''Ostreococcus'' is a genus of unicellular coccoid or spherically shaped

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

belonging to the class

Mamiellophyceae Mamiellophyceae is a class of green algae in the division Chlorophyta. The class contains three orders containing 25 species. * Order Dolichomastigales Marin & Melkonian (7 species) * Order Mamiellales Moestrup (13 species) * Order Monomas ...

. It includes prominent members of the global

picoplankton Picoplankton is the fraction of plankton composed by cell (biology), cells between 0.2 and 2 μm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs: * photosynthetic * heterotrophic They are prevalent amongst microbial p ...

community, which plays a central role in the oceanic

carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...

History

The first member of the genus, '' O. tauri'', was discovered in 1994 in an investigation of the picoplankton in the Thau lagoon by Courties and Chretiennot-Dinet using

flow cytometry Flow cytometry (FC) is a technique used to detect and measure the physical and chemical characteristics of a population of cells or particles. In this process, a sample containing cells or particles is suspended in a fluid and injected into the ...

. Unicellular photosynthetic organisms are generally amenable to study using flow cytometry because of the

autofluorescence Autofluorescence is the natural fluorescence of biological structures such as mitochondria and lysosomes, in contrast to fluorescence originating from artificially added fluorescent markers (fluorophores). The most commonly observed autofluoresc ...

provided by

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

and other

fluorophore A fluorophore (or fluorochrome, similarly to a chromophore) is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with se ...

s used by the cells for the harvesting and control of sunlight, which allows such pigments to be studied without any staining of the cells. The different pigments present can be distinguished and identified on a cell-by-cell basis using flow cytometry, allowing researchers to deduce the different species present in the sample and help classify any new species found. ''O. tauri'' was immediately placed in the class

Prasinophyceae The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives.Sym, S. D. and Pienaar, R. N. 1993. The class Prasinophyceae. In Round, F. E. and Chapman ...

based on the presence of characteristic chlorophyll pigments and

Chlorophyceae The Chlorophyceae, also known as chlorophycean algae, are one of the classes of green algae, within the phylum Chlorophyta. They are a large assemblage of mostly freshwater and terrestrial organisms; many members are important primary producers i ...

-related

carotenoids Carotenoids () are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and Fungus, fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips ...

as well as cell ultrastructure, and its position was later confirmed by analysis of its

18S rDNA 18S ribosomal RNA (abbreviated 18S rRNA) is a part of the ribosomal RNA in eukaryotes. It is a component of the Eukaryotic small ribosomal subunit (40S) and the cytosolic homologue of both the 12S rRNA in mitochondria and the 16S rRNA in plastid ...

. Molecular phylogenetic analysis based on the 18S rDNA sequence led the definition of a new class, the Mamiellophyceae, that contains ''Ostreococcus'' species and placed them within the ''Bathycoccaceae'' family. Mamiellophyceae represent one of the ecologically most successful groups of eukaryotic, photosynthetic picoplankters in marine and likely also freshwater environments.

Metagenomic Metagenomics is the study of all genetic material from all organisms in a particular environment, providing insights into their composition, diversity, and functional potential. Metagenomics has allowed researchers to profile the microbial co ...

and

metabarcoding Metabarcoding is the DNA barcoding, barcoding of DNA/RNA (or Environmental DNA, eDNA/Environmental DNA, eRNA) in a manner that allows for the simultaneous identification of many taxa within the same sample. The main difference between barcodin ...

surveys revealed the presence of other members of the genus ''Ostreococcus'' in many oceanic regions. Four different species have been described to date : ''O. tauri'', ''O. lucimarinus'', ''O. mediterraneus'' and ''O spp.'' RCC809.

Anatomy

The genus contains the smallest known free-living

eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

species, with an average size of 0.8 μm. The

ultrastructure Ultrastructure (or ultra-structure) is the architecture of cells and biomaterials that is visible at higher magnifications than found on a standard optical light microscope. This traditionally meant the resolution and magnification range of a c ...

of cells in this genus have so far been characterised by remarkable simplicity, being coccoid cells lacking a

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

and containing a single

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

, a single

mitochondrion A mitochondrion () is an organelle found in the cell (biology), cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosine tri ...

, and a single

Golgi body The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles in ...

as well as its

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

. The genome sequence of three members of this genus is available: the 13 Mb nuclear genome of ''O. tauri'' RCC4221 published in 2006 and updated 2014; ''O. lucimarinus'' CCMP2514 and strain RCC809. The draft metabolic networks of these two ''Ostreococcus'' species were reconstructed from the

KEGG KEGG (Kyoto Encyclopedia of Genes and Genomes) is a collection of databases dealing with genomes, biological pathways, diseases, drugs, and chemical substances. KEGG is utilized for bioinformatics research and education, including data analysis ...

database, thermodynamically constrained, elementally balanced, and functionally evaluated in 2012.

References

{{Taxonbar, from=Q3489010 Chlorophyta genera Mamiellophyceae