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106-473: Pseudo-nitzschia is a marine planktonic diatom genus that accounts for 4.4% of pennate diatoms found worldwide. Some species are capable of producing the neurotoxin domoic acid (DA), which is responsible for the neurological disorder in humans known as amnesic shellfish poisoning (ASP). Currently, 58 species are known, 28 of which have been shown to produce DA. It was originally hypothesized that only dinoflagellates could produce harmful algal toxins, but

212-463: A urea cycle , a feature that they share with animals , although this cycle is used to different metabolic ends in diatoms. The family Rhopalodiaceae also possess a cyanobacterial endosymbiont called a spheroid body. This endosymbiont has lost its photosynthetic properties, but has kept its ability to perform nitrogen fixation , allowing the diatom to fix atmospheric nitrogen . Other diatoms in symbiosis with nitrogen-fixing cyanobacteria are among

318-575: A bacteria-like fashion. Binary fission in organisms can occur in four ways: irregular , longitudinal , transverse , or oblique . For example: Binary fission means "division into two". It is the simplest and most common method of asexual reproduction. Multiple fission at the cellular level occurs in many protists , e.g. sporozoans and algae . The nucleus of the parent cell divides several times by amitosis , producing several nuclei. The cytoplasm then separates, creating multiple daughter cells. Some parasitic, single-celled organisms undergo

424-452: A better understanding of cell wall formation processes, establishing fundamental knowledge which can be used to create models that contextualise current findings and clarify how the process works. The process of building a mineral-based cell wall inside the cell, then exporting it outside, is a massive event that must involve large numbers of genes and their protein products. The act of building and exocytosing this large structural object in

530-436: A brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an invasive species both in the antipodes and in parts of North America . The problem is most frequently recorded from Australia and New Zealand . When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking

636-425: A brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. Cladophora is frequently covered with Cocconeis , an elliptically shaped diatom; Vaucheria

742-414: A complete mitochondrial GS-GOGAT cycle has been hypothesised. Diatoms are mainly photosynthetic; however a few are obligate heterotrophs and can live in the absence of light provided an appropriate organic carbon source is available. Fission (biology) Organisms in the domains of Archaea and Bacteria reproduce with binary fission. This form of asexual reproduction and cell division

848-569: A deadly bloom of Pseudo-nitzschia occurred in 1987 in the bays of Prince Edward Island, Canada, and led to an outbreak of ASP. Over 100 people were affected by this outbreak after consuming contaminated mussels; three people died. Since this event, no additional deaths have been attributed to ASP, though the prevalence of toxic diatoms and DA has increased worldwide. This anomaly is likely due to increased awareness of harmful algal blooms (HABs) and their implications for human and ecosystem health. Blooms have since been characterized in coastal waters and

954-452: A disproportionately important role in the export of carbon from oceanic surface waters (see also the biological pump ). Significantly, they also play a key role in the regulation of the biogeochemical cycle of silicon in the modern ocean. Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands. The use of silicon by diatoms

1060-426: A diverse background in order to identify residues that differentiate function in the silica deposition process. Additionally, the same study found that a number of the regions were conserved within species, likely the base structure of silica transport. These silica transport proteins are unique to diatoms, with no homologs found in other species, such as sponges or rice. The divergence of these silica transport genes

1166-552: A full genome project is underway. Transcriptomes of three species, P. arenysensis, P. delicatissima , and P. multistriata , have been sequenced. The transcriptomes encode between 17,500 and 20,200 proteins. P. multistriata was found to uniquely encode nitric oxide synthase . Recently, transcriptome analysis of P. multiseries was used to identify a four-gene cluster linked to DA biosynthesis. The identification of these genes presents an opportunity to monitor toxic blooms of Pseudo-nitzschia genetically in order to better understand

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1272-454: A functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the metazoans which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not. While often overlooked in photosynthetic organisms,

1378-448: A headache, or as severe as permanent anterograde memory loss, coma, and death. So, monitoring systems and management practices for recreational and commercial fishing are important to ensure the health of marine animals and their predators. Photosynthesis is essential for the production of domoic acid. Periods of darkness or chemical inhibition of photosynthesis has been shown to inhibit toxin production. Additionally, DA production peaks in

1484-583: A high biomass, suggesting growth limitation seems to induce toxicity. The presence of zooplankton has also been shown to affect the toxicity of Pseudo-nitzschia . The presence of copepods was shown to enhance toxin production of P. seriata . This effect appears to be chemically mediated, as it could be induced without physical contact. Pseudo-nitzschia species also appear to respond dramatically to differences in trace metal concentrations, such as iron (Fe) and copper (Cu). In Fe-limited conditions, Pseudo-nitzschia increases DA production by six to 25 times as

1590-474: A key role in the metabolic response of diatoms to prolonged nutrient deprivation. The cycle enables diatoms to respond immediately to the availability of nutrients and recover by increasing their metabolic and growth rates. Diatoms have the ability to enter two distinct resting stages to overcome periods of stress. A resting spore has a great capacity to survive over extended periods of nutrient deprivation. To avoid low nutrient concentrations during stratification,

1696-476: A link between increasing coastal nutrient levels ( eutrophication ) and an increase in Pseudo-nitzschia blooms. Shellfish become contaminated after feeding on toxic Pseudo-nitzschia blooms and can act as a vector to transfer domoic acid to humans upon ingestion. DA acts as a potent glutamate agonist and is responsible for amnesic shellfish poisoning in humans. Effects can be as minor as vomiting, cramps, and

1802-418: A low PPFD, the exponential growth rate approximately halved and the cells were significantly more toxic. While the effect of availability of different nitrogen sources on toxicity has been studied many times, no general rule could be demonstrated for differences in growth and DA production, with the results varying greatly by species. However, toxin production increases when the nitrogen source could not sustain

1908-466: A mass extinction in which roughly 85% of all species perished. Until 1994, the genus was known as Nitzschia , but was changed to Pseudo-nitzschia because of the ability to form chains of overlapping cells, as well as other minor morphological differences. While the genus can be readily recognized using light microscopy , identification of distinct species can require taxonomic expertise and be extremely time-consuming. Species identification in this genus

2014-450: A more complete understanding of cell wall synthesis. Most centric and araphid pennate diatoms are nonmotile , and their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or

2120-428: A much larger cell, which then returns to size-diminishing divisions. The exact mechanism of transferring silica absorbed by the diatom to the cell wall is unknown. Much of the sequencing of diatom genes comes from the search for the mechanism of silica uptake and deposition in nano-scale patterns in the frustule . The most success in this area has come from two species, Thalassiosira pseudonana , which has become

2226-428: A multiple fission-like process to produce numerous daughter cells from a single parent cell. Isolates of the human parasite Blastocystis hominis were observed to begin such a process within 4 to 6 days. Cells of the fish parasite Trypanosoma borreli have also been observed participating in both binary and multiple fission. In the apicomplexans , a phylum of parasitic protists, multiple fission, or schizogony ,

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2332-473: A particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer. Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans. This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into

2438-415: A result of stress. This increase allows them to enhance Fe acquisition needed for metabolic activities, and can have devastating effects. Over fifty species of Pseudo-nitzschia have been described (following WoRMS unless specified): Many species of Pseudo-nitzschia have been shown to produce domoic acid, although not all strains are toxigenic. Diatom A diatom ( Neo-Latin diatoma )

2544-480: A short time period, synched with cell cycle progression, necessitates substantial physical movements within the cell as well as dedication of a significant proportion of the cell's biosynthetic capacities. The first characterisations of the biochemical processes and components involved in diatom silicification were made in the late 1990s. These were followed by insights into how higher order assembly of silica structures might occur. More recent reports describe

2650-559: A toxic bloom. Though shellfish harvest closures are typically based on cells counts of Pseudo-nitzschia present, these cell counts do not always correlate with DA levels. Thus, it is important to understand the other environmental drivers that may lead to higher production of DA. The largest recorded DA event caused by Pseudo-nitzschia took place along the North American west coast in 2015, causing prolonged closures of razor clam, rock crab, and Dungeness crab fisheries. Later in 2015, DA

2756-422: A transitional stage between centric and raphid pennate diatoms, diatoms with a raphe. Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using hydrolytic enzymes to break down the organic algal material. Diatoms are a widespread group and can be found in the oceans , in fresh water , in soils , and on damp surfaces. They are one of

2862-428: A unique silica cell wall known as a frustule made up of two valves called thecae , that typically overlap one another. The biogenic silica composing the cell wall is synthesised intracellularly by the polymerisation of silicic acid monomers . This material is then extruded to the cell exterior and added to the wall. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of

2968-466: A valve and a girdle band that can easily slide underneath each other and expand to increase cell content over the diatoms progression. The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content. The cytoplasmic layer

3074-465: Is remineralized through respiration. Thus, diatoms are one of the main players in this biological carbon pump, which is arguably the most important biological mechanism in the Earth System allowing CO 2 to be removed from the carbon cycle for very long period. A feature of diatoms is the urea cycle , which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have

3180-427: Is a form of asexual reproduction or cloning, where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms , this method of reproduction is usually known as fissiparity . Any splitting of a single population of individuals into discrete parts may be considered fission. A population may undergo fission process for

3286-522: Is a specimen of extant genus Hemiaulus in Late Jurassic aged amber from Thailand. Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. Diatomaceous earth (diatomite) is a collection of diatom shells found in the Earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have

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3392-597: Is also indicative of the structure of the protein evolving from two repeated units composed of five membrane bound segments, which indicates either gene duplication or dimerization . The silica deposition that takes place from the membrane bound vesicle in diatoms has been hypothesized to be a result of the activity of silaffins and long chain polyamines. This Silica Deposition Vesicle (SDV) has been characterized as an acidic compartment fused with Golgi-derived vesicles. These two protein structures have been shown to create sheets of patterned silica in-vivo with irregular pores on

3498-423: Is also used by some organelles within eukaryotic organisms (e.g., mitochondria ). Binary fission results in the reproduction of a living prokaryotic cell (or organelle) by dividing the cell into two parts, each with the potential to grow to the size of the original. The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart,

3604-434: Is any member of a large group comprising several genera of algae , specifically microalgae , found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass : they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of

3710-401: Is asexual by binary fission , during which the diatom divides into two parts, producing two "new" diatoms with identical genes. Each new organism receives one of the two frustules – one larger, the other smaller – possessed by the parent, which is now called the epitheca ; and is used to construct a second, smaller frustule, the hypotheca . The diatom that received the larger frustule becomes

3816-405: Is believed by many researchers to be the key to this ecological success. Raven (1983) noted that, relative to organic cell walls , silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992) found that diatom dominance of mesocosm communities

3922-567: Is believed to have the potential to identify hundreds of species and accurately differentiate between large quantities of related species. Additionally, this technology has been shown to accurately identify toxic phytoplankton even at extremely low concentrations. The lower limit for detection of Pseudo-nitzschia is as low as 500 cells. The nomenclatural history is given in Hasle (1995) and Bates (2000). The physiological distribution, fixation, and recycling center for inorganic carbon and nitrogen plays

4028-598: Is generally rapid, though its speed varies between species. For E. coli , cells typically divide about every 20 minutes at 37 °C. Because the new cells will, in turn, undergo binary fission on their own, the time binary fission requires is also the time the bacterial culture requires to double in the number of cells it contains. This time period can, therefore, be referred to as the doubling time . Some species other than E. coli may have faster or slower doubling times: some strains of Mycobacterium tuberculosis may have doubling times of nearly 100 hours. Bacterial growth

4134-419: Is home to several organelles, like the chloroplasts and mitochondria. Before the centric diatom begins to expand, its nucleus is at the center of one of the valves and begins to move towards the center of the cytoplasmic layer before division is complete. Centric diatoms have a variety of shapes and sizes, depending on from which axis the shell extends, and if spines are present. Diatom cells are contained within

4240-417: Is imperative to determine the potential toxicity of an algal bloom. Optical microscopy identification techniques are inadequate when a large number of samples must be routinely examined, such as is required for a monitoring program for public health. Recently, a DNA-microarray was developed for simultaneous detection of multiple harmful algal bloom species with an emphasis on Pseudo-nitzschia . The total assay

4346-469: Is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy resting spores . Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell metabolism ). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In

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4452-496: Is limited by factors including nutrient availability and available space, so binary fission occurs at much lower rates in bacterial cultures once they enter the stationary phase of growth. Thermoproteota (formerly Crenarchaeota ) possess neither a cell wall nor the FtsZ mechanism. They use a primitive version of the eukaryotic ESCRT -III system (also known as Cdv ) to manipulate the membrane into separating, specifically by coming into

4558-607: Is manifested either as merogony , sporogony , or gametogony . Merogony results in merozoites , which are multiple daughter cells that originate within the same cell membrane; sporogony results in sporozoites , and gametogony results in micro gametes . Green algae can divide into more than two daughter cells. The exact number of daughter cells depends on the species of algae and is an effect of temperature and light. Most species of bacteria primarily undergo binary reproduction. Some species and groups of bacteria may undergo multiple fission as well, sometimes beginning or ending with

4664-442: Is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size. Diatoms can be obtained from multiple sources. Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping barnacles , oyster and other shells. Diatoms are frequently present as

4770-560: Is not clear, but it is speculated that it may be related to communication, camouflage, thermal exchange and/or UV protection. Diatoms build intricate hard but porous cell walls called frustules composed primarily of silica . This siliceous wall can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species. The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half,

4876-403: Is notoriously difficult due to the presence of cryptic species. Similar species are often differentiated by very small differences in the frustule, such as shape, period, and band stria. The direct impacts of species identification on public health make this a serious concern. Toxogenic and nontoxogenic species commonly co-occur; therefore, discrimination between various Pseudo-nitzschia species

4982-422: Is often covered with small forms. Since diatoms form an important part of the food of molluscs , tunicates , and fishes , the alimentary tracts of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to

5088-492: Is primarily asexual by binary fission , with each daughter cell receiving one of the parent’s cell’s two frustules. However, this asexual division results in a size reduction. To restore the cell size of a diatom population, sexual reproduction must occur. Vegetative diploid cells undergo meiosis to produce active and passive gametes. These gametes then fuse to form a zygote, which then develops into an auxospore. Sexual reproduction leads to both an increase in genotypic diversity and

5194-674: Is that they are surrounded by a cell wall made of silica (hydrated silicon dioxide ), called a frustule . These frustules produce structural coloration , prompting them to be described as "jewels of the sea" and "living opals". Movement in diatoms primarily occurs passively as a result of both ocean currents and wind-induced water turbulence ; however, male gametes of centric diatoms have flagella , permitting active movement to seek female gametes. Similar to plants , diatoms convert light energy to chemical energy by photosynthesis , but their chloroplasts were acquired in different ways. Unusually for autotrophic organisms, diatoms possess

5300-541: Is that they have lost their cell wall of silica, making them the only known shell-less diatoms. The study of diatoms is a branch of phycology . Diatoms are classified as eukaryotes , organisms with a nuclear envelope -bound cell nucleus , that separates them from the prokaryotes archaea and bacteria . Diatoms are a type of plankton called phytoplankton , the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes . They comprise an integral component of

5406-522: Is their restrictive and bipartite silica cell wall that causes them to progressively shrink during asexual cell division. At a critically small cell size and under certain conditions, auxosporulation restitutes cell size and prevents clonal death. The entire lifecycles of only a few diatoms have been described and rarely have sexual events been captured in the environment. Most eukaryotes are capable of sexual reproduction involving meiosis . Sexual reproduction appears to be an obligatory phase in

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5512-399: Is usually limited to a gliding motion. In centric diatoms, the small male gametes have one flagellum while the female gametes are large and non-motile ( oogamous ). Conversely, in pennate diatoms both gametes lack flagella ( isogamous ). Certain araphid species, that is pennate diatoms without a raphe (seam), have been documented as anisogamous and are, therefore, considered to represent

5618-575: The biological carbon pump and influence the ocean carbon cycle . The anthropogenic CO 2 emission to the atmosphere (mainly generated by fossil fuel burning and deforestation) is nearly 11 gigatonne carbon (GtC) per year, of which almost 2.5 GtC is taken up by the surface ocean. In surface seawater ( pH 8.1–8.4), bicarbonate ( HCO 3 ) and carbonate ions ( CO 3 ) constitute nearly 90 and <10% of dissolved inorganic carbon (DIC) respectively, while dissolved CO 2 (CO 2 aqueous) contributes <1%. Despite this low level of CO 2 in

5724-399: The carotenoid fucoxanthin . Individuals usually lack flagella , but they are present in male gametes of the centric diatoms and have the usual heterokont structure, including the hairs ( mastigonemes ) characteristic in other groups. Diatoms are often referred as "jewels of the sea" or "living opals" due to their optical properties. The biological function of this structural coloration

5830-403: The hypotheca , is slightly smaller than the other half, the epitheca . Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical. Their distinguishing feature is a hard mineral shell or frustule composed of opal (hydrated, polymerized silicic acid). Diatoms are divided into two groups that are distinguished by the shape of

5936-443: The mitochondria also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under ammonium ( NH 4 ) nutrition compared with nitrate ( NO 3 ) nutrition. First, in diatoms, and likely some other algae, there is a urea cycle. The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by amino acid Catabolism ; like photorespiration ,

6042-406: The periphyton community. Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist. Fossil evidence suggests that diatoms originated during or before the early Jurassic period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms

6148-458: The spring ), their competitive edge and rapid growth rate enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic r-strategists (i.e. those organisms whose ecology is defined by a high growth rate, r ). The freshwater diatom Didymosphenia geminata , commonly known as Didymo, causes severe environmental degradation in water-courses where it blooms, producing large quantities of

6254-422: The zygote . The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve. A defining characteristic of all diatoms

6360-653: The "salt"). Unknowingly, the viewer's confusion captured the essence of diatoms—mineral utilizing plants. It is not clear when it was determined that diatom cell walls are made of silica, but in 1939 a seminal reference characterized the material as silicic acid in a "subcolloidal" state Identification of the main chemical component of the cell wall spurred investigations into how it was made. These investigations have involved, and been propelled by, diverse approaches including, microscopy, chemistry, biochemistry, material characterisation , molecular biology , 'omics , and transgenic approaches. The results from this work have given

6466-550: The "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves, suggests that this takeover began in the Cretaceous (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the Cenozoic (66 Ma to present). The diagram depicts some mechanisms by which marine diatoms contribute to

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6572-763: The Arctic and Antarctic. In North America, they have been documented along the Pacific coast from Canada to California, along the Atlantic Northeast coast of Canada, North Carolina, and the Gulf of Mexico. Various species have been detected in the open ocean as well as gulfs and bays, showing a presence in many diverse environments, including off the coasts of Canada, Portugal, France, Italy, Croatia, Greece, Ireland, Australia, Morocco, Japan, Spain, Tunisia, Namibia, Singapore, Angola, Philippines, Turkey, Ukraine, Argentina, and Uruguay. Given

6678-581: The FtsZ ring. MinE stops the MinCD activity midcell, allowing FtsZ to take over for binary fission. More specifically, the following steps occur: Studies of bacteria made to not produce a cell wall, called L-form bacteria , shows that FtsZ requires a cell wall to work. Little is known about how bacteria that naturally don't grow a cell wall divide, but it is thought to resemble the L-form's budding -like division process of extrusion and separation. Binary fission

6784-425: The ability to grow in colonial chains. These adaptations increase their surface area to volume ratio and drag , allowing them to stay suspended in the water column longer. Individual cells may regulate buoyancy via an ionic pump. Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through a seamlike structure called

6890-484: The cells to move by gliding. Cells are often found in overlapped, stepped colonies, and exhibit collective motility. Pseudo-nitzschia species synthesize their own food through the use of light and nutrients in photosynthesis . The diatoms have a central vacuole to store nutrients for later use and a light-harvesting system to protect themselves against high-intensity light. The diatom lineage may go back 180 to 250 million years ago (Mya). About 65 Mya, diatoms survived

6996-529: The coasts via rivers, and from below via seafloor sediment recycling, weathering, and hydrothermal activity . Although diatoms may have existed since the Triassic , the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean's silicon cycle. Subsequently,

7102-417: The cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges , the former as zooplankton , the latter as sedentary filter-feeders primarily on the continental shelves . Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms. However, the precise timing of

7208-498: The deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species  that are distributed between the two major diatom groups: centrics and pennates. Diatoms are generally 20 to 200 micrometers in size, with a few larger species. Their yellowish-brown chloroplasts , the site of photosynthesis, are typical of heterokonts , having four cell membranes and containing pigments such as

7314-528: The diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, nitrogen or phosphorus nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus). Because of this bloom-and-bust cycle, diatoms are believed to play

7420-450: The dominant components of phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface ( benthic ), or even under damp atmospheric conditions. They are especially important in oceans, where a 2003 study found that they contribute an estimated 45% of

7526-653: The formation of large initial cells through formation of the auxospore. Cells need to be below a species-specific size threshold for the sexual phase to be induced. Many external cues also regulate the initiation, such as day length, irradiance, and temperature. The basic mode of the sexual phase of reproduction appears to be conserved among Pseudo-nitzschia species. Upon mixing two strains of compatible mating type and of appropriate cell size for sexualization, cells align side by side and differentiate into gametangia. One active (+) and one passive (-) gamete are then produced within each gametangium. The active gamete migrates toward

7632-496: The frustule: the centric diatoms and the pennate diatoms . Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces. Centric diatoms are radially symmetric. They are composed of upper and lower valves – epitheca and hypotheca – each consisting of

7738-441: The genera Hemiaulus , Rhizosolenia and Chaetoceros . Dinotoms are diatoms that have become endosymbionts inside dinoflagellates . Research on the dinoflagellates Durinskia baltica and Glenodinium foliaceum has shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimal to no gene loss. The main difference between these and free living diatoms

7844-458: The identification of novel components involved in higher order processes, the dynamics documented through real-time imaging, and the genetic manipulation of silica structure. The approaches established in these recent works provide practical avenues to not only identify the components involved in silica cell wall formation but to elucidate their interactions and spatio-temporal dynamics. This type of holistic understanding will be necessary to achieve

7950-399: The life cycle of diatoms, particularly as cell size decreases with successive vegetative divisions. Sexual reproduction involves production of gametes and the fusion of gametes to form a zygote in which maximal cell size is restored. The signaling that triggers the sexual phase is favored when cells accumulate together, so that the distance between them is reduced and the contacts and/or

8056-480: The like can cause diseases and death in many marine organisms, as well as the humans who consume them. HABs can result in oxygen depletion caused by increased biomass production. However, blooms of Pseudo-nitzschia more commonly cause harm through the production of the toxin DA, which can be transferred to other trophic levels through bioaccumulation. DA can often be detected in shellfish flesh during and immediately following

8162-470: The middle of the two soon-to-be daughter cells. Euryarchaeota use FtsZ like bacteria do. Some organelles in eukaryotic cells reproduce using binary fission. Mitochondrial fission occurs frequently within the cell, even when the cell is not actively undergoing mitosis, and is necessary to regulate the cell's metabolism . All chloroplasts and some mitochondria (not in animals), both organelles derived from endosymbiosis of bacteria, also use FtsZ in

8268-479: The model species, as the whole genome was sequenced and methods for genetic control were established, and Cylindrotheca fusiformis , in which the important silica deposition proteins silaffins were first discovered. Silaffins, sets of polycationic peptides , were found in C. fusiformis cell walls and can generate intricate silica structures. These structures demonstrated pores of sizes characteristic to diatom patterns. When T. pseudonana underwent genome analysis it

8374-470: The ocean and its slow diffusion rate in water, diatoms fix 10–20 GtC annually via photosynthesis thanks to their carbon dioxide concentrating mechanisms , allowing them to sustain marine food chains . In addition, 0.1–1% of this organic material produced in the euphotic layer sinks down as particles, thus transferring the surface carbon toward the deep ocean and sequestering atmospheric CO 2 for thousands of years or longer. The remaining organic matter

8480-588: The open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the thermocline . Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous upwelling ), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during

8586-566: The open-ocean worldwide and have been linked to increasing marine nutrient concentrations, warming ocean temperatures, and bacterial interactions. Pseudo-nitzschia species are bilaterally symmetrical pennate diatoms . Cell walls are made up of elongated silica frustules . The silica wall is fairly dense which leads to negative buoyancy, providing a number of advantages. The wall allows the diatoms to sink to avoid light inhibition or nutrient limitations, as well as to protect against grazing zooplankton. The silica frustules also contribute vastly to

8692-615: The organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara , much of it from the Bodélé Depression , which was once made up of a system of fresh-water lakes. Diatoms are unicellular organisms : they occur either as solitary cells or in colonies , which can take

8798-469: The parental identity is not lost. FtsZ is homologous to β-tubulin , the building block of the microtubule cytoskeleton used during mitosis in eukaryotes. FtsZ is thought to be the first protein to localize to the site of future division in bacteria, and it assembles into a Z ring, anchored by FtsZ-binding proteins and defines the division plane between the two daughter cells. MinC and MinD function together as division inhibitors, blocking formation of

8904-480: The passive partner and conjugates . The zygote is then becomes an auxospore , which has no rigid frustule. Inside the auxospore, a large initial cell is produced. Sexual reproduction appears to occur exclusively in the exponential growth phase and be linked to cell density. Sexualization can only be initiated when a species-specific threshold cell concentration is met. Decreasing the distance to facilitate contact and/or perception of chemical cues between cells triggers

9010-463: The perception of chemical cues is facilitated. An exploration of the genomes of five diatoms and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. Thus a meiotic toolkit appears to be conserved in these six diatom species, indicating a central role of meiosis in diatoms as in other eukaryotes. Diatoms are mostly non-motile ; however, sperm found in some species can be flagellated , though motility

9116-652: The production of spores . The species Metabacterium polyspora , a symbiont of guinea pigs , has been found to produce multiple endospores in each division. Some species of cyanobacteria have also been found to reproduce through multiple fission. Some protozoans reproduce by yet another mechanism of fission called plasmotomy . In this type of fission, a multinucleate adult parent undergoes cytokinesis to form two multinucleate (or coenocytic ) daughter cells. The daughter cells so produced undergo further mitosis. Opalina and Pelomyxa reproduce in this way. Fragmentation in multicellular or colonial organisms

9222-423: The raphe. In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to. Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; mucilage pads, stalks or tubes; amorphous masses of mucilage; or by threads of chitin (polysaccharide), which are secreted through strutted processes of the cell. Reproduction among these organisms

9328-442: The replicated and original chromosomes are separated. The consequence of this asexual method of reproduction is that all the cells are genetically identical, meaning that they have the same genetic material (barring random mutations ). Unlike the processes of mitosis and meiosis used by eukaryotic cells, binary fission takes place without the formation of a spindle apparatus on the cell. Like in mitosis (and unlike in meiosis),

9434-400: The resting spores can settle to the bottom where the nutrient concentration is higher. A resting cell is better able to rapidly respond when nutrients become available again. This is more often observed in freshwater and pennate diatoms like Pseudo-nitzschia . There is contradictory evidence regarding the presence or absence of a resting stage in Pseudo-nitzschia . Among diatoms, reproduction

9540-614: The same size as its parent, but the diatom that received the smaller frustule remains smaller than its parent. This causes the average cell size of this diatom population to decrease. It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size. Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and auxospore formation must occur. Vegetative cells of diatoms are diploid (2N) and so meiosis can take place, producing male and female gametes which then fuse to form

9646-668: The scale of diatom frustules . One hypothesis as to how these proteins work to create complex structure is that residues are conserved within the SDV's, which is unfortunately difficult to identify or observe due to the limited number of diverse sequences available. Though the exact mechanism of the highly uniform deposition of silica is as yet unknown, the Thalassiosira pseudonana genes linked to silaffins are being looked to as targets for genetic control of nanoscale silica deposition. The ability of diatoms to make silica-based cell walls has been

9752-412: The sediment layers of the earth and to the fossil record, which makes them exceptionally useful in increasing understanding of numerous processes such as gauging the degree of climate change. Before sinking to the ocean floor, every atom of silicon that enters the ocean is integrated into the cell wall of a diatom about 40 times. Silica frustules contain a central raphe, which secretes mucilage that allows

9858-409: The sexual phase, indicating that high cell density is favorable for sexual reproduction. Additionally, the onset of sexualization is linked to a significant reduction in growth of the vegetative and parental cells, suggesting that vegetative division is inhibited when the two strains of opposite mating type come in contact. Pseudo-nitzschia multiseries has a genome consisting of 219 megabases (Mb) and

9964-508: The shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 2000 micrometers. In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by asexual multiple fission ; the maximum life span of individual cells is about six days. Diatoms have two distinct shapes: a few ( centric diatoms ) are radially symmetric, while most ( pennate diatoms ) are broadly bilaterally symmetric. The unique feature of diatoms

10070-400: The spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents. In the open ocean,

10176-482: The stationary phase of the growth cycle when cell division is slowed or absent. Production is minimal or nonexistent during the exponential phase, and ceases completely during the death phase of the growth cycle. Many factors have been linked to promotion of DA production, including sufficient light, elevated or decreased pH, and nutrition limitations. In one species, P. cuspidata , a link has been indicated between toxicity and photosynthesis photon flux density (PPFD). At

10282-465: The subject of fascination for centuries. It started with a microscopic observation by an anonymous English country nobleman in 1703, who observed an object that looked like a chain of regular parallelograms and debated whether it was just crystals of salt, or a plant. The viewer decided that it was a plant because the parallelograms didn't separate upon agitation, nor did they vary in appearance when dried or subjected to warm water (in an attempt to dissolve

10388-401: The top in a scum and can be isolated. The diagram shows the major fluxes of silicon in the current ocean. Most biogenic silica in the ocean ( silica produced by biological activity ) comes from diatoms. Diatoms extract dissolved silicic acid from surface waters as they grow, and return it to the water column when they die. Inputs of silicon arrive from above via aeolian dust , from

10494-461: The total oceanic primary production of organic material. However, a more recent 2016 study estimates that the number is closer to 20%. Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically. Planktonic diatoms in freshwater and marine environments typically exhibit a " boom and bust " (or " bloom and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at

10600-402: The toxicity and environmental conditions that cause them. In general, diatoms flourish in nutrient-rich waters with high light penetration. Some species of Pseudo-nitzschia can grow in a broad temperature range (4–20 °C or 39–68 °F), making it possible for them to inhabit a diverse range of habitats. Pseudo-nitzschia species have been observed in all oceans of the world, including

10706-400: The two-halves and grows a smaller half within it. As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore , usually through meiosis and sexual reproduction, but exceptions exist. The auxospore expands in size to give rise to

10812-436: The urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the cytoplasm , and potentially the plastid   and may help to regulate ammonium metabolism. Because of this cycle, marine diatoms, in contrast to chlorophytes , also have acquired a mitochondrial urea transporter and, in fact, based on bioinformatics ,

10918-469: The warming temperatures of ocean water, decreasing sea ice, and increasing light penetration brought on by climate change, it is likely that the season for favorable growth of toxigenic Pseudo-nitzschia species will expand. It is important to continue monitoring Pseudo-nitzschia blooms and their toxicity, particularly in Arctic and Antarctic habitats that may begin to see higher prevalence of these species. Harmful algal blooms (HABs) of Pseudo-nitzschia and

11024-613: Was detected in whales, dolphins, porpoises, seals, and sea lions. This bloom was dominated by P. australis and likely caused by anomalous warm water and nutrients brought to the surface by upwelling conditions. Prior to this 2015 bloom, the largest Pseudo-nitzschia bloom recorded occurred in September 2004 off the northwest coast of the United States. The maximum cell densities during this bloom reached 13 x 10 cells per liter, with domoic acid levels of 1.3 pg DA/cell. Sediment cores indicate

11130-399: Was directly related to the availability of silicic acid – when concentrations were greater than 2 μmol m , they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers have suggested that the biogenic silica in diatom cell walls acts as an effective pH buffering agent , facilitating the conversion of bicarbonate to dissolved CO 2 (which

11236-505: Was found that it encoded a urea cycle , including a higher number of polyamines than most genomes, as well as three distinct silica transport genes. In a phylogenetic study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species. This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms. The sequences compared in this study were used to create

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