| Ostreococcus | |
|---|---|
Scientific classification  | |
| (unranked): | Viridiplantae |
| Division: | Chlorophyta |
| Class: | Mamiellophyceae |
| Order: | Mamiellales |
| Family: | Bathycoccaceae |
| Genus: | Ostreococcus C. Courties & M.-J. Chrétiennot-Dinet (1995) |
| Species | |
Ostreococcus is a genus of unicellular coccoid or spherically shaped green algae belonging to the class Mamiellophyceae. It includes prominent members of the global picoplankton community, which plays a central role in the oceanic carbon cycle.
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. [1] Unicellular photosynthetic organisms are generally amenable to study using flow cytometry because of the autofluorescence provided by chlorophyll and other fluorophores 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. [2] O. tauri was immediately placed in the class Prasinophyceae based on the presence of characteristic chlorophyll pigments and Chlorophyceae-related carotenoids [1] as well as cell ultrastructure, and its position was later confirmed by analysis of its 18S rDNA. [3] Molecular phylogenetic analysis based on the 18SrDNA sequence led the definition of a new class, the Mamiellophyceae, that contains Ostreococcus species and placed them within the Bathycoccaceae family. [4] Mamiellophyceae represent one of the ecologically most successful groups of eukaryotic, photosynthetic picoplankters in marine and likely also freshwater environments. Metagenomic [5] and metabarcoding [6] 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, [7] O. mediterraneus [8] and O spp. RCC809. [9]
The genus contains the smallest known free-living eukaryotic species, with an average size of 0.8 µm. [1] 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. [1] The genome sequence of three members of this genus is available: the 13 Mb nuclear genome of O. tauri RCC4221 published in 2006 [10] and updated 2014; [11] O. lucimarinus CCMP2514 [7] and strain RCC809. [9] The draft metabolic networks of these two Ostreococcus species were reconstructed from the KEGG database, thermodynamically constrained, elementally balanced, and functionally evaluated in 2012. [12]
Charophyta is a group of freshwater green algae, called charophytes, sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged deep within Charophyta, possibly from terrestrial unicellular charophytes, with the class Zygnematophyceae as a sister group.
The Archaeplastida are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It also includes the non-photosynthetic lineage Rhodelphidia, a predatorial (eukaryotrophic) flagellate that is sister to the Rhodophyta, and probably the microscopic picozoans. The Archaeplastida have chloroplasts that are surrounded by two membranes, suggesting that they were acquired directly through a single endosymbiosis event by phagocytosis of a cyanobacterium. All other groups which have chloroplasts, besides the amoeboid genus Paulinella, have chloroplasts surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae. Unlike red and green algae, glaucophytes have never been involved in secondary endosymbiosis events.
Picoplankton is the fraction of plankton composed by cells between 0.2 and 2 μm that can be either prokaryotic and eukaryotic phototrophs and heterotrophs:
Photosynthetic picoplankton or picophytoplankton is the fraction of the photosynthetic phytoplankton of cell sizes between 0.2 and 2 µm. It is especially important in the central oligotrophic regions of the world oceans that have very low concentration of nutrients.
Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm. The photosynthetic coccoid cells are preferentially found in well–lit surface waters where it can be very abundant. Many freshwater species of Synechococcus have also been described.
The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives. The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells. The cells of many species are covered with organic body scales; others are naked. Well studied genera include Ostreococcus, considered to be the smallest free-living eukaryote, and Micromonas, both of which are found in marine waters worldwide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes . At least one species, the Antarctic form Pyramimonas gelidicola, is capable of phagocytosis and is therefore a mixotrophic algae.
Mamiellales are an order of green algae in the class Mamiellophyceae. Their cells and flagella are covered with spiderweb-like scales of several types. Some species lack scales but possess pigments similar to those of the scale-bearing species.
Micromonas is a genus of green algae in the family Mamiellaceae.
Nephroselmis is a genus of green algae. It has been placed in the family Nephroselmidaceae, although a 2009 study suggests that it should be separated into its own class, Nephroselmidophyceae. One species can be an endosymbiont of Hatena arenicola.
Prasinoderma is a genus of green algae in the phylum Prasinodermophyta. Both species in the genus are unicellular, but P. coloniale forms loose sticky colonies.
Trebouxia is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions. It can either exist in a symbiotic relationship with fungi in the form of lichen or it can survive independently as a free-living organism alone or in colonies. Trebouxia is the most common photobiont in extant lichens. It is a primary producer of marine, freshwater and terrestrial ecosystems. It uses carotenoids and chlorophyll a and b to harvest energy from the sun and provide nutrients to various animals and insects.
Picoeukaryotes are picoplanktonic eukaryotic organisms 3.0 µm or less in size. They are distributed throughout the world's marine and freshwater ecosystems and constitute a significant contribution to autotrophic communities. Though the SI prefix pico- might imply an organism smaller than atomic size, the term was likely used to avoid confusion with existing size classifications of plankton.
Red algae, or Rhodophyta, are one of the oldest groups of eukaryotic algae. The Rhodophyta comprises one of the largest phyla of algae, containing over 7,000 currently recognized species with taxonomic revisions ongoing. The majority of species (6,793) are found in the Florideophyceae (class), and mostly consist of multicellular, marine algae, including many notable seaweeds. Red algae are abundant in marine habitats but relatively rare in freshwaters. Approximately 5% of red algae species occur in freshwater environments, with greater concentrations found in warmer areas. Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, there are no terrestrial species, which may be due to an evolutionary bottleneck in which the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity.
Hemiselmis is a genus of cryptomonads.
Nannochloropsis is a genus of algae comprising six known species. The genus in the current taxonomic classification was first termed by Hibberd (1981). The species have mostly been known from the marine environment but also occur in fresh and brackish water. All of the species are small, nonmotile spheres which do not express any distinct morphological features that can be distinguished by either light or electron microscopy. The characterisation is mostly done by rbcL gene and 18S rRNA sequence analysis.
Ostreococcus tauri is a unicellular species of marine green alga about 0.8 micrometres (μm) in diameter, the smallest free-living (non-symbiotic) eukaryote yet described. It has a very simple ultrastructure, and a compact genome.
Prasinovirus is a genus of large double-stranded DNA viruses, in the family Phycodnaviridae that infect phytoplankton in the Prasinophyceae. There are three groups in this genus, including Micromonas pusilla virus SP1, which infects the cosmopolitan photosynthetic flagellate Micromonas pusilla.
Triparma is a genus of unicellular algae in the family Triparmaceae in the order Parmales. They form siliceous plates on the cell surface that aid in identification. Triparma is distinguished by its possession of three shield plates, three triradiate girdle plates, a triradiate girdle plate with notched ends, and a small ventral plate. It was first described by Booth & Marchant in 1987 and the holotype is Triparma columacea.
Aurigamonas is a genus of predatory protists of an unusual cell structure, with two flagella and numerous haptopodia. It is a monotypic genus containing the single species Aurigamonas solis. It is the only genus of the family Aurigamonadidae.
Chrompodellids are a clade of single-celled protists belonging to the Alveolata supergroup. It comprises two different polyphyletic groups of flagellates: the colpodellids, phagotrophic predators, and the chromerids, photosynthetic algae that live as symbionts of corals. These groups were independently discovered and described, but molecular phylogenetic analyses demonstrated that they are intermingled in a clade that is the closest relative to Apicomplexa, and they became collectively known as chrompodellids. Due to the history of their research, they are variously known in biological classification as Chromerida or Colpodellida (ICZN)/Colpodellales (ICN).