Ostreococcus
Encyclopedia
Ostreococcus is a genus of unicellular coccoid
or spherically shaped green alga
belonging to the class Prasinophyceae
. It includes prominent members of the global picoplankton
community, which plays a central role in the oceanic carbon cycle
.
, was discovered in 1994 in an investigation of the picoplankton in the Thau lagoon by Courties and Chretiennot-Dinet using flow cytometry
. Unicellular photosynthetic organisms are generally amenable to study using flow cytometry because of the autofluorescence
provided by chlorophyll
and other fluorophore
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
based on the presence of characteristic chlorophyll pigments and Chlorophyceae
-related carotenoids as well as cell ultrastructure, and its position was later confirmed by analysis of its 18S rDNA. Other members of the genus have since been found in many oceanic regions.
species, with an average size of 0.8 µm. The ultrastructure
of cells in this genus have so far been characterised by remarkable simplicity, being coccoid cells lacking a cell wall
and containing a single chloroplast
, a single mitochondrion
, and a single Golgi body as well as its nucleus
. The genome sequence of three members of this genus have been published: the 12.56 Mb nuclear genome of O. tauri in 2006, and the sequences of O. lucimarinus and strain RCC141 have followed.
Coccus
Coccus can be used to describe any bacterium that has a spherical shape. It is one of the three distinct types of bacteria shapes, the other two being bacillus and spirillum cells...
or spherically shaped green alga
Green algae
The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic...
belonging to the class Prasinophyceae
Prasinophyceae
In taxonomy, Prasinophytes are a class of the Division Chlorophyta. These are primitive eukaryotic, marine green algae. Its best known genus is Ostreococcus , which is considered to be the smallest free-living eukaryote and which has been detected in marine samples around the world...
. It includes prominent members of the global picoplankton
Picoplankton
Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that can be either :* photosynthetic * heterotrophic Some species can also be mixotrophic....
community, which plays a central role in the oceanic carbon cycle
Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth...
.
History
The first member of the genus, O. tauriOstreococcus tauri
Ostreococcus tauri is a unicellular species of green alga about 0.8 micrometres in diameter, the smallest free-living eukaryote yet described. It has a very simple ultrastructure, and a compact genome....
, was discovered in 1994 in an investigation of the picoplankton in the Thau lagoon by Courties and Chretiennot-Dinet using flow cytometry
Flow cytometry
Flow cytometry is a technique for counting and examining microscopic particles, such as cells and chromosomes, by suspending them in a stream of fluid and passing them by an electronic detection apparatus. It allows simultaneous multiparametric analysis of the physical and/or chemical...
. Unicellular photosynthetic organisms are generally amenable to study using flow cytometry because of the autofluorescence
Autofluorescence
Autofluorescence is the natural emission of light by biological entities such as mitochondria and lysosomes, and is used to distinguish the light originating from artificially added fluorescent markers...
provided by chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
and other fluorophore
Fluorophore
A fluorophore, in analogy to a chromophore, is a component of a molecule which causes a molecule to be fluorescent. It is a functional group in a molecule which will absorb energy of a specific wavelength and re-emit energy at a different wavelength...
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
Prasinophyceae
In taxonomy, Prasinophytes are a class of the Division Chlorophyta. These are primitive eukaryotic, marine green algae. Its best known genus is Ostreococcus , which is considered to be the smallest free-living eukaryote and which has been detected in marine samples around the world...
based on the presence of characteristic chlorophyll pigments and Chlorophyceae
Chlorophyceae
The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. For example the chlorophycean CW clade, and chlorophycean DO clade, are defined by the arrangement of their flagella. Members of the CW clade have flagella that are displaced...
-related carotenoids as well as cell ultrastructure, and its position was later confirmed by analysis of its 18S rDNA. Other members of the genus have since been found in many oceanic regions.
Anatomy
The genus contains the smallest known free-living eukaryoticEukaryote
A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...
species, with an average size of 0.8 µm. The ultrastructure
Ultrastructure
Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be observed by electron microscopy...
of cells in this genus have so far been characterised by remarkable simplicity, being coccoid cells lacking a cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
and containing a single chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
, a single mitochondrion
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
, and a single Golgi body as well as its nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
. The genome sequence of three members of this genus have been published: the 12.56 Mb nuclear genome of O. tauri in 2006, and the sequences of O. lucimarinus and strain RCC141 have followed.