Picoeukaryote
Encyclopedia
Picoeukaryotes are picoplankton
ic eukaryotic organisms that range in size from 0.2 – 2.0 µm. They are distributed throughout the world’s marine
and freshwater
ecosystems and constitute a significant contribution to autotroph
ic 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
.
s. For example, Ostreococcus tauri
, an autotrophic picoeukaryote belonging to the class Prasinophyceae
, contains only the nucleus
, one mitochondrion
and one chloroplast
, tightly packed within a cell membrane
. Members of a heterotrophic class, the Bicosoecida, similarly contain only two mitochondria, one food vacuole
and a nucleus.
, they have been found in the vicinity of hydrothermal vents at depths up to 2000-2550 m. Some heterotrophic lineages are found, unstratified, at all depths from the surface down to 3000 m. They show high phylogenetic diversity and high variability in global cell concentrations, ranging from 107 to 105 liter
-1.
(a kind of green algae
) and the Haptophyceae. Regardless of their small size, these organisms have been found to contribute at least 10% of the total global aquatic net primary productivity. In more oligotrophic environments, such as Station ALOHA
, researchers believe that approximately 80% of the chlorophyll
α biomass
is due to cells in the pico
-size range.
Analysis of rDNA
sequences indicate that heterotrophic oceanic picoeukaryotes belong to lineages such as the Alveolata, stramenopiles, choanoflagellates, and Acantharea
. In these lineages, many groups do not have cultured representatives yet. Grazing experiments have demonstrated that novel stramenopile picoeukaryotes are bacterivorous.
(FISH) experiments have shown that picoeukaryotes are fairly abundant in the deep sea
. Increased resolution with the development of better FISH techniques indicates that study and detection should become easier. Research has also shown that picoeukaryotes have a strong correlation with chlorophyll concentrations in both meso-autotrophic reservoirs and hypereutrophic reservoirs. Moreover, nitrogen enrichment experiments suggest that picoeukaryotes have an advantage over larger cells when it comes to acquiring nutrients because of their large surface area per unit volume. They have exhibited more effectiveness in the uptake of photons and nutrient from low-resource environments.
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....
ic eukaryotic organisms that range in size from 0.2 – 2.0 µm. They are distributed throughout the world’s marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
and freshwater
Freshwater
Fresh water is naturally occurring water on the Earth's surface in ice sheets, ice caps, glaciers, bogs, ponds, lakes, rivers and streams, and underground as groundwater in aquifers and underground streams. Fresh water is generally characterized by having low concentrations of dissolved salts and...
ecosystems and constitute a significant contribution to autotroph
Autotroph
An autotroph, or producer, is an organism that produces complex organic compounds from simple inorganic molecules using energy from light or inorganic chemical reactions . They are the producers in a food chain, such as plants on land or algae in water...
ic communities
Community (ecology)
In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...
. Though the SI
Si
Si, si, or SI may refer to :- Measurement, mathematics and science :* International System of Units , the modern international standard version of the metric system...
prefix pico- might imply an organism smaller than atomic size, the term was likely used to avoid confusion with existing size classifications of plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
.
Cell structure
Picoeukaryotes can be either autotrophic and heterotrophic, and usually contain a minimal number of organelleOrganelle
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....
s. For example, Ostreococcus tauri
Ostreococcus
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.-History:...
, an autotrophic picoeukaryote 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...
, contains only the 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...
, one 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 one 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...
, tightly packed within a cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
. Members of a heterotrophic class, the Bicosoecida, similarly contain only two mitochondria, one food vacuole
Vacuole
A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including enzymes in solution, though in certain...
and a nucleus.
Distributions
These organisms are found throughout the water columns. Autotrophic picoeukaryotes are restricted to the upper 100-200 m (the layer that receives light) and are often characterized by a sharp cell maximum near the Deep Chlorophyll Maximum Layer (DCML) and decrease significantly below. Heterotrophic groups are found at greater depths and for example, in the Pacific OceanPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, they have been found in the vicinity of hydrothermal vents at depths up to 2000-2550 m. Some heterotrophic lineages are found, unstratified, at all depths from the surface down to 3000 m. They show high phylogenetic diversity and high variability in global cell concentrations, ranging from 107 to 105 liter
Litér
- External links :*...
-1.
Diversity
Autotrophic picoeukaryotes are members of groups such as the PrasinophyceaePrasinophyceae
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...
(a kind of green algae
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...
) and the Haptophyceae. Regardless of their small size, these organisms have been found to contribute at least 10% of the total global aquatic net primary productivity. In more oligotrophic environments, such as Station ALOHA
Hawaii Ocean Time-series
The Hawaii Ocean Time-series program is a long-term oceanographic study based at the University of Hawaii at Manoa.Scientists working on the Hawaii Ocean Time-series program have been making repeated observations of the hydrography, chemistry and biology of the water column at a station north of...
, researchers believe that approximately 80% of the 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...
α biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
is due to cells in the pico
Pico
Pico- is a prefix in the metric system denoting a factor of 10−12 or .Derived from the Italian piccolo, meaning small, this was one of the original 12 prefixes defined in 1960 when the International System of Units was established....
-size range.
Analysis of rDNA
RDNA
rDNA may stand for:*ribosomal DNA*recombinant DNARDNA is also an acronym for*Reformed Druids of North America...
sequences indicate that heterotrophic oceanic picoeukaryotes belong to lineages such as the Alveolata, stramenopiles, choanoflagellates, and Acantharea
Acantharea
The Acantharea are a group of radiolarian protozoa, distinguished mainly by their skeletons.-Structure:These are composed of strontium sulfate crystals, which do not fossilize, and take the form of either ten diametric or twenty radial spines...
. In these lineages, many groups do not have cultured representatives yet. Grazing experiments have demonstrated that novel stramenopile picoeukaryotes are bacterivorous.
Ecology
Since the size of these organisms determines how they interact with their environment, it is no surprise that they are not known to form significant sinking organic aggregates. Their contribution to carbon cycling is difficult to assess because they are difficult to separate by techniques such as filtration. Recent fluorescent in situ hybridizationFluorescent in situ hybridization
FISH is a cytogenetic technique developed by biomedical researchers in the early 1980s that is used to detect and localize the presence or absence of specific DNA sequences on chromosomes. FISH uses fluorescent probes that bind to only those parts of the chromosome with which they show a high...
(FISH) experiments have shown that picoeukaryotes are fairly abundant in the deep sea
Deep sea
The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...
. Increased resolution with the development of better FISH techniques indicates that study and detection should become easier. Research has also shown that picoeukaryotes have a strong correlation with chlorophyll concentrations in both meso-autotrophic reservoirs and hypereutrophic reservoirs. Moreover, nitrogen enrichment experiments suggest that picoeukaryotes have an advantage over larger cells when it comes to acquiring nutrients because of their large surface area per unit volume. They have exhibited more effectiveness in the uptake of photons and nutrient from low-resource environments.
Biological characteristics
Picoeukaryotes, much like other planktonic species, are exposed to light variations during the diel cycle and due to vertical displacement in the mixed layer of the water column. They have specialized biological reactions to help them deal with excessive densities of light, such as the Xanthophyll cycle.See also
- PhytoplanktonPhytoplanktonPhytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
- BacterioplanktonBacterioplanktonBacterioplankton refers to the bacterial component of the plankton that drifts in the water column. The name comes from the Ancient Greek word , meaning "wanderer" or "drifter" , and , a Latin neologism coined in the 19th century by Christian Gottfried Ehrenberg...
- List of eukaryotic picoplankton species
External links
- MicrobeWiki A site on a biology Wiki run by Kenyon College