Inorganic carbon and nitrogen assimilation in cellular compartments of a benthic kleptoplastic foraminifer

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Scientific Reports 8 (2018): 10140, doi:10.1038/s41598-018-28455-1.Haynesina germanica, an ubiquitous benthic foraminifer in intertidal mudflats, has the remarkable ability to isolate, sequester, and use chloroplasts from microalgae. The photosynthetic functionality of these kleptoplasts has been demonstrated by measuring photosystem II quantum efficiency and O2 production rates, but the precise role of the kleptoplasts in foraminiferal metabolism is poorly understood. Thus, the mechanism and dynamics of C and N assimilation and translocation from the kleptoplasts to the foraminiferal host requires study. The objective of this study was to investigate, using correlated TEM and NanoSIMS imaging, the assimilation of inorganic C and N (here ammonium, NH4+) in individuals of a kleptoplastic benthic foraminiferal species. H. germanica specimens were incubated for 20 h in artificial seawater enriched with H13CO3− and 15NH4+ during a light/dark cycle. All specimens (n = 12) incorporated 13C into their endoplasm stored primarily in the form of lipid droplets. A control incubation in darkness resulted in no 13C-uptake, strongly suggesting that photosynthesis is the process dominating inorganic C assimilation. Ammonium assimilation was observed both with and without light, with diffuse 15N-enrichment throughout the cytoplasm and distinct 15N-hotspots in fibrillar vesicles, electron-opaque bodies, tubulin paracrystals, bacterial associates, and, rarely and at moderate levels, in kleptoplasts. The latter observation might indicate that the kleptoplasts are involved in N assimilation. However, the higher N assimilation observed in the foraminiferal endoplasm incubated without light suggests that another cytoplasmic pathway is dominant, at least in darkness. This study clearly shows the advantage provided by the kleptoplasts as an additional source of carbon and provides observations of ammonium uptake by the foraminiferal cell.This work was supported by the Swiss National Science Foundation (grant no. 200021_149333) and was part of the CNRS EC2CO-Lefe project ForChlo. It was also supported by the Region Pays de la Loire (Post-doc position of TJ, on FRESCO project) as well as the WHOI Robert W. Morse Chair for Excellence in Oceanography and The Investment in Science Fund at WHOI

Ultrastructure and distribution of kleptoplasts in benthic foraminifera from shallow-water (photic) habitats

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Micropaleontology 138 (2018): 46-62, doi:10.1016/j.marmicro.2017.10.003.Assimilation, sequestration and maintenance of foreign chloroplasts inside an organism is termed “chloroplast sequestration” or “kleptoplasty”. This phenomenon is known in certain benthic foraminifera, in which such kleptoplasts can be found both intact and functional, but with different retention times depending on foraminiferal species. In the present study, seven species of benthic foraminifera (Haynesina germanica, Elphidium williamsoni, E. selseyense, E. oceanense, E. aff. E. crispum, Planoglabratella opercularis and Ammonia sp.) were collected from shallow-water benthic habitats and examined with transmission electron microscope (TEM) for cellular ultrastructure to ascertain attributes of kleptoplasts. Results indicate that all these foraminiferal taxa actively obtain kleptoplasts but organized them differently within their endoplasm. In some species, the kleptoplasts were evenly distributed throughout the endoplasm (e.g., H. germanica, E. oceanense, Ammonia sp.), whereas other species consistently had plastids distributed close to the external cell membrane (e.g., Elphidium williamsoni, E. selseyense, P. opercularis). Chloroplast degradation also seemed to differ between species, as many degraded plastids were found in Ammonia sp. and E. oceanense compared to other investigated species. Digestion ability, along with different feeding and sequestration strategies may explain the differences in retention time between taxa. Additionally, the organization of the sequestered plastids within the endoplasm may also suggest behavioral strategies to expose and/or protect the sequestered plastids to/from light and/or to favor gas and/or nutrient exchange with their surrounding habitats.TJ was funded by the “FRESCO” project, a project supported by the Region Pays de Loire and the University of Angers. This work was also supported by a grant no. 200021_149333 from the Swiss National Science Foundation and the French national program EC2CO-LEFE (project ForChlo).JMB acknowledges the Robert W. Morse Chair for Excellence in Oceanography and the Investment in Science Fund at WHOI. Also, KK acknowledges the Academy of Finland (Project numbers: 278827, 283453)

Laboratory studies on benthic foraminiferal ecology and geochemistry

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Heterotrophic Foraminifera Capable of Inorganic Nitrogen Assimilation

Nitrogen availability often limits biological productivity in marine systems, where inorganic nitrogen such as ammonium is assimilated into the food web by bacteria and photoautotrophic eukaryotes. Recently, ammonium assimilation was observed in kleptoplast-containing protists of the phylum foraminifera, possibly via the glutamine synthetase/glutamate synthase (GS/GOGAT) assimilation pathway imported with the kleptoplasts. However, it is not known if the ubiquitous and diverse heterotrophic protists have an innate ability for ammonium assimilation. Using stable isotope incubations (15N-ammonium and 13C-bicarbonate) and combining transmission electron microscopy (TEM) with quantitative nanoscale secondary ion mass spectrometry (NanoSIMS) imaging, we investigated the uptake and assimilation of dissolved inorganic ammonium by two heterotrophic foraminifera; a non-kleptoplastic benthic species, Ammonia sp., and a planktonic species, Globigerina bulloides. These species are heterotrophic and not capable of photosynthesis. Accordingly, they did not assimilate 13C-bicarbonate. However, both species assimilated dissolved 15N-ammonium and incorporated it into organelles of direct importance for ontogenetic growth and development of the cell. These observations demonstrate that at least some heterotrophic protists have an innate cellular mechanism for inorganic ammonium assimilation, highlighting a newly discovered pathway for dissolved inorganic nitrogen (DIN) assimilation within the marine microbial loop

Innovative TEM-coupled approaches to study foraminiferal cells

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Micropaleontology 138 (2018): 90-104, doi:10.1016/j.marmicro.2017.10.002.Transmission electron microscope (TEM) observation has revealed much about the basic cell biology of foraminifera. Yet, there remains much we do not know about foraminiferal cytology and physiology, especially for smaller benthic foraminifera, which inhabit a wide range of habitats. Recently, some TEM-coupled approaches have been developed to study correlative foraminiferal ecology and physiology in detail: Fluorescently Labeled Embedded Core (FLEC)-TEM for observing foraminiferal life-position together with their cytoplasmic ultrastructure, micro-X-ray computed tomography (CT)-TEM for observing and reconstructing foraminiferal cytoplasm in three dimensions (3D), and TEM-Nanometer-scale secondary ion mass spectrometry (NanoSIMS) for mapping of elemental and isotopic compositions at sub-micrometer resolutions with known ultrastructure. In this contribution, we review and illustrate these recent advances of TEM-coupled methods.This work was financially supported by the Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Scientific Research (C) grant number 17K05697 to HN) and the Swiss National Science Foundation (grant no. 200021_149333). JMB’s contributions were funded by US NSF grants OCE-0551001 and OCE-1634469, the WHOI Robert W. Morse Chair for Excellence in Oceanography, and The Investment in Science Fund at WHOI. The micro-X-ray CT imaging was performed under the cooperative research program of Center for Advanced Marine Core Research (CMCR), Kochi University (accept No. 17A021)

Introduction to the Special Issue entitled “Benthic Foraminiferal Ultrastructure Studies”

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Contributions de la phylogénie moléculaire à la taxonomie des foraminifères : aperçu général et cas pratique avec <i>Pseudoeponides falsobeccarii</i> <xref rid="bib0265" ref-type="bibr">Rouvillois, 1974</xref>

Grâce à la phylogénie moléculaire, il est possible d’aborder la taxonomie des foraminifères sous un nouvel angle, indépendant de la morphologie. Après un aperçu général des apports de la phylogénie moléculaire à la taxonomie des foraminifères, nous présentons un cas pratique. Des séquences appartenant aux gènes de la petite (18S) et de la grande sous-unités (28S) de l’ADN ribosomique (ADNr) de Pseudoeponides falsobeccarii ont été comparées à des séquences semblables de rotaliides disponibles dans GenBank. Leur analyse phylogénétique démontre que P. falsobeccarii appartient au genre Ammonia, parce que les séquences d’ADN de cette espèce se retrouvent à l’intérieur du clade formé par toutes les séquences d’ Ammonia. À l’intérieur de ce clade, Ammonia falsobeccarii forme un groupe bien distinct des autres phylotypes décrits pour Ammonia, ce qui signifie que ce taxon peut être considéré comme une espèce séparée, plutôt qu’un écophénotype d’une autre espèce d’ Ammonia.Molecular phylogenetics gives new insights into the taxonomy of foraminifera, independent of their morphology. After a survey of the present knowledge on how molecular phylogeny can contribute to foraminiferal taxonomy, we present an applied example. The comparison of ribosomal DNA (rDNA) sequences belonging to the SSU (Small Subunit) and LSU (Large Subunit) genes of Pseudoeponides falsobeccarii with other similar sequences of rotaliids available in GenBank shows that this species actually belongs to the genus Ammonia, because it groups inside the other Ammonia sequences instead of forming a distinct clade. Moreover, Ammonia falsobeccarii forms a clade well separated from other Ammonia phylotypes, meaning that it can be considered as a distinct species, and not as an ecophenotype of one of the other Ammonia species.</p

(dir.), Le droit international de la reconnaissance, un instrument de décolonisation et de refondation du droit international ?, Confluence des droits

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"Propos introductifs – Décoloniser et refonder le droit international au prisme de la reconnaissance", pp.11-15

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"Propos introductifs – Décoloniser et refonder le droit international au prisme de la reconnaissance", pp.11-15

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