The Experts below are selected from a list of 1611 Experts worldwide ranked by ideXlab platform
François-yves Bouget - One of the best experts on this subject based on the ideXlab platform.
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Table_2_Ostreococcus tauri Luminescent Reporter Lines as Biosensors for Detecting Pollution From Copper-Mine Tailing Effluents in Coastal Environments.DOCX
2018Co-Authors: Carlos Henríquez-castillo, Jean-claude Lozano, Hugo Botebol, Adelaide Mouton, Gaelle Lelandais, Santiago Andrade, Salvador Ramírez-flandes, Nicole Trefault, Rodrigo De La Iglesia, François-yves BougetAbstract:Phytoplankton cells are excellent biosensors for environmental monitoring and toxicity assessments in different natural systems. Green algae, in particular, appear to be more responsive to copper (Cu) disturbances. This is interesting considering that Cu pollution in coastal environments has increased over the last century, with enormous repercussions to marine ecosystems. Unfortunately, no high-throughput method exists for the environmental monitoring of Cu toxicity in seawater. To assess potential uses as biosensors of Cu pollution, high-throughput screening was performed on five luminescence reporter lines constructed in the green algae Ostreococcus tauri RCC745. The reporter line expressing the iron storage ferritin protein fused to luciferase (Fer-Luc) was the most sensitive, responding to Cu concentrations in the μM range. Fer-Luc was also the most sensitive reporter line for detecting toxicity in mining-derived polluted seawater predominantly contaminated by soluble Cu. Nevertheless, the Cyclin-Dependent-Kinase A (CDKA) reporter was most suitable for detecting the toxicity of copper-mine tailing effluents containing other metals (e.g., iron). These results highlight that Ostreococcus biosensors can serve as a reliable, inexpensive, and automated, high-throughput laboratory approach for performing seawater analyses of coastal areas subjected to metal disturbances. When challenged with Cu, O. tauri not only evidenced a rapid, transcriptional response for the tested genes, but also showed changes in a broad range of genes, especially as related to the stress response. Overall, the obtained results reinforce that a single biosensor is insufficient when dealing with complex mixtures of toxic compounds in natural environments.
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Image_2_Ostreococcus tauri Luminescent Reporter Lines as Biosensors for Detecting Pollution From Copper-Mine Tailing Effluents in Coastal Environments.JPEG
2018Co-Authors: Carlos Henríquez-castillo, Jean-claude Lozano, Hugo Botebol, Adelaide Mouton, Gaelle Lelandais, Santiago Andrade, Salvador Ramírez-flandes, Nicole Trefault, Rodrigo De La Iglesia, François-yves BougetAbstract:Phytoplankton cells are excellent biosensors for environmental monitoring and toxicity assessments in different natural systems. Green algae, in particular, appear to be more responsive to copper (Cu) disturbances. This is interesting considering that Cu pollution in coastal environments has increased over the last century, with enormous repercussions to marine ecosystems. Unfortunately, no high-throughput method exists for the environmental monitoring of Cu toxicity in seawater. To assess potential uses as biosensors of Cu pollution, high-throughput screening was performed on five luminescence reporter lines constructed in the green algae Ostreococcus tauri RCC745. The reporter line expressing the iron storage ferritin protein fused to luciferase (Fer-Luc) was the most sensitive, responding to Cu concentrations in the μM range. Fer-Luc was also the most sensitive reporter line for detecting toxicity in mining-derived polluted seawater predominantly contaminated by soluble Cu. Nevertheless, the Cyclin-Dependent-Kinase A (CDKA) reporter was most suitable for detecting the toxicity of copper-mine tailing effluents containing other metals (e.g., iron). These results highlight that Ostreococcus biosensors can serve as a reliable, inexpensive, and automated, high-throughput laboratory approach for performing seawater analyses of coastal areas subjected to metal disturbances. When challenged with Cu, O. tauri not only evidenced a rapid, transcriptional response for the tested genes, but also showed changes in a broad range of genes, especially as related to the stress response. Overall, the obtained results reinforce that a single biosensor is insufficient when dealing with complex mixtures of toxic compounds in natural environments.
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Comparative Analysis of Culture Conditions for the Optimization of Carotenoid Production in Several Strains of the Picoeukaryote Ostreococcus
Marine drugs, 2018Co-Authors: Jean-baptiste Guyon, Jean-claude Lozano, Valérie Vergé, Philippe Schatt, Marion Liennard, François-yves BougetAbstract:Microalgae are promising sources for the sustainable production of compounds of interest for biotechnologies. Compared to higher plants, microalgae have a faster growth rate and can be grown in industrial photobioreactors. The microalgae biomass contains specific metabolites of high added value for biotechnology such as lipids, polysaccharides or carotenoid pigments. Studying carotenogenesis is important for deciphering the mechanisms of adaptation to stress tolerance as well as for biotechnological production. In recent years, the picoeukaryote Ostreococcus tauri has emerged as a model organism thanks to the development of powerful genetic tools. Several strains of Ostreococcus isolated from different environments have been characterized with respect to light response or iron requirement. We have compared the carotenoid contents and growth rates of strains of Ostreococcus (OTTH595, RCC802 and RCC809) under a wide range of light, salinity and temperature conditions. Carotenoid profiles and productivities varied in a strain-specific and stress-dependent manner. Our results also illustrate that phylogenetically related microalgal strains originating from different ecological niches present specific interests for the production of specific molecules under controlled culture conditions.
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Use of plankton-derived vitamin B1 precursors, especially thiazole-related precursor, by key marine picoeukaryotic phytoplankton
The ISME Journal, 2016Co-Authors: Ryan W. Paerl, Brian Palenik, François-yves Bouget, Jean-claude Lozano, Valérie Vergé, Philippe Schatt, Eric E. Allen, Farooq AzamAbstract:Several cosmopolitan marine picoeukaryotic phytoplankton are B1 auxotrophs requiring exogenous vitamin B1 or precursor to survive. From genomic evidence, representatives of picoeukaryotic phytoplankton (Ostreococcus and Micromonas spp.) were predicted to use known thiazole and pyrimidine B1 precursors to meet their B1 demands, however, recent culture-based experiments could not confirm this assumption. We hypothesized these phytoplankton strains could grow on precursors alone, but required a thiazole-related precursor other the well-known and extensively tested 4-methyl-5-thiazoleethanol. This hypothesis was tested using bioassays and co-cultures of picoeukaryotic phytoplankton and bacteria. We found that specific B1-synthesizing proteobacteria and phytoplankton are sources of a yet-to-be chemically identified thiazole-related precursor(s) that, along with pyrimidine B1 precursor 4-amino-5-hydroxymethyl-2-methylpyrimidine, can support growth of Ostreococcus spp. (also Micromonas spp.) without B1. We additionally found that the B1-synthesizing plankton do not require contact with picoeukaryotic phytoplankton cells to produce thiazole-related precursor(s). Experiments with wild-type and genetically engineered Ostreococcus lines revealed that the thiazole kinase, ThiM, is required for growth on precursors, and that thiazole-related precursor(s) accumulate to appreciable levels in the euphotic ocean. Overall, our results point to thiazole-related B1 precursors as important micronutrients promoting the survival of abundant phytoplankton influencing surface ocean production and biogeochemical cycling.
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efficient gene targeting and foreign dna removal by homologous recombination in the picoeukaryote Ostreococcus
2014Co-Authors: Jean-claude Lozano, Philippe Schatt, Hugo Botebol, Emmanuel Lesuisse, Stephane Blain, Valerie M K Verge, Isabelle A Carre, François-yves BougetAbstract:With fewer than 8000 genes and a minimalist cellular organization, the green picoalga Ostreococcus tauri is one of the simplest photosynthetic eukaryotes. Ostreococcus tauri contains many plant-specific genes but exhibits a very low gene redundancy. The haploid genome is extremely dense with few repeated sequences and rare transposons. Thanks to the implementation of genetic transformation and vectors for inducible overexpression/knockdown this picoeukaryotic alga has emerged in recent years as a model organism for functional genomics analyses and systems biology. Here we report the development of an efficient gene targeting technique which we use to knock out the nitrate reductase and ferritin genes and to knock in a luciferase reporter in frame to the ferritin native protein. Furthermore, we show that the frequency of insertion by homologous recombination is greatly enhanced when the transgene is designed to replace an existing genomic insertion. We propose that a natural mechanism based on homologous recombination may operate to remove inserted DNA sequences from the genome.
Florence Corellou - One of the best experts on this subject based on the ideXlab platform.
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photoreactions of the histidine kinase rhodopsin ot hkr from the marine picoalga Ostreococcus tauri
Biochemistry, 2019Co-Authors: Meike Luck, Florence Corellou, Francisco Velazquez Escobar, Kathrin Glass, Mareikeisabel Sabotke, Rolf Hagedorn, Friedrich Siebert, Peter Hildebrandt, Peter HegemannAbstract:The tiny picoalga, Ostreococcus tauri, originating from the Thau Lagoon is a member of the marine phytoplankton. Because of its highly reduced genome and small cell size, while retaining the fundamental requirements of a eukaryotic photosynthetic cell, it became a popular model organism for studying photosynthesis or circadian clock-related processes. We analyzed the spectroscopic properties of the photoreceptor domain of the histidine kinase rhodopsin Ot-HKR that is suggested to be involved in the light-induced entrainment of the Ostreococcus circadian clock. We found that the rhodopsin, Ot-Rh, dark state absorbs maximally at 505 nm. Exposure to green-orange light led to the accumulation of a blue-shifted M-state-like absorbance form with a deprotonated Schiff base. This Ot-Rh P400 state had an unusually long lifetime of several minutes. A second long-living photoproduct with a red-shifted absorbance, P560, accumulated upon illumination with blue/UVA light. The resulting photochromicity of the rhodopsin is expected to be advantageous to its function as a molecular control element of the signal transducing HKR domains. The light intensity and the ratio of blue vs green light are reflected by the ratio of rhodopsin molecules in the long-living absorbance forms. Furthermore, dark-state absorbance and the photocycle kinetics vary with the salt content of the environment substantially. This observation is attributed to anion binding in the dark state and a transient anion release during the photocycle, indicating that the salinity affects the photoinduced processes.
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photoreactions of the histidine kinase rhodopsin ot hkr from the marine picoalga Ostreococcus tauri
Biochemistry, 2019Co-Authors: Meike Luck, Florence Corellou, Francisco Velazquez Escobar, Kathrin Glass, Mareikeisabel Sabotke, Rolf Hagedorn, Friedrich Siebert, Peter Hildebrandt, Peter HegemannAbstract:The tiny picoalga, Ostreococcus tauri, originating from the Thau Lagoon is a member of the marine phytoplankton. Because of its highly reduced genome and small cell size, while retaining the fundam...
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Photoreactions of the Histidine Kinase Rhodopsin Ot-HKR from the Marine Picoalga Ostreococcus tauri
2019Co-Authors: Meike Luck, Florence Corellou, Kathrin Glass, Mareikeisabel Sabotke, Rolf Hagedorn, Friedrich Siebert, Peter Hildebrandt, Francisco Velázquez Escobar, Peter HegemannAbstract:The tiny picoalga, Ostreococcus tauri, originating from the Thau Lagoon is a member of the marine phytoplankton. Because of its highly reduced genome and small cell size, while retaining the fundamental requirements of a eukaryotic photosynthetic cell, it became a popular model organism for studying photosynthesis or circadian clock-related processes. We analyzed the spectroscopic properties of the photoreceptor domain of the histidine kinase rhodopsin Ot-HKR that is suggested to be involved in the light-induced entrainment of the Ostreococcus circadian clock. We found that the rhodopsin, Ot-Rh, dark state absorbs maximally at 505 nm. Exposure to green-orange light led to the accumulation of a blue-shifted M-state-like absorbance form with a deprotonated Schiff base. This Ot-Rh P400 state had an unusually long lifetime of several minutes. A second long-living photoproduct with a red-shifted absorbance, P560, accumulated upon illumination with blue/UVA light. The resulting photochromicity of the rhodopsin is expected to be advantageous to its function as a molecular control element of the signal transducing HKR domains. The light intensity and the ratio of blue vs green light are reflected by the ratio of rhodopsin molecules in the long-living absorbance forms. Furthermore, dark-state absorbance and the photocycle kinetics vary with the salt content of the environment substantially. This observation is attributed to anion binding in the dark state and a transient anion release during the photocycle, indicating that the salinity affects the photoinduced processes
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Glycerolipidome peculiarities of the smallest green picoeukaryote Ostreococcus tauri
Plant Physiology, 2017Co-Authors: Charlotte Degraeve-guilbault, Claire Bréhélin, Richard Haslam, Olga Sayanova, Glawdys Marie-luce, Juliette Jouhet, Florence CorellouAbstract:The pico-alga Ostreococcus tauri is a minimal photosynthetic eukaryote that has been implemented as model system. O. tauri is known to efficiently produce docosahexaenoic acid (DHA). We provide a comprehensive study of the glycerolipidome of O.tauri and validate this species as model for related picoeukaryotes. Ostreococcus lipids displayed unique features that combined traits from the green and the chromoalveolate lineages. The betaine-lipid diacylglyceryl-hydroxymethyl-trimethyl-β-alanine and phosphatidyldimethylpropanethiol, both hallmarks of chromalveolates, were identified as presumed extraplastidial lipids. DHA was confined to these lipids while plastidial lipids of prokaryotic type were characterized by the overwhelming presence of ωω-3 C18-polyunsaturated fatty acids (PUFA), 18:5 being restricted to galactolipids. C16:4, a FA typical of green microalgae galactolipids, was also a major component of O. tauri extraplastidial lipids while 16:4-CoA species was not detected. Triacylglycerols (TAGs) displayed the complete panel of FAs and many species exhibited combinations of FAs diagnostic for plastidial and extraplastidial lipids. Importantly, under nutrient deprivation 16:4 and ωω-3 C18 PUFAs accumulated into de novo synthesized TAGs while DHA-TAGs species remained rather stable indicating an increased contribution of FAs of plastidial origin to TAG synthesis. Nutrient deprivation further severely downregulated the conversion of 18:3 to 18:4 resulting in obvious inversion of 18:3/18:4 ratio in plastidial lipids, triacylglycerols as well as in acyl-CoAs. The fine-tuned and dynamic regulation of 18:3/18:4 ratio suggested an important physiological role of these FAs in photosynthetic membranes. Acyl position in structural and storage lipids together with acyl-CoA analysis further help to apprehend mechanisms possibly involved in glycerolipid synthesis.
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robust and flexible response of the Ostreococcus tauri circadian clock to light dark cycles of varying photoperiod
FEBS Journal, 2012Co-Authors: Quentin Thommen, François-yves Bouget, Florence Corellou, Benjamin Pfeuty, Marc LefrancAbstract:The green microscopic alga Ostreococcus tauri has recently emerged as a promising model for understanding how circadian clocks, which drive the daily biological rythms of many organisms, synchronize to the day/night cycle in changing weather and seasons. Here, we analyze translational reporter time series data of its central clock genes CCA1 and TOC1 for a wide range of daylight durations (photoperiods). The variation of temporal profiles with day duration is complex, with the two actors tracking different moments of the day. Nevertheless, all profiles are accurately reproduced by a simple two-gene transcriptional loop model whose parameters are affected by light only through the photoperiod value. We show that this non-intuitive behavior allows the circadian clock to combine flexibility and robustness to daylight fluctuations.
Nigel Grimsley - One of the best experts on this subject based on the ideXlab platform.
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Simplified Transformation of Ostreococcus tauri Using Polyethylene Glycol.
Genes, 2019Co-Authors: Frédéric Sanchez, Sheree Yau, Herve Moreau, Solène Geffroy, Manon Norest, Nigel GrimsleyAbstract:Ostreococcus tauri is an easily cultured representative of unicellular algae (class Mamiellophyceae) that abound in oceans worldwide. Eight complete 13–22 Mb genomes of phylogenetically divergent species within this class are available, and their DNA sequences are nearly always present in metagenomic data produced from marine samples. Here we describe a simplified and robust transformation protocol for the smallest of these algae (O. tauri). Polyethylene glycol (PEG) treatment was much more efficient than the previously described electroporation protocol. Short (2 min or less) incubation times in PEG gave >104 transformants per microgram DNA. The time of cell recovery after transformation could be reduced to a few hours, permitting the experiment to be done in a day rather than overnight as used in previous protocols. DNA was randomly inserted in the O. tauri genome. In our hands PEG was 20–40-fold more efficient than electroporation for the transformation of O. tauri, and this improvement will facilitate mutagenesis of all of the dispensable genes present in the tiny O. tauri genome.
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Rapidity of Genomic Adaptations to Prasinovirus Infection in a Marine Microalga
Viruses, 2018Co-Authors: Sheree Yau, Herve Moreau, Gaëtan Caravello, Nadège Fonvieille, Élodie Desgranges, Nigel GrimsleyAbstract:Prasinoviruses are large dsDNA viruses commonly found in aquatic systems worldwide, where they can infect and lyse unicellular prasinophyte algae such as Ostreococcus. Host susceptibility is virus strain-specific, but resistance of susceptible Ostreococcus tauri strains to a virulent virus arises frequently. In clonal resistant lines that re-grow, viruses are usually present for many generations, and genes clustered on chromosome 19 show physical rearrangements and differential expression. Here, we investigated changes occurring during the first two weeks after inoculation of the prasinovirus OtV5. By serial dilutions of cultures at the time of inoculation, we estimated the frequency of resistant cells arising in virus-challenged O. tauri cultures to be 10 −3-10 −4 of the inoculated population. Re-growing resistant cells were detectable by flow cytometry 3 days post-inoculation (dpi), visible re-greening of cultures occurred by 6 dpi, and karyotypic changes were visually detectable at 8 dpi. Resistant cell lines showed a modified spectrum of host-virus specificities and much lower levels of OtV5 adsorption.
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A Viral Immunity Chromosome in the Marine Picoeukaryote, Ostreococcus tauri
PLoS Pathogens, 2017Co-Authors: Sheree Yau, Claire Hemon, Gwenaë Piganeau, Herve Moreau, Evelyne Derelle, Nigel GrimsleyAbstract:Micro-algae of the genus Ostreococcus and related species of the order Mamiellales are globally distributed in the photic zone of world's oceans where they contribute to fixation of atmospheric carbon and production of oxygen, besides providing a primary source of nutrition in the food web. Their tiny size, simple cells, ease of culture, compact genomes and susceptibility to the most abundant large DNA viruses in the sea render them attractive as models for integrative marine biology. In culture, spontaneous resistance to viruses occurs frequently. Here, we show that virus-producing resistant cell lines arise in many independent cell lines during lytic infections, but over two years, more and more of these lines stop producing viruses. We observed sweeping over-expression of all genes in more than half of chromosome 19 in resistant lines, and karyotypic analyses showed physical rearrangements of this chromosome. Chromosome 19 has an unusual genetic structure whose equivalent is found in all of the sequenced genomes in this ecologically important group of green algae.
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Diversity of Viruses Infecting the Green Microalga Ostreococcus lucimarinus.
Journal of Virology, 2015Co-Authors: Evelyne Derelle, Alexandra Z. Worden, Nigel Grimsley, Adam Monier, Richard Cooke, Herve MoreauAbstract:The functional diversity of eukaryotic viruses infecting a single host strain from seawater samples originating from distant marine locations is unknown. To estimate this diversity, we used lysis plaque assays to detect viruses that infect the widespread species Ostreococcus lucimarinus, which is found in coastal and mesotrophic systems, and O. tauri, which was isolated from coastal and lagoon sites from the northwest Mediterranean Sea. Detection of viral lytic activities against O. tauri was not observed using seawater from most sites, except those close to the area where the host strain was isolated. In contrast, the more cosmopolitan O. lucimarinus species recovered viruses from locations in the Atlantic and Pacific Oceans and the Mediterranean Sea. Six new O. lucimarinus viruses (OlVs) then were characterized and their genomes sequenced. Two subgroups of OlVs were distinguished based on their genetic distances and on the inversion of a central 32-kb-long DNA fragment, but overall their genomes displayed a high level of synteny. The two groups did not correspond to proximity of isolation sites, and the phylogenetic distance between these subgroups was higher than the distances observed among viruses infecting O. tauri. Our study demonstrates that viruses originating from very distant sites are able to infect the same algal host strain and can be more diverse than those infecting different species of the same genus. Finally, distinctive features and evolutionary distances between these different viral subgroups does not appear to be linked to biogeography of the viral isolates. Marine eukaryotic phytoplankton virus diversity has yet to be addressed, and more specifically, it is unclear whether diversity is connected to geographical distance and whether differential infection and lysis patterns exist among such viruses that infect the same host strain. Here, we assessed the genetic distance of geographically segregated viruses that infect the ubiquitous green microalga Ostreococcus. This study provides the first glimpse into the diversity of predicted gene functions in Ostreococcus viruses originating from distant sites and provides new insights into potential host distributions and restrictions in the world oceans.
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bacteria in Ostreococcus tauri cultures friends foes or hitchhikers
Frontiers in Microbiology, 2014Co-Authors: Gwenael Piganeau, Nigel Grimsley, Sophie S Abby, Marie Touchon, Aurelien De JodeAbstract:Marine phytoplankton produce half of the oxygen we breathe and their astounding diversity is just starting to be unravelled. Many microbial phytoplankton are thought to be phototrophic, depending solely on inorganic sources of carbon and minerals for growth rather than preying on other planktonic cells. However, there is increasing evidence that symbiotic associations, to a large extent with bacteria, are required for vitamin or nutrient uptake for many eukaryotic microalgae. Here, we use in silico approaches to look for putative symbiotic interactions by analysing the gene content of microbial communities associated with 13 different Ostreococcus tauri (Chlorophyta, Mamilleophyceae) cultures sampled from the Mediterranean Sea. While we find evidence for bacteria in all cultures, there is no ubiquitous bacterial group, and the most prevalent group, Flavobacteria, is present in 10 out of 13 cultures. We detected genes predicted to encode at least 7 type 3 secretion systems (T3SS) and 6 putative T6SS in 7 microbiomes. Phylogenetic analyses show that the corresponding genes are closely related to genes of systems identified in bacterial-plant interactions, suggesting that these T3SS might be involved in cell-to-cell interactions with O. tauri.
Herve Moreau - One of the best experts on this subject based on the ideXlab platform.
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Simplified Transformation of Ostreococcus tauri Using Polyethylene Glycol.
Genes, 2019Co-Authors: Frédéric Sanchez, Sheree Yau, Herve Moreau, Solène Geffroy, Manon Norest, Nigel GrimsleyAbstract:Ostreococcus tauri is an easily cultured representative of unicellular algae (class Mamiellophyceae) that abound in oceans worldwide. Eight complete 13–22 Mb genomes of phylogenetically divergent species within this class are available, and their DNA sequences are nearly always present in metagenomic data produced from marine samples. Here we describe a simplified and robust transformation protocol for the smallest of these algae (O. tauri). Polyethylene glycol (PEG) treatment was much more efficient than the previously described electroporation protocol. Short (2 min or less) incubation times in PEG gave >104 transformants per microgram DNA. The time of cell recovery after transformation could be reduced to a few hours, permitting the experiment to be done in a day rather than overnight as used in previous protocols. DNA was randomly inserted in the O. tauri genome. In our hands PEG was 20–40-fold more efficient than electroporation for the transformation of O. tauri, and this improvement will facilitate mutagenesis of all of the dispensable genes present in the tiny O. tauri genome.
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Rapidity of Genomic Adaptations to Prasinovirus Infection in a Marine Microalga
Viruses, 2018Co-Authors: Sheree Yau, Herve Moreau, Gaëtan Caravello, Nadège Fonvieille, Élodie Desgranges, Nigel GrimsleyAbstract:Prasinoviruses are large dsDNA viruses commonly found in aquatic systems worldwide, where they can infect and lyse unicellular prasinophyte algae such as Ostreococcus. Host susceptibility is virus strain-specific, but resistance of susceptible Ostreococcus tauri strains to a virulent virus arises frequently. In clonal resistant lines that re-grow, viruses are usually present for many generations, and genes clustered on chromosome 19 show physical rearrangements and differential expression. Here, we investigated changes occurring during the first two weeks after inoculation of the prasinovirus OtV5. By serial dilutions of cultures at the time of inoculation, we estimated the frequency of resistant cells arising in virus-challenged O. tauri cultures to be 10 −3-10 −4 of the inoculated population. Re-growing resistant cells were detectable by flow cytometry 3 days post-inoculation (dpi), visible re-greening of cultures occurred by 6 dpi, and karyotypic changes were visually detectable at 8 dpi. Resistant cell lines showed a modified spectrum of host-virus specificities and much lower levels of OtV5 adsorption.
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A Viral Immunity Chromosome in the Marine Picoeukaryote, Ostreococcus tauri
PLoS Pathogens, 2017Co-Authors: Sheree Yau, Claire Hemon, Gwenaë Piganeau, Herve Moreau, Evelyne Derelle, Nigel GrimsleyAbstract:Micro-algae of the genus Ostreococcus and related species of the order Mamiellales are globally distributed in the photic zone of world's oceans where they contribute to fixation of atmospheric carbon and production of oxygen, besides providing a primary source of nutrition in the food web. Their tiny size, simple cells, ease of culture, compact genomes and susceptibility to the most abundant large DNA viruses in the sea render them attractive as models for integrative marine biology. In culture, spontaneous resistance to viruses occurs frequently. Here, we show that virus-producing resistant cell lines arise in many independent cell lines during lytic infections, but over two years, more and more of these lines stop producing viruses. We observed sweeping over-expression of all genes in more than half of chromosome 19 in resistant lines, and karyotypic analyses showed physical rearrangements of this chromosome. Chromosome 19 has an unusual genetic structure whose equivalent is found in all of the sequenced genomes in this ecologically important group of green algae.
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Diversity of Viruses Infecting the Green Microalga Ostreococcus lucimarinus.
Journal of Virology, 2015Co-Authors: Evelyne Derelle, Alexandra Z. Worden, Nigel Grimsley, Adam Monier, Richard Cooke, Herve MoreauAbstract:The functional diversity of eukaryotic viruses infecting a single host strain from seawater samples originating from distant marine locations is unknown. To estimate this diversity, we used lysis plaque assays to detect viruses that infect the widespread species Ostreococcus lucimarinus, which is found in coastal and mesotrophic systems, and O. tauri, which was isolated from coastal and lagoon sites from the northwest Mediterranean Sea. Detection of viral lytic activities against O. tauri was not observed using seawater from most sites, except those close to the area where the host strain was isolated. In contrast, the more cosmopolitan O. lucimarinus species recovered viruses from locations in the Atlantic and Pacific Oceans and the Mediterranean Sea. Six new O. lucimarinus viruses (OlVs) then were characterized and their genomes sequenced. Two subgroups of OlVs were distinguished based on their genetic distances and on the inversion of a central 32-kb-long DNA fragment, but overall their genomes displayed a high level of synteny. The two groups did not correspond to proximity of isolation sites, and the phylogenetic distance between these subgroups was higher than the distances observed among viruses infecting O. tauri. Our study demonstrates that viruses originating from very distant sites are able to infect the same algal host strain and can be more diverse than those infecting different species of the same genus. Finally, distinctive features and evolutionary distances between these different viral subgroups does not appear to be linked to biogeography of the viral isolates. Marine eukaryotic phytoplankton virus diversity has yet to be addressed, and more specifically, it is unclear whether diversity is connected to geographical distance and whether differential infection and lysis patterns exist among such viruses that infect the same host strain. Here, we assessed the genetic distance of geographically segregated viruses that infect the ubiquitous green microalga Ostreococcus. This study provides the first glimpse into the diversity of predicted gene functions in Ostreococcus viruses originating from distant sites and provides new insights into potential host distributions and restrictions in the world oceans.
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Morphology, genome plasticity, and phylogeny in the genus Ostreococcus reveal a cryptic species, O. mediterraneus sp. nov. (Mamiellales, Mamiellophyceae).
Protist, 2013Co-Authors: Lucie Subirana, Gwenael Piganeau, Yves Desdevises, Evelyne Derelle, Birger Marin, Bérangère Péquin, Stephanie Michely, Marie-line Escande, Julie Meilland, Herve MoreauAbstract:Coastal marine waters in many regions worldwide support abundant populations of extremely small (1-3 μm diameter) unicellular eukaryotic green algae, dominant taxa including several species in the class Mamiellophyceae. Their diminutive size conceals surprising levels of genetic diversity and defies classical species’ descriptions. We present a detailed analysis within the genus Ostreococcus and show that morphological characteristics cannot be used to describe diversity within this group. Karyotypic analyses of the best-characterized species O. tauri show it to carry two chromosomes that vary in size between individual clonal lines, probably an evolutionarily ancient feature that emerged before species’ divergences within the Mamiellales. By using a culturing technique specifically adapted to members of the genus Ostreococcus , we purified >30 clonal lines of a new species, Ostreococcus mediterraneus sp. nov. , previously known as Ostreococcus clade D, that has been overlooked in several studies based on PCR-amplification of genetic markers from environment-extracted DNA. Phylogenetic analyses of the S-adenosylmethionine synthetase gene, and of the complete small subunit ribosomal RNA gene, including detailed comparisons of predicted ITS2 (internal transcribed spacer 2) secondary structures, clearly support that this is a separate species. In addition, karyotypic analyses reveal that the chromosomal location of its ribosomal RNA gene cluster differs from other Ostreococcus clades.
Gwenael Piganeau - One of the best experts on this subject based on the ideXlab platform.
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Spontaneous Mutation Rate in the Smallest Photosynthetic Eukaryotes.
Molecular Biology and Evolution, 2017Co-Authors: Marc Krasovec, Adam Eyre-walker, Sophie Sanchez-ferandin, Gwenael PiganeauAbstract:Mutation is the ultimate source of genetic variation, and knowledge of mutation rates is fundamental for our understanding of all evolutionary processes. High throughput sequencing of mutation accumulation lines has provided genome wide spontaneous mutation rates in a dozen model species, but estimates from nonmodel organisms from much of the diversity of life are very limited. Here, we report mutation rates in four haploid marine bacterial-sized photosynthetic eukaryotic algae; Bathycoccus prasinos, Ostreococcus tauri, Ostreococcus mediterraneus, and Micromonas pusilla. The spontaneous mutation rate between species varies from μ = 4.4 × 10−10 to 9.8 × 10−10 mutations per nucleotide per generation. Within genomes, there is a two-fold increase of the mutation rate in intergenic regions, consistent with an optimization of mismatch and transcription-coupled DNA repair in coding sequences. Additionally, we show that deviation from the equilibrium GC content increases the mutation rate by ∼2% to ∼12% because of a GC bias in coding sequences. More generally, the difference between the observed and equilibrium GC content of genomes explains some of the inter-specific variation in mutation rates.
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bacteria in Ostreococcus tauri cultures friends foes or hitchhikers
Frontiers in Microbiology, 2014Co-Authors: Gwenael Piganeau, Nigel Grimsley, Sophie S Abby, Marie Touchon, Aurelien De JodeAbstract:Marine phytoplankton produce half of the oxygen we breathe and their astounding diversity is just starting to be unravelled. Many microbial phytoplankton are thought to be phototrophic, depending solely on inorganic sources of carbon and minerals for growth rather than preying on other planktonic cells. However, there is increasing evidence that symbiotic associations, to a large extent with bacteria, are required for vitamin or nutrient uptake for many eukaryotic microalgae. Here, we use in silico approaches to look for putative symbiotic interactions by analysing the gene content of microbial communities associated with 13 different Ostreococcus tauri (Chlorophyta, Mamilleophyceae) cultures sampled from the Mediterranean Sea. While we find evidence for bacteria in all cultures, there is no ubiquitous bacterial group, and the most prevalent group, Flavobacteria, is present in 10 out of 13 cultures. We detected genes predicted to encode at least 7 type 3 secretion systems (T3SS) and 6 putative T6SS in 7 microbiomes. Phylogenetic analyses show that the corresponding genes are closely related to genes of systems identified in bacterial-plant interactions, suggesting that these T3SS might be involved in cell-to-cell interactions with O. tauri.
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Morphology, genome plasticity, and phylogeny in the genus Ostreococcus reveal a cryptic species, O. mediterraneus sp. nov. (Mamiellales, Mamiellophyceae).
Protist, 2013Co-Authors: Lucie Subirana, Gwenael Piganeau, Yves Desdevises, Evelyne Derelle, Birger Marin, Bérangère Péquin, Stephanie Michely, Marie-line Escande, Julie Meilland, Herve MoreauAbstract:Coastal marine waters in many regions worldwide support abundant populations of extremely small (1-3 μm diameter) unicellular eukaryotic green algae, dominant taxa including several species in the class Mamiellophyceae. Their diminutive size conceals surprising levels of genetic diversity and defies classical species’ descriptions. We present a detailed analysis within the genus Ostreococcus and show that morphological characteristics cannot be used to describe diversity within this group. Karyotypic analyses of the best-characterized species O. tauri show it to carry two chromosomes that vary in size between individual clonal lines, probably an evolutionarily ancient feature that emerged before species’ divergences within the Mamiellales. By using a culturing technique specifically adapted to members of the genus Ostreococcus , we purified >30 clonal lines of a new species, Ostreococcus mediterraneus sp. nov. , previously known as Ostreococcus clade D, that has been overlooked in several studies based on PCR-amplification of genetic markers from environment-extracted DNA. Phylogenetic analyses of the S-adenosylmethionine synthetase gene, and of the complete small subunit ribosomal RNA gene, including detailed comparisons of predicted ITS2 (internal transcribed spacer 2) secondary structures, clearly support that this is a separate species. In addition, karyotypic analyses reveal that the chromosomal location of its ribosomal RNA gene cluster differs from other Ostreococcus clades.
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Organellar Inheritance in the Green Lineage: Insights from Ostreococcus tauri
Genome Biology and Evolution, 2013Co-Authors: Romain Blanc-mathieu, Adam Eyre-walker, Sophie Sanchez-ferandin, Gwenael PiganeauAbstract:Along the green lineage (Chlorophyta and Streptophyta), mitochondria and chloroplast are mainly uniparentally transmitted and their evolution is thus clonal. The mode of organellar inheritance in their ancestor is less certain. The inability to make clear phylogenetic inference is partly due to a lack of information for deep branching organisms in this lineage. Here, we investigate organellar evolution in the early branching green alga Ostreococcus tauri using population genomics data from the complete mitochondrial and chloro-plast genomes. The haplotype structure is consistent with clonal evolution in mitochondria, while we find evidence for recombination in the chloroplast genome. The number of recombination events in the genealogy of the chloroplast suggests that recombination, and thus biparental inheritance, is not rare. Consistent with the evidence of recombination, we find that the ratio of the number of nonsynonymous to the synonymous polymorphisms per site is lower in chloroplast than in the mitochondria genome. We also find evidence for the segregation of two selfish genetic elements in the chloroplast. These results shed light on the role of recombination and the evolutionary history of organellar inheritance in the green lineage.
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cryptic sex in the smallest eukaryotic marine green alga
Molecular Biology and Evolution, 2010Co-Authors: Gwenael Piganeau, Herve Moreau, Nigel Grimsley, Bérangère Péquin, Charles BachyAbstract:Ostreococcus spp. are common worldwide oceanic picoeukaryotic pelagic algae. The complete genomes of three strains from different ecological niches revealed them to represent biologically distinct species despite their identical cellular morphologies (cryptic species). Their tiny genomes (13 Mb), with ;20 chromosomes, are colinear and densely packed with coding sequences, but no sexual life cycle has been described. Seventeen new strains of one of these species, Ostreococcus tauri, were isolated from 98 seawater samplings from the NW Mediterranean by filtering, culturing, cloning, and plating for single colonies and identification by sequencing their ribosomal 18S gene. In order to find the genetic markers for detection of polymorphisms and sexual recombination, we used an in silico approach to screen available genomic data. Intergenic regions of DNA likely to evolve neutrally were analyzed following polymerase chain reaction amplification of sequences using flanking primers from adjacent conserved coding sequences that were present as syntenic pairs in two different species of Ostreococcus. Analyses of such DNA regions from eight marker loci on two chromosomes from each strain revealed that the isolated O. tauri clones were haploid and that the overall level of polymorphism was ;0.01. Four different genetic tests for recombination showed that sexual exchanges must be inferred to account for the between-locus and between-chromosome marker combinations observed. However, our data suggest that sexual encounters are infrequent because we estimate the frequency of meioses/mitoses among the sampled strains to be 10 � 6 . Ostreococcus tauri and related species encode and express core genes for mitosis and meiosis, but their mechanisms of cell division and recombination, nevertheless, remain enigmatic because a classical eukaryotic spindle with 40 canonical microtubules would be much too large for the available ;0.9-lm 3 cellular volume.
