Biology subjects

Curien, G.

Publications and source records attributed to Curien, G..

5 recordsLinked to original sources

bioRxiv2023

Sweet and fatty symbionts: photosynthetic productivity and carbon storage boosted in microalgae within a host

Symbiosis between a host and intracellular eukaryotic microalgae is a widespread life strategy in aquatic ecosystems. This partnership is considered to be mainly energized by the photosynthetically-derived carbon energy of microalgal symbionts. A major question is whether microalgae increase their photosynthetic production and decrease carbon storage in order to maximize carbon translocation to their host. By combining three-dimensional subcellular imaging and physiological analyses, we show that the photosynthetic machinery (chloroplast and CO2-fixing pyrenoid) of the symbiotic microalga Micractinium conductrix significantly expands inside their host (the ciliate Paramecium bursaria) compared to the free-living state. This is accompanied by a 13-fold higher quantity of Rubisco enzymes and 16-fold higher carbon fixation rate. Time-resolved subcellular imaging revealed that photosynthetically-derived carbon is first allocated to starch during the day, with five times higher production in symbiosis despite low growth. Nearly half of the carbon stored in starch is consumed overnight and some accumulates in lipid droplets, which are 20-fold more voluminous in symbiotic microalgae. We also show that carbon is transferred to the host and hypothesize that much of this is respired by the high density of surrounding host mitochondria. We provide evidence that the boosted photosynthetic production of symbiotic microalgae could be explained by the energetic demands of the host. Overall, this study provides an unprecedented view of the subcellular remodeling and dynamics of carbon metabolism of microalgae inside a host, highlighting the potentially key role of the source-sink relationship in aquatic photosymbiosis. Significance statementSymbiotic interactions between a heterotrophic host and intracellular microalgae are widespread in aquatic ecosystems and are considered to be energized by the photosynthetically-derived carbon energy. However, little is known on the impact of symbiosis on the algal bioenergetics (e.g. carbon production and storage). This study reveals the morphological and physiological changes of a microalga inside a host at the subcellular scale over the day. We show that the photosynthetic machinery expands and carbon fixation and storage are boosted in symbiotic microalgae beyond their growth needs. This high photosynthetic production is very likely enhanced by the host energetic demands. Our findings advance our basic understanding of photosymbiosis and open new perspectives on the mechanisms and drivers of metabolic exchange between partners.

physiology↗

bioRxiv2023

Deciphering lipid mutant phenotypes with a new genome-scale metabolic model of Microchloropsis gaditana encompassing detailed lipid metabolism

The oleaginous microalga Microchloropsis gaditana (formerly Nannochloropsis gaditana) has gained large interest due to its potential to produce lipids for a wide range of biotechnological applications. To optimize M. gaditana growth conditions and develop new strains to enhance lipid synthesis and accumulation, a broad understanding of the organism metabolism is essential. Computational models such as genome-scale metabolic models constitute powerful tools for unravelling microorganism metabolism. In this work we present iMgadit23, a new genome-scale metabolic model for M. gaditana. Model covers 2330 reactions involving 1977 metabolites and associated with 889 genes. Pathways involved in membrane and storage glycerolipid biosynthesis and degradation have undergone thorough manual curation and have been comprehensively described based on current knowledge of M. gaditana lipid metabolism. Additionally, we developed a detailed 2D-pathway map of model content to provide a systems-level visualization of M. gaditana metabolism. We demonstrated the predictive capabilities of iMgadit23, validating its ability to qualitatively and quantitatively capture in vivo growth phenotypes under diverse environmental and genetic conditions. Model was also able to capture the role of the Bubblegum acyl-CoA synthetase in remodeling M. gaditana lipid metabolism. iMgadit23 and its 2D map constitute valuable tools to increase understanding of M. gaditana metabolism and deciphering mutant phenotypes, specifically in the context of lipid metabolism. The model holds significant promise in predicting M. gaditana metabolic capabilities, facilitating strain engineering, and optimizing cultivation processes for a broad range of industrial applications.

plant biology↗

bioRxiv2022

Tailoring confocal microscopy for in-cell photophysiology studies

Photoautotrophs environmental responses have been extensively studied at the organism and ecosystem level. However, less is known about their photosynthesis at the single cell level. This information is needed to understand photosynthetic acclimation processes, as light changes as it penetrates cells, layers of cells or organs. Furthermore, cells within the same tissue may behave differently, being at different developmental/physiological stages. Here we describe a new approach for single-cell and subcellular photophysiology based on the customisation of confocal microscopy to assess chlorophyll fluorescence quenching by the saturation pulse method. We exploit this setup to: i. reassess the specialisation of photosynthetic activities in developing tissues of non-vascular plants; ii. identify a specific subpopulation of phytoplankton cells in marine photosymbiosis, which are consolidating metabolic connections with their animal hosts, and iii. testify to the link between light penetration and photoprotection responses inside the different tissues that constitute a plant leaf anatomy. MotivationVisualising photosynthetic responses in 3D is essential for understanding most acclimation processes, as light changes within photosynthetic tissues as it penetrates the absorbing/diffusing layers of the cells. To achieve this goal, we developed a new imaging workflow merging confocal microscopy and saturating pulse chlorophyll fluorescence detection. This method applies to samples characterised by increasing complexity and its simplicity will contribute to its widespread use in plant and microalgae photoacclimation studies.

plant biology↗

bioRxiv2020

In-cell quantitative structural imaging of phytoplankton using 3D electron microscopy

Phytoplankton is a minor fraction of the global biomass playing a major role in primary production and climate. Despite improved understanding of phytoplankton diversity and genomics, we lack nanoscale subcellular imaging approaches to understand their physiology and cell biology. Here, we present a complete Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) workflow (from sample preparation to image processing) to generate nanometric 3D phytoplankton models. Tomograms of entire cells, representatives of six ecologically-successful phytoplankton unicellular eukaryotes, were used for quantitative morphometric analysis. Besides lineage-specific cellular architectures, we observed common features related to cellular energy management: i) conserved cell-volume fractions occupied by the different organelles; ii) consistent plastid-mitochondria interactions, iii) constant volumetric ratios in these energy-producing organelles. We revealed detailed subcellular features related to chromatin organization and to biomineralization. Overall, this approach opens new perspectives to study phytoplankton acclimation responses to abiotic and biotic factors at a relevant biological scale.

plant biology↗

bioRxiv2019

Identification of the Calmodulin-dependent NAD+ kinase sustaining the elicitor-induced oxidative burst in plants

NADP(H) is an essential cofactor ofmultiple metabolic processes in all living organisms. While NADP+ production in plants has long been known to involve a Calmodulin (CaM)/Ca2+-dependent NAD+ kinase, the nature of the enzyme catalyzing this activity has remained enigmatic, as well as its role in plant physiology. Here, we identify an Arabidopsis P-loop ATPase (Atlg04280) with a bacterial type II zeta toxin domain, that catalyzes NADP+ production upon binding of CaM/Ca2+ to a domain located in its N-terminal region. The encoded protein (NADKc-1) is associated with the mitochondria and amplifies the elicitor-induced oxidative burst in Arabidopsis leaves representing the missing link between calcium signalling and metabolism in the response to pathogen elicitor. By analysis of various plants and algae, we show that NADKc is well conserved in the plant lineage and present in basal plants. Our data allows proposing that the CaM-dependent NAD kinase activity is only found in photosynthetic species carrying NADKc-1 related proteins, which would represent the only proteins harboring CaM-dependent NAD kinase activity in plants and algae.

plant biology↗