A new marine picoeucaryote: Ostreococcus tauri gen. et sp. nov. (Chlorophyta, Prasinophyceae)

Chretiennot-Dinet, M. J.; Courties, Claude; Vaquer, André; Neveux, Jacques; Claustre, Hervé; Lautier, Jacques; Machado, Maria-Cordelia

doi:10.2216/i0031-8884-34-4-285.1

Cited by 150 publications

(127 citation statements)

References 29 publications

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“…Picophytoplankton dominates numerically the phytoplankton assemblage in Thau lagoon (Chrétiennot-Dinet et al 1995), but nanoplanktonic diatoms mainly contribute to the phytoplanktonic biomass on a yearly basis. However, in summer, picophytoplankton, and notably Ostreococcus tauri, production is largely responsible for the strong increase of P :B ratios (Courties et al 1994).…”

Section: Discussionmentioning

confidence: 99%

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

Souchu

Vaquer²,

Collos³

et al. 2001

Mar. Ecol. Prog. Ser.

148

108

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Thau lagoon is a Mediterranean shellfish ecosystem with large biomasses of oysters growing in waters with high residence time due to low tidal ranges. The influence of filter feeders (oysters and their epibiota) on the spatial distribution of particulate and dissolved compounds in the water column of Thau lagoon was studied through its variation with time. In 1991/1992, daily variations were investigated in pens, corridors and outside shellfish farming zones for nutrients, chlorophyll a and primary production. Salinity, dissolved oxygen, nutrients, organic matter and chlorophyll a were also monitored in surface waters inside and outside shellfish farming zones each week from January 1993 to March 1994. The presence of shellfish farms led to a decrease by only a few percent of oxygen concentrations in their vicinity, but the mean (± SE) deficits of chlorophyll a and POC concentrations were 44 ± 4% and 26 ± 9% respectively in the eastern zone (8 m). The shift induced by filter feeders in phytoplankton composition favoured picophytoplankton with higher growth rates. But the summer increase in phytoplankton growth rate was stronger than the positive feedback due to filter feeder filtration. Summer was determinant for the growth of oysters owing to enhanced regenerated primary production. During this period, filter feeders were not food limited, while they tended to control phytoplankton biomasses and production the rest of the year. The nutrient excess in shellfish farming zones was highly significant, with increases of 73 ± 16, 36 ± 12 and 19 ± 8% for ammonia, phosphates and silicate respectively in the eastern zone. In the western zone, the nutrient excess was less strong by half for ammonia and phosphate, because the lower depth (4 m) allows light to reach the bottom and enables benthic macroflora to grow on nutrients of benthic origin. The decline of phytoplankton biomasses in shellfish farms induced a decrease in the nutrient demand, especially for ammonia. This situation was likely to favour nitrification, which led during autumn to higher nitrate concentrations within shellfish farming zones than outside. Therefore, filter feeders were able to alter the dominant biogeochemical process in the water column by stimulating nitrification. KEY WORDS: Suspension-feeding bivalves · Phytoplankton · Nutrient cycling · Carrying capacity · Thau lagoonResale or republication not permitted without written consent of the publisher

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Section: Discussionmentioning

confidence: 99%

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

Souchu

Vaquer²,

Collos³

et al. 2001

Mar. Ecol. Prog. Ser.

148

108

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“…This tiny unicellular green alga belongs to the Prasinophyceae, one of the most ancient groups (2) within the lineage giving rise to the green plants currently dominating terrestrial photosynthesis (the green lineage) (3,4). Consequently, since its discovery, there has been great interest in O. tauri, which, because of its apparent overall simplicity, a naked, nonflagellated cell possessing a single mitochondrion and chloroplast, in addition to its small size and ease in culturing, renders it an excellent model organism (5). Furthermore, it has been hypothesized, based on its small cellular and genome sizes (2,6), that it may reveal the ''bare limits'' of life as a free-living photosynthetic eukaryote, presumably having disposed of redundancies and presenting a simple organization and very little noncoding sequence.…”

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confidence: 99%

Genome analysis of the smallest free-living eukaryote Ostreococcus tauri unveils many unique features

Derelle

Ferraz

Rombauts

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

812

703

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The green lineage is reportedly 1,500 million years old, evolving shortly after the endosymbiosis event that gave rise to early photosynthetic eukaryotes. In this study, we unveil the complete genome sequence of an ancient member of this lineage, the unicellular green alga Ostreococcus tauri (Prasinophyceae). This cosmopolitan marine primary producer is the world's smallest free-living eukaryote known to date. Features likely reflecting optimization of environmentally relevant pathways, including resource acquisition, unusual photosynthesis apparatus, and genes potentially involved in C4 photosynthesis, were observed, as was downsizing of many gene families. Overall, the 12.56-Mb nuclear genome has an extremely high gene density, in part because of extensive reduction of intergenic regions and other forms of compaction such as gene fusion. However, the genome is structurally complex. It exhibits previously unobserved levels of heterogeneity for a eukaryote. Two chromosomes differ structurally from the other eighteen. Both have a significantly biased G؉C content, and, remarkably, they contain the majority of transposable elements. Many chromosome 2 genes also have unique codon usage and splicing, but phylogenetic analysis and composition do not support alien gene origin. In contrast, most chromosome 19 genes show no similarity to green lineage genes and a large number of them are specialized in cell surface processes. Taken together, the complete genome sequence, unusual features, and downsized gene families, make O. tauri an ideal model system for research on eukaryotic genome evolution, including chromosome specialization and green lineage ancestry.genome heterogeneity ͉ genome sequence ͉ green alga ͉ Prasinophyceae ͉ gene prediction

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“…Within this size class, the smallest known eukaryotes are Ostreococcus tauri and related species. Although more similar to flattened spheres in shape, these organisms are Ϸ1 m in diameter (3,4) and have been isolated or detected from samples of diverse geographical origins (5)(6)(7)(8). They belong to the Prasinophyceae, an early diverging class within the green plant lineage, and have a strikingly simple cellular organization, with no cell wall or flagella, and with a single chloroplast and mitochondrion (4).…”

mentioning

confidence: 99%

The tiny eukaryote Ostreococcus provides genomic insights into the paradox of plankton speciation

Palenik

Grimwood

Aerts

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

582

532

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The smallest known eukaryotes, at Ϸ1-m diameter, are Ostreococcus tauri and related species of marine phytoplankton. The genome of Ostreococcus lucimarinus has been completed and compared with that of O. tauri. This comparison reveals surprising differences across orthologous chromosomes in the two species from highly syntenic chromosomes in most cases to chromosomes with almost no similarity. Species divergence in these phytoplankton is occurring through multiple mechanisms acting differently on different chromosomes and likely including acquisition of new genes through horizontal gene transfer. We speculate that this latter process may be involved in altering the cell-surface characteristics of each species. In addition, the genome of O. lucimarinus provides insights into the unique metal metabolism of these organisms, which are predicted to have a large number of selenocysteine-containing proteins. Selenoenzymes are more catalytically active than similar enzymes lacking selenium, and thus the cell may require less of that protein. As reported here, selenoenzymes, novel fusion proteins, and loss of some major protein families including ones associated with chromatin are likely important adaptations for achieving a small cell size.green algae ͉ picoeukaryote ͉ genome evolution ͉ selenium ͉ synteny P hytoplankton living in the oceans perform nearly half of total global photosynthesis (1). Eukaryotic phytoplankton exhibit great diversity that contrasts with the lower apparent diversity of ecological niches available to them in aquatic ecosystems. This observation, know as the ''paradox of the plankton,'' has long puzzled biologists (2). By providing molecular level information on related species, genomics is poised to provide new insights into this paradox.Picophytoplankton, with cell diameters Ͻ2 m, play a significant role in major biogeochemical processes, primary productivity, and food webs, especially in oligotrophic waters. Within this size class, the smallest known eukaryotes are Ostreococcus tauri and related species. Although more similar to flattened spheres in shape, these organisms are Ϸ1 m in diameter (3, 4) and have been isolated or detected from samples of diverse geographical origins (5-8). They belong to the Prasinophyceae, an early diverging class within the green plant lineage, and have a strikingly simple cellular organization, with no cell wall or flagella, and with a single chloroplast and mitochondrion (4). Recent work has shown that small-subunit rDNA sequences of Ostreococcus from cultures and environmental samples cluster into four different clades that are likely distinct enough to represent different species (6, 9).Here we report on the gene content, genome organization, and deduced metabolic capacity of the complete genome of Ostreococcus sp. strain CCE9901 (7), a representative of surface-ocean adapted Ostreococcus, referred to here as Ostreococcus lucimarinus. We compare it to the analogous features of the related species O. tauri strain OTH95 (10). Our results show that many process...

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A new marine picoeucaryote: Ostreococcus tauri gen. et sp. nov. (Chlorophyta, Prasinophyceae)

Cited by 150 publications

References 29 publications

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

Influence of shellfish farming activities on the biogeochemical composition of the water column in Thau lagoon

Genome analysis of the smallest free-living eukaryote Ostreococcus tauri unveils many unique features

The tiny eukaryote Ostreococcus provides genomic insights into the paradox of plankton speciation

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