| Oxyrrhis marina | |
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| Species: | O. marina |
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| Oxyrrhis marina Dujardin, 1841 | |
Oxyrrhis marina is a species of heterotrophic dinoflagellate with flagella that is widely distributed in the world's oceans.
This protozoan species has an asymmetrical oval shape to its single-celled body. [1] It has been likened to a rugby ball. [2] The cell usually measures between 20 and 30 micrometers, but it is known to reach 60. It has two flagella with a protruding, tentacle-like bulge between them. The flagella are covered in scales. Most individuals have scales on the body surface, as well. The two flagella have separate functions. One undulates in waves and the other is coiled, producing a corkscrew-like propulsion to move the cell. The individual appears colorless, but a concentrated culture of cells may have a pink tinge. [1]
The species is thought to have a global distribution except for the polar seas, where it is likely absent or rare, though few samples have been taken of these waters. [3] There are specific records from waters near Europe, North America, Asia, New Zealand, the Canary Islands, [4] Hawaii, and the Azores. It has been found in isolated inland waters, as well, such as a lake in Ukraine. It is less common in the open waters of the oceans. There is a question as to how it came to inhabit so many islands if it is apparently rare in the open ocean. It may have been slowly dispersed on the currents, carried in mats of algae, or transported by humans when shipping arose. [3]
It is most common in the intertidal zone and other coastal regions, [3] where it is a member of the plankton. [5] Habitat types include tide pools and estuaries. [6] It was first described from a salt marsh. [3] It tolerates wide ranges in salinity, temperature, and pH. [7]
It is heterotrophic, obtaining nutrients externally instead of synthesizing them by an internal process such as photosynthesis. It is an omnivorous grazer, consuming various types of tiny organisms from its environment. It eats phytoplankton such as minute algaes. [8] It has been observed eating Nannochloris oculata and Micromonas pusilla , other flagellates such as Goniomonas amphinema , Pfiesteria piscicida , and Stoeckeria algicida , and some bacteria. [9] It often eats the coccolithophore Cricosphaera elongata , and, in experimental situations, readily eats Tetraselmis suecica , Isochrysis galbana , and Rhodomonas sp. Some of these food items are relatively large, as large as the O. marina cell itself. It is selective in its grazing, showing clear preferences for certain food taxa. [8] It can also pick certain individuals over others, as evidenced by its preference for virus-infected Emiliana huxleyi cells over healthy cells. [10] It is cannibalistic, as well. It feeds by phagocytosis, totally engulfing its prey. It has been observed spinning one of its flagella in such a way that it creates a current, pulling the item closer so it can seize it. It is also raptorial, approaching and pouncing on the prey item, especially when the item is a protist. [9] O. marina can sense and respond to certain chemicals that are exuded by algal prey. [10]
The locomotion of the O. marina cell is helical due to the simultaneous movement of its two flagella. It mostly swims in a straight line, but it makes turns when it detects food. [11]
In terms of reproduction, O. marina is isogamous, with reproductive cells smaller than the body cell, but very little is known about these. [5]
This species sometimes forms red tides, [3] [5] but will also feed on the raphidophyte, Heterosigma akashiwo , another organism responsible for red tides. [12] Its blooms when forming red tides are likely stimulated by environmental factors, such as drops in salinity or increases in prey abundance. [5] O. marina may also affect the environment by producing dimethyl sulfide, which is released when it grazes on some prey types, such as E. huxleyi. [10]
Predators of O. marina include protozoa such as the ciliate Strombidinopsis jeokjo , copepods such as Acartia tonsa [10] and rotifers. The mixotrophic flagellate Prymnesium parvum is a prey item for O. marina when the former is nutrient-replete, but can become a predator when it is nutrient-stressed [13] It has been used as food for fish larvae, including those of black porgy (Mylio macrocephalus), lemonpeel angelfish (Centropyge flavissima), and grey mullet (Mugil cephalus). Bryozoans have been grown on a mixture of the protist and yeast. [13]
This protist has been studied extensively. It is a model organism for the study of many aspects of protist biology, including feeding behavior, [8] [9] physiology, [1] ecology, [5] [7] growth, [5] trophic position, [7] evolution, genomics, and biogeography. [6] Many more studies of its genetics are now underway. [7] There are some limitations to using the species as a model, in part because dinoflagellates are so diverse. O. marina itself is very diverse, with many varied strains, and their biology is influenced by the environment, so it can be hard to find a representative specimen to use as a model. [14] In fact, some experts deny that it is a dinoflagellate at all, or at least a "true" dinoflagellate. [15] In general, it is still very useful for scientific experiments, and researchers recommend it. [14]
O. marina has genes that have evidently been transferred to it from bacteria. It also has some genes that are related to plastids, indicating that it may have had an ancestor that could perform photosynthesis. Also, it has some genes related to essential amino acid synthesis, something that is uncommon in heterotrophs, as they usually obtain essential amino acids by eating them. [7]
It is easy to isolate from the environment and easy to grow in the laboratory. Cultures are fed Dunaliella primolecta or any of a number of other readily available protists. Dead E. coli cells can also be used for food. It can also be sustained on a nutritional medium. [2] Cultures can be maintained for years. [6]
This protist has been called a morphospecies. As it is now understood, it is composed of a number of isolates, some of which are quite distinct. [1] [3] There are 50 to 80 wild isolates. [2] In the future some of these could be divided into separate taxa, perhaps on the species level. [3] One of these may become Oxyrrhis maritima. Another called O. tenticulifera may be valid, as well. [1]
A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word flagellate also describes a particular construction characteristic of many prokaryotes and eukaryotes and their means of motion. The term presently does not imply any specific relationship or classification of the organisms that possess flagella. However, the term "flagellate" is included in other terms which are more formally characterized.
Coccolithophores, or coccolithophorids, are single-celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the kingdom Protista, according to Robert Whittaker's five-kingdom system, or clade Hacrobia, according to a newer biological classification system. Within the Hacrobia, the coccolithophores are in the phylum or division Haptophyta, class Prymnesiophyceae. Coccolithophores are almost exclusively marine, are photosynthetic, and exist in large numbers throughout the sunlight zone of the ocean.
Zooplankton are the animal component of the planktonic community. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.
The dinoflagellates are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered algae. Dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations vary with sea surface temperature, salinity, and depth. Many dinoflagellates are photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey.
Coccoliths are individual plates or scales of calcium carbonate formed by coccolithophores and cover the cell surface arranged in the form of a spherical shell, called a coccosphere.
Perkinsus marinus is a species of alveolate belonging to the phylum Perkinsozoa. It is similar to a dinoflagellate. It is known as a prevalent pathogen of oysters, causing massive mortality in oyster populations. The disease it causes is known as dermo or perkinsosis, and is characterized by the degradation of oyster tissues. The genome of this species has been sequenced.
Noctiluca scintillans is a marine species of dinoflagellate that can exist in a green or red form, depending on the pigmentation in its vacuoles. It can be found worldwide, but its geographical distribution varies depending on whether it is green or red. This unicellular microorganism is known for its ability to bioluminesce, giving the water a bright blue glow seen at night. However, blooms of this species can be responsible for environmental hazards, such as toxic red tides. They may also be an indicator of anthropogenic eutrophication.
Stephanopogon is a genus of flagellated marine protist that superficially resembles a ciliate.
Phycodnaviridae is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid. As of 2014, there were 33 species in this family, divided among 6 genera. This family belongs to a super-group of large viruses known as nucleocytoplasmic large DNA viruses. Evidence was published in 2014 suggesting that specific strains of Phycodnaviridae might infect humans rather than just algal species, as was previously believed. Most genera under this family enter the host cell by cell receptor endocytosis and replicate in the nucleus. Phycodnaviridae play important ecological roles by regulating the growth and productivity of their algal hosts. Algal species such Heterosigma akashiwo and the genus Chrysochromulina can form dense blooms which can be damaging to fisheries, resulting in losses in the aquaculture industry. Heterosigma akashiwo virus (HaV) has been suggested for use as a microbial agent to prevent the recurrence of toxic red tides produced by this algal species. Phycodnaviridae cause death and lysis of freshwater and marine algal species, liberating organic carbon, nitrogen and phosphorus into the water, providing nutrients for the microbial loop.
Predatory dinoflagellates are predatory heterotrophic or mixotrophic alveolates that derive some or most of their nutrients from digesting other organisms. About one half of dinoflagellates lack photosynthetic pigments and specialize in consuming other eukaryotic cells, and even photosynthetic forms are often predatory.
A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton. There are two types of eukaryotic mixotrophs: those with their own chloroplasts, and those with endosymbionts—and those that acquire them through kleptoplasty or through symbiotic associations with prey or enslavement of their organelles.
Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism is any microscopic living organism or virus, that is too small to see with the unaided human eye without magnification. Microorganisms are very diverse. They can be single-celled or multicellular and include bacteria, archaea, viruses and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.
Akashiwo sanguinea is a species of marine dinoflagellates well known for forming blooms that result in red tides. The organism is unarmored (naked). Therefore, it lacks a thick cellulose wall, the theca, common in other genera of dinoflagellates. Reproduction of the phytoplankton species is primarily asexual.
Bacterial morphological plasticity refers to changes in the shape and size that bacterial cells undergo when they encounter stressful environments. Although bacteria have evolved complex molecular strategies to maintain their shape, many are able to alter their shape as a survival strategy in response to protist predators, antibiotics, the immune response, and other threats.
All living cells produce reactive oxygen species (ROS) as a byproduct of metabolism. ROS are reduced oxygen intermediates that include the superoxide radical (O2−) and the hydroxyl radical (OH•), as well as the non-radical species hydrogen peroxide (H2O2). These ROS are important in the normal functioning of cells, playing a role in signal transduction and the expression of transcription factors. However, when present in excess, ROS can cause damage to proteins, lipids and DNA by reacting with these biomolecules to modify or destroy their intended function. As an example, the occurrence of ROS have been linked to the aging process in humans, as well as several other diseases including Alzheimer's, rheumatoid arthritis, Parkinson's, and some cancers. Their potential for damage also makes reactive oxygen species useful in direct protection from invading pathogens, as a defense response to physical injury, and as a mechanism for stopping the spread of bacteria and viruses by inducing programmed cell death.
Polykrikos kofoidii is a species of phagotrophic marine pseudocolonial dinoflagellates that can capture and engulf other protist prey, including the toxic dinoflagellate, Alexandrium tamarense. P. kofoidii is of scientific interest due to its status as a predator of other dinoflagellates, a behavior that is significant in the control of algal blooms. It has a complex life cycle of both vegetative (asexual) and sexual reproduction complicated by its pseudocolonial structure.
Dinoflagellates are eukaryotic plankton, existing in marine and freshwater environments. Previously, dinoflagellates had been grouped into two categories, phagotrophs and phototrophs. Mixotrophs, however include a combination of phagotrophy and phototrophy. Mixotrophic dinoflagellates are a sub-type of planktonic dinoflagellates and are part of the phylum Dinoflagellata. They are flagellated eukaryotes that combine photoautotrophy when light is available, and heterotrophy via phagocytosis. Dinoflagellates are one of the most diverse and numerous species of phytoplankton, second to diatoms.
Polykrikos is one of the genera of family Polykrikaceae that includes athecate pseudocolony-forming dinoflagellates. Polykrikos are characterized by a sophisticated ballistic apparatus, named the nematocyst-taeniocyst complex, which allows species to prey on a variety of organisms. Polykrikos have been found to regulate algal blooms as they feed on toxic dinoflagellates. However, there is also some data available on Polykrikos being toxic to fish.
Neobodo are diverse protists belonging to the eukaryotic supergroup Excavata. They are Kinetoplastids in the subclass Bodonidae. They are small, free-living, heterotrophic flagellates with two flagella of unequal length used to create a propulsive current for feeding. As members of Kinetoplastids, they have an evident kinetoplast There was much confusion and debate within the class Kinetoplastid and subclass Bodonidae regarding the classification of the organism, but finally the new genera Neobodo was proposed by Keith Vickerman. Although they are one of the most common flagellates found in freshwater, they are also able to tolerate saltwater Their ability to alternate between both marine and freshwater environments in many parts of the world give them a “cosmopolitan” character. Due to their relatively microscopic size ranging between 4-12 microns, they are further distinguished as heterotrophic nanoflagellates. This small size ratio limits them as bacterivores that swim around feeding on bacteria attached to surfaces or in aggregates.
Marine protists are defined by their habitat as protists that live in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Life originated as marine single-celled prokaryotes and later evolved into more complex eukaryotes. Eukaryotes are the more developed life forms known as plants, animals, fungi and protists. Protists are the eukaryotes that cannot be classified as plants, fungi or animals. They are mostly single-celled and microscopic. The term protist came into use historically as a term of convenience for eukaryotes that cannot be strictly classified as plants, animals or fungi. They are not a part of modern cladistics because they are paraphyletic.