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Short-term temporal variability of ammonium and urea uptake by Alexandrium Catenella (Dinophyta) in cultures

10 pages, 4 figures, 3 tablesIn batch cultures of four Mediterranean strains (from France, Italy, and Spain) of Alexandrium catenella (Whedon et Kof.) Balech growing on a daily light cycle, ammonium and urea uptake were estimated by the 15N tracer technique. Ammonium uptake could be described by Michaelis-Menten kinetics along a substrate gradient of 0.1-10 μgat N · L−1 for the four strains, while two different patterns were observed for urea uptake with Michaelis-Menten kinetics for one strain and linear kinetics for the others. In all cases, an increase in uptake rates with time was noted over the daylight period. This trend led to a net increase in the maximum uptake rate (Vmax; for saturable kinetics) and in the initial slope α. For ammonium, Vmax increased by a factor of 2-10 depending on the strain, and, for urea, the maximal uptake rates measured increased by a factor of 2-18. Temporal variations of half-saturation constants (Ks) for both nutrients did not show a clear trend. Increases in Vmax and α showed an acclimation of the cells' uptake system over time to a N pulse, which may be explained by the light periodicity. For two strains, extensive ammonium release was observed during urea assimilation. This mechanism removes urea from the medium, so it is no longer available to other potential competitors, but supplies N back to the medium in the form of ammonium. From a methodological point of view, the phenomenon leads to considerable underestimates of the contribution of urea to phytoplankton growthThe authors wish to thank R. Ventosa for the nutrient analyses. We thank S. Fraga for the strain ACATA4. This study was financed by the CNRS (Centre National de la Recherche cientifique) and Ifremer (Institut Français pour l’Exploitation de la Mer), as well as the EU-funded Research Project SEED (Life cycle transformations among HAB species, and the environmental and physiological factors that regulate them, GOCE-CT-2005-003875). E. G.’s work was sustained by a Ramon y Cajal contract from the Spanish Ministry of Science and Education. This work benefited from correspondence with Dr. T. A. V. ReesPeer reviewe

Mass of particulate carbon and nitrogen in suspended matter as a function of volume filtered in several oceanic areas

We address two issues in the determination of particulate carbon and nitrogen in suspended matter of aquatic environments. One is the adsorption of dissolved organic matter on filters, leading to overestimate particulate matter. The second is the material loss during filtration due to fragile algal cells breaking up. Examples from both laboratory cultures and natural samples are presented. We recommend using stacked filters in order to estimate thefirst and filtering different volumes of water in order to evaluate the second

From growth to aging, roles and fates of ysosomes (orange-red bodies) in benthic dinoflagellates cells

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The Impact of Associated Bacteria On Morphology and Physiology of the Dinoflagellate \u3ci\u3eAlexandrium tamarense\u3c/i\u3e

Despite their potential impact on phytoplankton dynamics and biogeochemical cycles, biological associations between algae and bacteria are still poorly understood. The aim of the present work was to characterize the influence of bacteria on the growth and function of the dinoflagellate Alexandrium tamarense. Axenic microalgal cultures were inoculated with a microbial community and the resulting cultures were monitored over a 15-month period, in order to allow for the establishment of specific algal–bacterial associations. Algal cells maintained in these new mixed cultures first experienced a period of growth inhibition. After several months, algal growth and cell volume increased, and indicators of photosynthetic function also improved. Our results suggest that community assembly processes facilitated the development of mutualistic relationships between A. tamarense cells and bacteria. These interactions had beneficial effects on the alga that may be only partly explained by mixotrophy of A. tamarense cells. The potential role of organic exudates in the establishment of these algal–bacterial associations is discussed. The present results do not support a role for algal–bacterial interactions in dinoflagellate toxin synthesis. However, variations observed in the toxin profile of A. tamarense cells during culture experiments give new clues for the understanding of biosynthetic pathways of saxitoxin, a potent phycotoxin