Geslin Emmanuelle

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Geslin
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Emmanuelle
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  • Preprint
    Ultrastructure and distribution of kleptoplasts in benthic foraminifera from shallow-water (photic) habitats
    ( 2017-10) Jauffrais, Thierry ; LeKieffre, Charlotte ; Koho, Karoliina ; Tsuchiya, Masashi ; Schweizer, Magali ; Bernhard, Joan M. ; Meibom, Anders ; Geslin, Emmanuelle
    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.
  • Article
    Deposit-feeding of Nonionellina labradorica (foraminifera) from an Arctic methane seep site and possible association with a methanotroph
    (European Geosciences Union, 2022-08-30) Schmidt, Christiane ; Geslin, Emmanuelle ; Bernhard, Joan M. ; LeKieffre, Charlotte ; Svenning, Mette Marianne ; Roberge, Hélène ; Schweizer, Magali ; Panieri, Giuliana
    Several foraminifera are deposit feeders that consume organic detritus (dead particulate organic material with entrained bacteria). However, the role of such foraminifera in the benthic food web remains understudied. Foraminifera feeding on methanotrophic bacteria, which are 13C-depleted, may cause negative cytoplasmic and/or calcitic δ13C values. To test whether the foraminiferal diet includes methanotrophs, we performed a short-term (20 h) feeding experiment with Nonionellina labradorica from an active Arctic methane-emission site (Storfjordrenna, Barents Sea) using the marine methanotroph Methyloprofundus sedimenti and analysed N. labradorica cytology via transmission electron microscopy (TEM). We hypothesised that M. sedimenti would be visible post-experiment in degradation vacuoles, as evidenced by their ultrastructure. Sediment grains (mostly clay) occurred inside one or several degradation vacuoles in all foraminifers. In 24 % of the specimens from the feeding experiment degradation vacuoles also contained bacteria, although none could be confirmed to be the offered M. sedimenti. Observations of the apertural area after 20 h incubation revealed three putative methanotrophs, close to clay particles, based on bacterial ultrastructural characteristics. Furthermore, we noted the absence of bacterial endobionts in all examined N. labradorica but confirmed the presence of kleptoplasts, which were often partially degraded. In sum, we suggest that M. sedimenti can be consumed via untargeted grazing in seeps and that N. labradorica can be generally classified as a deposit feeder at this Arctic site.
  • Preprint
    Innovative TEM-coupled approaches to study foraminiferal cells
    ( 2017-10) Nomaki, Hidetaka ; LeKieffre, Charlotte ; Escrig, Stéphane ; Meibom, Anders ; Yagyu, Shinsuke ; Richardson, Elizabeth A. ; Matsuzaki, Takuya ; Murayama, Masafumi ; Geslin, Emmanuelle ; Bernhard, Joan M.
    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.
  • Article
    Ammonium and sulfate assimilation is widespread in benthic foraminifera
    (Frontiers Media, 2022-07-20) LeKieffre, Charlotte ; Jauffrais, Thierry ; Bernhard, Joan M. ; Filipsson, Helena L. ; Schmidt, Christiane ; Roberge, Hélène ; Maire, Olivier ; Panieri, Giuliana ; Geslin, Emmanuelle ; Meibom, Anders
    Nitrogen and sulfur are key elements in the biogeochemical cycles of marine ecosystems to which benthic foraminifera contribute significantly. Yet, cell-specific assimilation of ammonium, nitrate and sulfate by these protists is poorly characterized and understood across their wide range of species-specific trophic strategies. For example, detailed knowledge about ammonium and sulfate assimilation pathways is lacking and although some benthic foraminifera are known to maintain intracellular pools of nitrate and/or to denitrify, the potential use of nitrate-derived nitrogen for anabolic processes has not been systematically studied. In the present study, NanoSIMS isotopic imaging correlated with transmission electron microscopy was used to trace the incorporation of isotopically labeled inorganic nitrogen (ammonium or nitrate) and sulfate into the biomass of twelve benthic foraminiferal species from different marine environments. On timescales of twenty hours, no detectable 15N-enrichments from nitrate assimilation were observed in species known to perform denitrification, indicating that, while denitrifying foraminifera store intra-cellular nitrate, they do not use nitrate-derived nitrogen to build their biomass. Assimilation of both ammonium and sulfate, with corresponding 15N and 34S-enrichments, were observed in all species investigated (with some individual exceptions for sulfate). Assimilation of ammonium and sulfate thus can be considered widespread among benthic foraminifera. These metabolic capacities may help to underpin the ability of benthic foraminifera to colonize highly diverse marine habitats.
  • Article
    An overview of cellular ultrastructure in benthic foraminifera : new observations of rotalid species in the context of existing literature
    (Elsevier, 2017-10-19) LeKieffre, Charlotte ; Bernhard, Joan M. ; Mabilleau, Guillaume ; Filipsson, Helena L. ; Meibom, Anders ; Geslin, Emmanuelle
    We report systematic transmission electron microscope (TEM) observations of the cellular ultrastructure of selected, small rotalid benthic foraminifera. Nine species from different environments (intertidal mudflat, fjord, and basin) were investigated: Ammonia sp., Elphidium oceanense, Haynesina germanica, Bulimina marginata, Globobulimina sp., Nonionellina labradorica, Nonionella sp., Stainforthia fusiformis and Buliminella tenuata. All the observed specimens were fixed just after collection from their natural habitats allowing description of intact and healthy cells. Foraminiferal organelles can be divided into two broad categories: (1) organelles that are present in all eukaryotes, such as the nuclei, mitochondria, endoplasmic reticulum, Golgi apparatus, and peroxisomes; and (2) organelles observed in all foraminifera but not common in all eukaryotic cells, generally with unknown function, such as fibrillar vesicles or electron-opaque bodies. Although the organelles of the first category were observed in all the observed species, their appearance varies. For example, subcellular compartments linked to feeding and metabolism exhibited different sizes and shapes between species, likely due to differences in their diet and/or trophic mechanisms. The organelles of the second category are common in all foraminiferal species investigated and, according to the literature, are frequently present in the cytoplasm of many different species, both benthic and planktonic. This study, thus, provides a detailed overview of the major ultrastructural components in benthic foraminiferal cells from a variety of marine environments, and also highlights the need for further research to better understand the function and role of the various organelles in these fascinating organisms.
  • Preprint
  • Article
    Inorganic carbon and nitrogen assimilation in cellular compartments of a benthic kleptoplastic foraminifer
    (Nature Publishing Group, 2018-07-04) LeKieffre, Charlotte ; Jauffrais, Thierry ; Geslin, Emmanuelle ; Jesus, Bruno ; Bernhard, Joan M. ; Giovani, Maria-Evangelia ; Meibom, Anders
    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.
  • Article
    Microscale imaging sheds light on species-specific strategies for photo-regulation and photo-acclimation of microphytobenthic diatoms
    (Wiley, 2023-09-06) Jesus, Bruno ; Jauffrais, Thierry ; Trampe, Erik ; Meleder, Vona ; Ribeiro, Lourenco ; Bernhard, Joan M. ; Geslin, Emmanuelle ; Kuhl, Michael
    Intertidal microphytobenthic (MPB) biofilms are key sites for coastal primary production, predominantly by pennate diatoms exhibiting photo-regulation via non-photochemical quenching (NPQ) and vertical migration. Movement is the main photo-regulation mechanism of motile (epipelic) diatoms and because they can move from light, they show low-light acclimation features such as low NPQ levels, as compared to non-motile (epipsammic) forms. However, most comparisons of MPB species-specific photo-regulation have used low light acclimated monocultures, not mimicking environmental conditions. Here we used variable chlorophyll fluorescence imaging, fluorescent labelling in sediment cores and scanning electron microscopy to compare the movement and NPQ responses to light of four epipelic diatom species from a natural MPB biofilm. The diatoms exhibited different species-specific photo-regulation features and a large NPQ range, exceeding that reported for epipsammic diatoms. This could allow epipelic species to coexist in compacted light niches of MPB communities. We show that diatom cell orientation within MPB can be modulated by light, where diatoms oriented themselves more perpendicular to the sediment surface under high light vs. more parallel under low light, demonstrating behavioural, photo-regulatory response by varying their light absorption cross-section. This highlights the importance of considering species-specific responses and understanding cell orientation and photo-behaviour in MPB research.