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''Pseudo-nitzschia'' is a marine planktonic [[diatom]] genus containing some species capable of producing the neurotoxin [[domoic acid]] (DA), which is responsible for the neurological disorder known as [[amnesic shellfish poisoning]] (ASP). It was originally hypothesized that only dinoflagellates could produce harmful algal toxins, but a deadly bloom of Pseudo-nitzschia occurred in 1987 in the bays of Prince Edward Island, Canada, and lead to an outbreak of ASP.<ref name=":0">{{Cite journal|doi = 10.4319/lo.2002.47.2.0515|title = The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschia multiseries and Pseudo-nitzschia australis|last = Maldonado|first = Maria T.|date = 2002|journal = Limnology and Oceanography|pmid = |access-date =|volume=47|pages=515–526}}</ref> Blooms have since been characterized in coastal waters worldwide and have been linked to increasing marine nutrient concentrations.<ref name=":1">{{Cite journal|title = Sedimentological evidence of an increase in Pseudo-nitzschia (Bacillariophyceae)abundance in response to coastal eutrophication|url = http://onlinelibrary.wiley.com/doi/10.4319/lo.2002.47.2.0551/abstract|journal = Limnology and Oceanography|date = 2002-03-01|issn = 1939-5590|pages = 551–558|volume = 47|issue = 2|doi = 10.4319/lo.2002.47.2.0551|first = Michael L.|last = Parsons|first2 = Quay|last2 = Dortch}}</ref>
''Pseudo-nitzschia'' is a marine planktonic [[diatom]] genus containing some species capable of producing the neurotoxin [[domoic acid]] (DA), which is responsible for the neurological disorder known as [[amnesic shellfish poisoning]] (ASP). Currently, there are 46 known species, 19 of which are known to produced DA (see Known Species). It was originally hypothesized that only dinoflagellates could produce harmful algal toxins, but a deadly bloom of Pseudo-nitzschia occurred in 1987 in the bays of Prince Edward Island, Canada, and lead to an outbreak of ASP.<ref name=":0">{{Cite journal|doi = 10.4319/lo.2002.47.2.0515|title = The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschia multiseries and Pseudo-nitzschia australis|last = Maldonado|first = Maria T.|date = 2002|journal = Limnology and Oceanography|pmid = |access-date =|volume=47|pages=515–526}}</ref> Over 100 people were effected by this outbreak after consuming contaminated mussels, three people died.<ref>{{Cite journal|last=Lim|first=Hong-Chang|last2=Leaw|first2=Chui-Pin|last3=Su|first3=Suriyanti Nyun-Pau|last4=Teng|first4=Sing-Tung|last5=Usup|first5=Gires|last6=Mohammad-Noor|first6=Normawaty|last7=Lundholm|first7=Nina|last8=Kotaki|first8=Yuichi|last9=Lim|first9=Po-Teen|date=2012-10-01|title=Morphology and Molecular Characterization of Pseudo-Nitzschia (bacillariophyceae) from Malaysian Borneo, Including the New Species Pseudo-Nitzschia Circumpora Sp. Nov|url=http://onlinelibrary.wiley.com/doi/10.1111/j.1529-8817.2012.01213.x/abstract|journal=Journal of Phycology|language=en|volume=48|issue=5|pages=1232–1247|doi=10.1111/j.1529-8817.2012.01213.x|issn=1529-8817}}</ref> Blooms have since been characterized in coastal waters worldwide and have been linked to increasing marine nutrient concentrations.<ref name=":1">{{Cite journal|title = Sedimentological evidence of an increase in Pseudo-nitzschia (Bacillariophyceae)abundance in response to coastal eutrophication|url = http://onlinelibrary.wiley.com/doi/10.4319/lo.2002.47.2.0551/abstract|journal = Limnology and Oceanography|date = 2002-03-01|issn = 1939-5590|pages = 551–558|volume = 47|issue = 2|doi = 10.4319/lo.2002.47.2.0551|first = Michael L.|last = Parsons|first2 = Quay|last2 = Dortch}}</ref>


== Morphology and Physiology ==
== Morphology and Physiology ==
''Pseudo-nitzschia'' are bilaterally symmetrical [[Pennate diatom|pennate]] diatoms. Cell walls are made up of elongated silica [[Frustule|frustules]]. This dense silica wall leads to negative buoyancy, which can provide a number of advantages. This wall allows the diatoms to sink in order to avoid light inhibition or nutrient limitations as well as to protect against grazing zooplankton. These silica frustules also  contribute vastly to the sediment layers of the earth as well as to the fossil record. The contribution of diatoms to the fossil record makes them particularly useful in increasing understanding of various processes such as evaluating the degree of climate change. <ref name=":4">{{Cite book|url=http://link.springer.com/chapter/10.1007/978-4-431-55130-0_10|title=Ecology and Evolution of Marine Diatoms and Parmales|last=Kuwata|first=Akira|last2=Jewson|first2=David H.|date=2015-01-01|publisher=Springer Japan|isbn=9784431551294|editor-last=Ohtsuka|editor-first=Susumu|pages=251–275|language=en|doi=10.1007/978-4-431-55130-0_10#page-1|editor-last2=Suzaki|editor-first2=Toshinobu|editor-last3=Horiguchi|editor-first3=Takeo|editor-last4=Suzuki|editor-first4=Noritoshi|editor-last5=Not|editor-first5=Fabrice}}</ref> It has been found that every atom of silicon that enters the ocean is incorporated into a diatom cell wall approximately 40 times before finally sinking to the sea floor.
⚫
''Pseudo-nitzschia'' are bilaterally symmetrical pennate diatoms. Cell walls are made up of elongated silica frustules and contain a central raphe, which secretes mucilage that allows the cells to move by gliding.<ref name=":2">{{Cite journal|title = The marine diatom ''Pseudo-nitzschia galaxiae'' sp. nov. (Bacillariophyceae): morphology and phylogenetic relationships|url = http://phycologia.org/doi/pdf/10.2216/i0031-8884-41-6-594.1|journal = Phycologia|pages = 594–605|volume = 41|issue = 6|doi = 10.2216/i0031-8884-41-6-594.1|first = Nina|last = Lundholm|first2 = Øjvind|last2 = Moestrup}}</ref> Cells are often found in overlapped, stepped colonies and exhibit collective motility.<ref name=":2" /> Species reproduction is often asexual and results in the size reduction of cells. They then undergo sexual reproduction to revert to their original size.<ref name=":3">{{Cite journal|url = |title = Bloom dynamics and physiology of domoic-acid-producing ''Pseudo-nitzschia'' species|last = Bates|first = Stephen|date = 1998|journal = Physiological Ecology of Harmfull Algal Blooms|doi = |pmid = |access-date = }}</ref><ref>Davidovich, N.A. and S.S. Bates. 1998. Sexual reproduction in the pennate diatoms ''Pseudo-nitzschia multiseries'' and ''P. pseudodelicatissima'' (Bacillariophyceae). J. Phycol. 34: 126-137. [http://onlinelibrary.wiley.com/doi/10.1046/j.1529-8817.1998.340126.x/abstract]</ref> ''Pseudo-nitzschia'' are autotrophic organisms meaning they synthesize their own food through the use of light and nutrients in photosynthesis.

⚫
Silica frustules contain a central raphe, which secretes mucilage that allows the cells to move by gliding.<ref name=":2">{{Cite journal|title = The marine diatom ''Pseudo-nitzschia galaxiae'' sp. nov. (Bacillariophyceae): morphology and phylogenetic relationships|url = http://phycologia.org/doi/pdf/10.2216/i0031-8884-41-6-594.1|journal = Phycologia|pages = 594–605|volume = 41|issue = 6|doi = 10.2216/i0031-8884-41-6-594.1|first = Nina|last = Lundholm|first2 = Øjvind|last2 = Moestrup}}</ref> Cells are often found in overlapped, stepped colonies and exhibit collective motility.<ref name=":2" /> ''Pseudo-nitzschia'' are [[Autotroph|autotrophic]] organisms meaning they synthesize their own food through the use of light and nutrients in [[photosynthesis]].These diatoms has a central [[vacuole]] to store nutrients for later use and a light harvesting system to protect itself against high intensity light.<ref name=":4" />


== Taxonomy ==
== Taxonomy ==
Up 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.<ref>Hasle, G.R. 1994. ''Pseudo-nitzschia'' as a genus distinct from ''Nitzschia'' (Bacillariophyceae). J. Phycol. 30: 1036-1039. [http://onlinelibrary.wiley.com/doi/10.1111/j.0022-3646.1994.01036.x/abstract]</ref> The nomenclatural history is given in Hasle (1995)<ref>Hasle, G.R. 1995. ''Pseudo-nitzschia pungens'' and ''P. multiseries'' (Bacillariophyceae): nomenclatural history, morphology, and distribution. J. Phycol. 31: 428-435. [http://onlinelibrary.wiley.com/doi/10.1111/j.0022-3646.1995.00428.x/abstract]</ref> and Bates (2000).<ref>Bates, S.S. 2000. Domoic-acid-producing diatoms: another genus added! J. Phycol. 36: 978-983. [http://onlinelibrary.wiley.com/doi/10.1046/j.1529-8817.2000.03661.x/abstract]</ref>
Diatom lineage may go back 180 to 250 Myr. About 65 Myr ago, diatoms survived the mass extinction that saw the loss of about 85% of all species.<ref name=":4" /> Up 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.<ref>Hasle, G.R. 1994. ''Pseudo-nitzschia'' as a genus distinct from ''Nitzschia'' (Bacillariophyceae). J. Phycol. 30: 1036-1039. [http://onlinelibrary.wiley.com/doi/10.1111/j.0022-3646.1994.01036.x/abstract]</ref> While the genus can be readily recognized using [[Light microscope|LM]], identification of distinct species can require taxonomic expertise and be extremely time consuming. Species identification of this genus 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.<ref>Lim, H.-C., Leaw, C.-P., Su, S. N.-P., Teng, S.-T., Usup, G., Mohammad-Noor, N., Lundholm, N., Kotaki, Y. and Lim, P.-T. (2012), MORPHOLOGY AND MOLECULAR CHARACTERIZATION OF''PSEUDO-NITZSCHIA'' (BACILLARIOPHYCEAE) FROM MALAYSIAN BORNEO, INCLUDING THE NEW SPECIES ''PSEUDO-NITZSCHIA CIRCUMPORA'' SP. NOV. Journal of Phycology, 48: 1232–1247. doi: 10.1111/j.1529-8817.2012.01213.x</ref>

This is a challenging concern because of the direct impacts on pubic health. It is common for toxogenic and non-toxogenic species to co-occur. Therefore, it is crucial to be able to discriminate between various ''Pseudo-nitzschia'' species in order to evaluate a potentially toxic 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 new DNA-microarray was developed for simultaneous detection of multiple Harmful Algal Bloom species with an emphasis on ''Pseudo-nitzschia''. The total assay is is believed to have the potential to identify hundreds of species and differentiate between a large number 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. <ref>{{Cite journal|last=Noyer|first=Charlotte|last2=Abot|first2=Anne|last3=Trouilh|first3=Lidwine|last4=Leberre|first4=Véronique Anton|last5=Dreanno|first5=Catherine|date=2015-05-01|title=Phytochip: Development of a DNA-microarray for rapid and accurate identification of Pseudo-nitzschia spp and other harmful algal species|url=http://www.sciencedirect.com/science/article/pii/S0167701215000810|journal=Journal of Microbiological Methods|volume=112|pages=55–66|doi=10.1016/j.mimet.2015.03.002}}</ref>

The nomenclatural history is given in Hasle (1995)<ref>Hasle, G.R. 1995. ''Pseudo-nitzschia pungens'' and ''P. multiseries'' (Bacillariophyceae): nomenclatural history, morphology, and distribution. J. Phycol. 31: 428-435. [http://onlinelibrary.wiley.com/doi/10.1111/j.0022-3646.1995.00428.x/abstract]</ref> and Bates (2000).<ref>Bates, S.S. 2000. Domoic-acid-producing diatoms: another genus added! J. Phycol. 36: 978-983. [http://onlinelibrary.wiley.com/doi/10.1046/j.1529-8817.2000.03661.x/abstract]</ref>

== Life Cycle ==

=== Ornithine-urea Cycle ===
Physiological distribution and repackaging hub for inorganic carbon and nitrogen and contributes to the metabolic response of diatoms to episodic nitrogen availability. This cycle enables them to respond quickly and recover from prolonged periods of nutrient deprivation so they can rapidly proliferate. <ref name=":4" />

=== Resting Stages ===
Diatoms have the ability to enter two distinct resting stages in order to overcome periods of stress. A resting spore has a great capacity to survive over extended periods of nutrient deprivation. These morphologically distinct resting spores can settle to the bottom, where the nutrient concentration is higher, in order to avoid low nutrient concentrations during stratification. A resting cell is better able to rapidly respond when nutrients become available again. The is more often observed in freshwater and pennate diatoms like ''Pseudo-nitzschia''.<ref name=":4" /> 

=== Reproduction ===
Among diatoms, reproduction is primarily asexual by [[Fission (biology)|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. In order 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 is an important phase in the life cycle of diatoms, and the basic mode of the sexual phase of reproduction appears to be conserved among ''Pseudo-nitzschia species.''<ref name=":5">{{Cite journal|last=Scalco|first=Eleonora|last2=Amato|first2=Alberto|last3=Ferrante|first3=Maria Immacolata|last4=Montresor|first4=Marina|date=2015-10-22|title=The sexual phase of the diatom Pseudo-nitzschia multistriata: cytological and time-lapse cinematography characterization|url=http://link.springer.com/article/10.1007/s00709-015-0891-5|journal=Protoplasma|language=en|pages=1–11|doi=10.1007/s00709-015-0891-5|issn=0033-183X}}</ref> Sexual reproduction leads to both production of genotypic diversity and formation of large sized initial cells through formation of  the auxospore. The sexual phase can be induced only in cells below a species-specific size threshold, however this is not the sole requirement. Many external cues also regulate the process in many diatoms, such as day length, irradiance and temperature. <ref name=":6">{{Cite journal|last=Scalco|first=Eleonora|last2=Stec|first2=Krzysztof|last3=Iudicone|first3=Daniele|last4=Ferrante|first4=Maria Immacolata|last5=Montresor|first5=Marina|date=2014-10-01|title=The dynamics of sexual phase in the marine diatom Pseudo-nitzschia multistriata (Bacillariophyceae)|url=http://onlinelibrary.wiley.com/doi/10.1111/jpy.12225/abstract|journal=Journal of Phycology|language=en|volume=50|issue=5|pages=817–828|doi=10.1111/jpy.12225|issn=1529-8817}}</ref>

Upon mixing two strains of compatible mating type and of appropriate cell size for sexualization, some cells will align side by side and differentiate into gametangia. Two gametes are then produced within each gametangium, one active (+) and one passive (-). The active gamete migrates toward the passive partner and [[Bacterial conjugation|conjugate]]<nowiki/>s. The zygote is then transformed into an auxospore, which has no rigid frustule. Within the auxospore, a large initial cell is produced.<ref name=":5" />

Sexual reproduction appears to be restricted to the exponential growth phase and linked to cell density. A threshold cell concentration is required for commencement of sexualization. This concentration appears to vary by strain. Overall, reducing the distance and facilitating contact and/or perception of chemical cues between cells triggers the sexual phase, suggesting that cell accumulation is favorable for sexual reproduction. Additionally, the onset of the sexual phase 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.<ref name=":6" />

== Genome ==
Very few species of ''Pseudo-nitzschia'' have had their genomes fully sequenced.

''Pseudo-nitzschia multiseries'' has a genome consisting of 300 megabases (Mb).<ref>{{Cite journal|last=Armbrust|first=E. Virginia|date=2009-05-14|title=The life of diatoms in the world's oceans|url=http://www.nature.com/nature/journal/v459/n7244/abs/nature08057.html|journal=Nature|language=en|volume=459|issue=7244|pages=185–192|doi=10.1038/nature08057|issn=0028-0836}}</ref> 

=== Transcriptome ===
The sequencing of diatom genomes showed that this relatively recent eukaryotic lineage harbors a combination of genes and metabolic pathways first thought to be exclusive to plants and animals. Diatoms have the urea cycle and the ability to generate chemical energy from the breakdown of lipids that were considered distinctive animal features. Additionally, have the C4 photosynthetic pathway that was recorded only in some plants.<ref name=":7">Dato, Valeria Di, Francesco Musacchia, Giuseppe Petrosino, Shrikant Patil, Marina Montresor, Remo Sanges, and Maria Immacolata Ferrante. "Transcriptome Sequencing of Three Pseudo-nitzschia Species Reveals Comparable Gene Sets and the Presence of Nitric Oxide Synthase Genes in Diatoms." Sci. Rep. Scientific Reports 5 (2015): 12329. Web.
</ref>

Transcriptome sequences of of species of ''Pseudo-notzschia'' range from 34 million to 118 million.<ref name=":7" />

== Habitat ==
Harmful algal blooms of ''Pseudo-nitzschia'' can be found in coastal regions worldwide. 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.<ref>{{Cite web|url=http://products.coastalscience.noaa.gov/pmn/_docs/Factsheets/Factsheet_Pseudonitzschia.pdf|title=NOAA Coastal Science|last=|first=|date=|website=|publisher=|accessdate=}}</ref> Recently, this genus of diatom has been detected in the open ocean as well as gulfs and bays, showing a presence in many diverse environemnts, including off the coasts of Canada, Portugal, France, Italy, Coratia, Greece, Ireland and Australia.<ref name=":8">{{Cite journal|last=Dhar|first=Bidhan Chandra|last2=Cimarelli|first2=Lucia|last3=Singh|first3=Kumar Saurabh|last4=Brandi|first4=Letizia|last5=Brandi|first5=Anna|last6=Puccinelli|first6=Camilla|last7=Marcheggiani|first7=Stefania|last8=Spurio|first8=Roberto|date=2015-05-06|title=Molecular Detection of a Potentially Toxic Diatom Species|url=http://www.mdpi.com/1660-4601/12/5/4921|journal=International Journal of Environmental Research and Public Health|language=en|volume=12|issue=5|pages=4921–4941|doi=10.3390/ijerph120504921|pmc=4454946|pmid=25955528}}</ref> In general, diatoms thrive in relatively turbulent, nutrient-rich waters.<ref name=":4" /> 


== Harmful Bloom Dynamics ==
== Harmful Bloom Dynamics ==
Harmful algal blooms (HABs) like ''Pseudo-nitzschia'' can be responsible for diseases and death of many marine creatures, as well as the humans that consume them. These negative impacts can occur through four main mechanisms: (i) oxygen depletion resulting from high biomass production; (ii) toxins, like DA, which can be transferred to humans; (iii) physical damage to skin and mucous membranes due to gill irritation or clogging due to sharp and needle-shaped diatoms; and (iv) gas bubble traumas caused by oxygen supersaturation form the high levels of photosynthetic activity.<ref>{{Cite journal|last=Delegrange|first=A.|last2=Vincent|first2=D.|last3=Courcot|first3=L.|last4=Amara|first4=R.|date=2015-02-01|title=Testing the vulnerability of juvenile sea bass (Dicentrarchus labrax) exposed to the harmful algal bloom (HAB) species Pseudo-nitzschia delicatissima|url=http://www.sciencedirect.com/science/article/pii/S0044848614005973|journal=Aquaculture|volume=437|pages=167–174|doi=10.1016/j.aquaculture.2014.11.023}}</ref>
Harmful algal blooms of ''Pseudo-nitzschia'' can be found in coastal regions worldwide. 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.<ref>{{Cite web|url = http://products.coastalscience.noaa.gov/pmn/_docs/Factsheets/Factsheet_Pseudonitzschia.pdf|title = NOAA Coastal Science|date = |accessdate = |website = |publisher = |last = |first = }}</ref> Unlike certain dinoflagellate blooms, domoic-acid-producing ''Pseudo-nitzschia'' species must be present in high concentrations (greater than 100,000 cells L<sup>−1</sup>) in order to contaminate shellfish at a level that would cease harvesting.<ref name=":3" /> Shellfish become contaminated after feeding on these toxic ''Pseudo-nitzschia'' blooms and they can act as a vector that transfers the domoic acid to humans if ingested.<ref>{{Cite web|title = Pseudo-nitzschia toxins|url = http://www.mbari.org/staff/conn/botany/diatoms/jennifer/toxin.htm|website = www.mbari.org|accessdate = 2015-10-29}}</ref> This often leads to ASP in humans, which can have debilitating effects such as permanent short-term memory loss.<ref name=":0" />

Unlike certain dinoflagellate blooms, domoic-acid-producing ''Pseudo-nitzschia'' species must be present in high concentrations (greater than 100,000 cells L<sup>−1</sup>) in order to contaminate shellfish at a level that would cease harvesting.<ref name=":3">{{Cite journal|last=Bates|first=Stephen|date=1998|title=Bloom dynamics and physiology of domoic-acid-producing ''Pseudo-nitzschia'' species|url=|journal=Physiological Ecology of Harmfull Algal Blooms|doi=|pmid=|access-date=}}</ref>

The largest ''pseudo-nitzschia'' bloom on record occurred in September of 2004 off the coast of Washington state and British Columbia. The domoic acid levels reached 1.3 pg DA / cell and the maximum cell densities reached 13 x 10^6 cells / L.<ref name=":9">{{Cite journal|last=Auro|first=Maureen E.|last2=Cochlan|first2=William P.|date=2013-02-01|title=Nitrogen Utilization and Toxin Production by Two Diatoms of the Pseudo-nitzschia pseudodelicatissima Complex: P. cuspidata and P. fryxelliana|url=http://onlinelibrary.wiley.com/doi/10.1111/jpy.12033/abstract|journal=Journal of Phycology|language=en|volume=49|issue=1|pages=156–169|doi=10.1111/jpy.12033|issn=1529-8817}}</ref> 


=== Coastal Eutrophication ===
=== Coastal Eutrophication ===
Sediment cores indicate a link between increasing coastal nutrient levels and an increase in ''Pseudo-nitzschia'' blooms.<ref name=":1" /> ''Pseudo-nitzschia'' also appears 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 6-25x as a result of stress.<ref name=":0" /> This increase allows them to enhance Fe acquisition needed for metabolic activities and can have devastating effects.
Sediment cores indicate a link between increasing coastal nutrient levels and an increase in ''Pseudo-nitzschia'' blooms.<ref name=":1" />

== Domioc Acid ==
Shellfish become contaminated after feeding on these toxic Pseudo-nitzschia blooms and can act as a vector to transfer domoic acid to humans upon ingested. 

DA acts as a potent glutamate agonist and responsible for Amnesiac Shellfish Poisoning (ASP) in humans. Effects can be as minor as vomiting, cramps and a headache, or as severe as permanent short-term memory loss, coma and death.<ref name=":8" /> For this reason, monitoring systems and management practices for recreational and commercail fishing are important in order to safeguard the health of marine animals, birds and humans.

Photosynthesis is essential for the production of this toxin. Periods of darkness or chemical inhibition of photosynthesis result in cessation of toxin production. Additionally, DA production peaks in the stationary phase of the growth cycle when cell division is slowed or absent. Production is minimal or non-existent during the exponential phase, and ceases completely during the death phase of the growth cycle.<ref name=":9" />

Many factors have been linked to promotion of DA production including sufficient light, elevated or decreased pH, nutrition limitations. A number of studies have raised evidence of numerous other factors.

In a specific species of this diatom, ''Pseudo-nitzschia cuspidata'', a link has been indicated between toxicity and photosynthesis photon flux density (PPFD). At a low PPFD, the exponential growth rate of these diatoms approximately halved and the cells were significantly more toxic.<ref name=":9" />

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 as a function of varying inorganic and organic nitrogen sources. The results vary too greatly by species. However, more toxin is produced when the nitrogen source could not sustain a high biomass, suggesting growth limitation seems to induce toxicity.<ref>{{Cite journal|last=Martin-Jézéquel|first=Véronique|last2=Calu|first2=Guillaume|last3=Candela|first3=Leo|last4=Amzil|first4=Zouher|last5=Jauffrais|first5=Thierry|last6=Séchet|first6=Véronique|last7=Weigel|first7=Pierre|date=2015-11-26|title=Effects of Organic and Inorganic Nitrogen on the Growth and Production of Domoic Acid by Pseudo-nitzschia multiseries and P. australis (Bacillariophyceae) in Culture|url=http://www.mdpi.com/1660-3397/13/12/7055|journal=Marine Drugs|language=en|volume=13|issue=12|pages=7067–7086|doi=10.3390/md13127055|pmc=4699229|pmid=26703627}}</ref>

The presence of zooplankton has also been shown to affect the toxicity of ''Pseudo-nitzschia'' blooms. The presence of these copepods was shown to enhance toxin production of ''Pseudo-nitzschia seriata''. This effect could be induced without physical contact indicating that the effect is chemically mediated.<ref>{{Cite journal|last=Tammilehto|first=Anna|last2=Nielsen|first2=Torkel Gissel|last3=Krock|first3=Bernd|last4=Møller|first4=Eva Friis|last5=Lundholm|first5=Nina|date=2015-02-01|title=Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods|url=http://www.sciencedirect.com/science/article/pii/S0166445X14003622|journal=Aquatic Toxicology|volume=159|pages=52–61|doi=10.1016/j.aquatox.2014.11.026}}</ref>

''Pseudo-nitzschia'' also appears 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 6-25x as a result of stress.<ref name=":0" /> This increase allows them to enhance Fe acquisition needed for metabolic activities and can have devastating effects.


== Further reading ==
== Further reading ==

Revision as of 21:59, 5 May 2016

Pseudo-nitzschia
Pseudo-nitzschia seriata
Scientific classification
Kingdom:
Chromalveolata
Phylum:
Heterokontophyta
Class:
Bacillariophyceae
Order:
Bacillariales
Family:
Bacillariaceae
Genus:
Pseudo-nitzschia

H. Perag. in H. Perag. and Perag.

Pseudo-nitzschia is a marine planktonic diatom genus containing some species capable of producing the neurotoxin domoic acid (DA), which is responsible for the neurological disorder known as amnesic shellfish poisoning (ASP). Currently, there are 46 known species, 19 of which are known to produced DA (see Known Species). It was originally hypothesized that only dinoflagellates could produce harmful algal toxins, but a deadly bloom of Pseudo-nitzschia occurred in 1987 in the bays of Prince Edward Island, Canada, and lead to an outbreak of ASP.[1] Over 100 people were effected by this outbreak after consuming contaminated mussels, three people died.[2] Blooms have since been characterized in coastal waters worldwide and have been linked to increasing marine nutrient concentrations.[3]

Morphology and Physiology

Pseudo-nitzschia are bilaterally symmetrical pennate diatoms. Cell walls are made up of elongated silica frustules. This dense silica wall leads to negative buoyancy, which can provide a number of advantages. This wall allows the diatoms to sink in order to avoid light inhibition or nutrient limitations as well as to protect against grazing zooplankton. These silica frustules also  contribute vastly to the sediment layers of the earth as well as to the fossil record. The contribution of diatoms to the fossil record makes them particularly useful in increasing understanding of various processes such as evaluating the degree of climate change. [4] It has been found that every atom of silicon that enters the ocean is incorporated into a diatom cell wall approximately 40 times before finally sinking to the sea floor.

Silica frustules contain a central raphe, which secretes mucilage that allows the cells to move by gliding.[5] Cells are often found in overlapped, stepped colonies and exhibit collective motility.[5] Pseudo-nitzschia are autotrophic organisms meaning they synthesize their own food through the use of light and nutrients in photosynthesis.These diatoms has a central vacuole to store nutrients for later use and a light harvesting system to protect itself against high intensity light.[4]

Taxonomy

Diatom lineage may go back 180 to 250 Myr. About 65 Myr ago, diatoms survived the mass extinction that saw the loss of about 85% of all species.[4] Up 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.[6] While the genus can be readily recognized using LM, identification of distinct species can require taxonomic expertise and be extremely time consuming. Species identification of this genus 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.[7]

This is a challenging concern because of the direct impacts on pubic health. It is common for toxogenic and non-toxogenic species to co-occur. Therefore, it is crucial to be able to discriminate between various Pseudo-nitzschia species in order to evaluate a potentially toxic 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 new DNA-microarray was developed for simultaneous detection of multiple Harmful Algal Bloom species with an emphasis on Pseudo-nitzschia. The total assay is is believed to have the potential to identify hundreds of species and differentiate between a large number 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. [8]

The nomenclatural history is given in Hasle (1995)[9] and Bates (2000).[10]

Life Cycle

Ornithine-urea Cycle

Physiological distribution and repackaging hub for inorganic carbon and nitrogen and contributes to the metabolic response of diatoms to episodic nitrogen availability. This cycle enables them to respond quickly and recover from prolonged periods of nutrient deprivation so they can rapidly proliferate. [4]

Resting Stages

Diatoms have the ability to enter two distinct resting stages in order to overcome periods of stress. A resting spore has a great capacity to survive over extended periods of nutrient deprivation. These morphologically distinct resting spores can settle to the bottom, where the nutrient concentration is higher, in order to avoid low nutrient concentrations during stratification. A resting cell is better able to rapidly respond when nutrients become available again. The is more often observed in freshwater and pennate diatoms like Pseudo-nitzschia.[4] 

Reproduction

Among diatoms, reproduction 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. In order 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 is an important phase in the life cycle of diatoms, and the basic mode of the sexual phase of reproduction appears to be conserved among Pseudo-nitzschia species.[11] Sexual reproduction leads to both production of genotypic diversity and formation of large sized initial cells through formation of  the auxospore. The sexual phase can be induced only in cells below a species-specific size threshold, however this is not the sole requirement. Many external cues also regulate the process in many diatoms, such as day length, irradiance and temperature. [12]

Upon mixing two strains of compatible mating type and of appropriate cell size for sexualization, some cells will align side by side and differentiate into gametangia. Two gametes are then produced within each gametangium, one active (+) and one passive (-). The active gamete migrates toward the passive partner and conjugates. The zygote is then transformed into an auxospore, which has no rigid frustule. Within the auxospore, a large initial cell is produced.[11]

Sexual reproduction appears to be restricted to the exponential growth phase and linked to cell density. A threshold cell concentration is required for commencement of sexualization. This concentration appears to vary by strain. Overall, reducing the distance and facilitating contact and/or perception of chemical cues between cells triggers the sexual phase, suggesting that cell accumulation is favorable for sexual reproduction. Additionally, the onset of the sexual phase 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.[12]

Genome

Very few species of Pseudo-nitzschia have had their genomes fully sequenced.

Pseudo-nitzschia multiseries has a genome consisting of 300 megabases (Mb).[13] 

Transcriptome

The sequencing of diatom genomes showed that this relatively recent eukaryotic lineage harbors a combination of genes and metabolic pathways first thought to be exclusive to plants and animals. Diatoms have the urea cycle and the ability to generate chemical energy from the breakdown of lipids that were considered distinctive animal features. Additionally, have the C4 photosynthetic pathway that was recorded only in some plants.[14]

Transcriptome sequences of of species of Pseudo-notzschia range from 34 million to 118 million.[14]

Habitat

Harmful algal blooms of Pseudo-nitzschia can be found in coastal regions worldwide. 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.[15] Recently, this genus of diatom has been detected in the open ocean as well as gulfs and bays, showing a presence in many diverse environemnts, including off the coasts of Canada, Portugal, France, Italy, Coratia, Greece, Ireland and Australia.[16] In general, diatoms thrive in relatively turbulent, nutrient-rich waters.[4] 

Harmful Bloom Dynamics

Harmful algal blooms (HABs) like Pseudo-nitzschia can be responsible for diseases and death of many marine creatures, as well as the humans that consume them. These negative impacts can occur through four main mechanisms: (i) oxygen depletion resulting from high biomass production; (ii) toxins, like DA, which can be transferred to humans; (iii) physical damage to skin and mucous membranes due to gill irritation or clogging due to sharp and needle-shaped diatoms; and (iv) gas bubble traumas caused by oxygen supersaturation form the high levels of photosynthetic activity.[17]

Unlike certain dinoflagellate blooms, domoic-acid-producing Pseudo-nitzschia species must be present in high concentrations (greater than 100,000 cells L−1) in order to contaminate shellfish at a level that would cease harvesting.[18]

The largest pseudo-nitzschia bloom on record occurred in September of 2004 off the coast of Washington state and British Columbia. The domoic acid levels reached 1.3 pg DA / cell and the maximum cell densities reached 13 x 10^6 cells / L.[19] 

Coastal Eutrophication

Sediment cores indicate a link between increasing coastal nutrient levels and an increase in Pseudo-nitzschia blooms.[3]

Domioc Acid

Shellfish become contaminated after feeding on these toxic Pseudo-nitzschia blooms and can act as a vector to transfer domoic acid to humans upon ingested. 

DA acts as a potent glutamate agonist and responsible for Amnesiac Shellfish Poisoning (ASP) in humans. Effects can be as minor as vomiting, cramps and a headache, or as severe as permanent short-term memory loss, coma and death.[16] For this reason, monitoring systems and management practices for recreational and commercail fishing are important in order to safeguard the health of marine animals, birds and humans.

Photosynthesis is essential for the production of this toxin. Periods of darkness or chemical inhibition of photosynthesis result in cessation of toxin production. Additionally, DA production peaks in the stationary phase of the growth cycle when cell division is slowed or absent. Production is minimal or non-existent during the exponential phase, and ceases completely during the death phase of the growth cycle.[19]

Many factors have been linked to promotion of DA production including sufficient light, elevated or decreased pH, nutrition limitations. A number of studies have raised evidence of numerous other factors.

In a specific species of this diatom, Pseudo-nitzschia cuspidata, a link has been indicated between toxicity and photosynthesis photon flux density (PPFD). At a low PPFD, the exponential growth rate of these diatoms approximately halved and the cells were significantly more toxic.[19]

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 as a function of varying inorganic and organic nitrogen sources. The results vary too greatly by species. However, more toxin is produced when the nitrogen source could not sustain a high biomass, suggesting growth limitation seems to induce toxicity.[20]

The presence of zooplankton has also been shown to affect the toxicity of Pseudo-nitzschia blooms. The presence of these copepods was shown to enhance toxin production of Pseudo-nitzschia seriata. This effect could be induced without physical contact indicating that the effect is chemically mediated.[21]

Pseudo-nitzschia also appears 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 6-25x as a result of stress.[1] This increase allows them to enhance Fe acquisition needed for metabolic activities and can have devastating effects.

Further reading

The general biology, physiology, toxicity and distribution of Pseudo-nitzschia species is reviewed in Bates and Trainer (2006),[22] Trainer et al. (2008),[23] Lelong et al. (2012) [24] and Trainer et al. (2012).[25]

Known Species

Known species of Pseudo-nitzschia (46):

Light and electron microscope images of Pseudo-nitzschia species are shown at the Nordic Microalgae website and scanning electron microscopy images at the Digital Microscopy Facility website.

Pseudo-nitzschia species that have been shown to produce domoic acid (19), although not all strains are toxigenic:

References

  1. ^ a b Maldonado, Maria T. (2002). "The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschia multiseries and Pseudo-nitzschia australis". Limnology and Oceanography. 47: 515–526. doi:10.4319/lo.2002.47.2.0515.
  2. ^ Lim, Hong-Chang; Leaw, Chui-Pin; Su, Suriyanti Nyun-Pau; Teng, Sing-Tung; Usup, Gires; Mohammad-Noor, Normawaty; Lundholm, Nina; Kotaki, Yuichi; Lim, Po-Teen (2012-10-01). "Morphology and Molecular Characterization of Pseudo-Nitzschia (bacillariophyceae) from Malaysian Borneo, Including the New Species Pseudo-Nitzschia Circumpora Sp. Nov". Journal of Phycology. 48 (5): 1232–1247. doi:10.1111/j.1529-8817.2012.01213.x. ISSN 1529-8817.
  3. ^ a b Parsons, Michael L.; Dortch, Quay (2002-03-01). "Sedimentological evidence of an increase in Pseudo-nitzschia (Bacillariophyceae)abundance in response to coastal eutrophication". Limnology and Oceanography. 47 (2): 551–558. doi:10.4319/lo.2002.47.2.0551. ISSN 1939-5590.
  4. ^ a b c d e f Kuwata, Akira; Jewson, David H. (2015-01-01). Ohtsuka, Susumu; Suzaki, Toshinobu; Horiguchi, Takeo; Suzuki, Noritoshi; Not, Fabrice (eds.). Ecology and Evolution of Marine Diatoms and Parmales. Springer Japan. pp. 251–275. doi:10.1007/978-4-431-55130-0_10#page-1. ISBN 9784431551294.
  5. ^ a b Lundholm, Nina; Moestrup, Øjvind. "The marine diatom Pseudo-nitzschia galaxiae sp. nov. (Bacillariophyceae): morphology and phylogenetic relationships". Phycologia. 41 (6): 594–605. doi:10.2216/i0031-8884-41-6-594.1.
  6. ^ Hasle, G.R. 1994. Pseudo-nitzschia as a genus distinct from Nitzschia (Bacillariophyceae). J. Phycol. 30: 1036-1039. [1]
  7. ^ Lim, H.-C., Leaw, C.-P., Su, S. N.-P., Teng, S.-T., Usup, G., Mohammad-Noor, N., Lundholm, N., Kotaki, Y. and Lim, P.-T. (2012), MORPHOLOGY AND MOLECULAR CHARACTERIZATION OFPSEUDO-NITZSCHIA (BACILLARIOPHYCEAE) FROM MALAYSIAN BORNEO, INCLUDING THE NEW SPECIES PSEUDO-NITZSCHIA CIRCUMPORA SP. NOV. Journal of Phycology, 48: 1232–1247. doi: 10.1111/j.1529-8817.2012.01213.x
  8. ^ Noyer, Charlotte; Abot, Anne; Trouilh, Lidwine; Leberre, Véronique Anton; Dreanno, Catherine (2015-05-01). "Phytochip: Development of a DNA-microarray for rapid and accurate identification of Pseudo-nitzschia spp and other harmful algal species". Journal of Microbiological Methods. 112: 55–66. doi:10.1016/j.mimet.2015.03.002.
  9. ^ Hasle, G.R. 1995. Pseudo-nitzschia pungens and P. multiseries (Bacillariophyceae): nomenclatural history, morphology, and distribution. J. Phycol. 31: 428-435. [2]
  10. ^ Bates, S.S. 2000. Domoic-acid-producing diatoms: another genus added! J. Phycol. 36: 978-983. [3]
  11. ^ a b Scalco, Eleonora; Amato, Alberto; Ferrante, Maria Immacolata; Montresor, Marina (2015-10-22). "The sexual phase of the diatom Pseudo-nitzschia multistriata: cytological and time-lapse cinematography characterization". Protoplasma: 1–11. doi:10.1007/s00709-015-0891-5. ISSN 0033-183X.
  12. ^ a b Scalco, Eleonora; Stec, Krzysztof; Iudicone, Daniele; Ferrante, Maria Immacolata; Montresor, Marina (2014-10-01). "The dynamics of sexual phase in the marine diatom Pseudo-nitzschia multistriata (Bacillariophyceae)". Journal of Phycology. 50 (5): 817–828. doi:10.1111/jpy.12225. ISSN 1529-8817.
  13. ^ Armbrust, E. Virginia (2009-05-14). "The life of diatoms in the world's oceans". Nature. 459 (7244): 185–192. doi:10.1038/nature08057. ISSN 0028-0836.
  14. ^ a b Dato, Valeria Di, Francesco Musacchia, Giuseppe Petrosino, Shrikant Patil, Marina Montresor, Remo Sanges, and Maria Immacolata Ferrante. "Transcriptome Sequencing of Three Pseudo-nitzschia Species Reveals Comparable Gene Sets and the Presence of Nitric Oxide Synthase Genes in Diatoms." Sci. Rep. Scientific Reports 5 (2015): 12329. Web.
  15. ^ "NOAA Coastal Science" (PDF).
  16. ^ a b Dhar, Bidhan Chandra; Cimarelli, Lucia; Singh, Kumar Saurabh; Brandi, Letizia; Brandi, Anna; Puccinelli, Camilla; Marcheggiani, Stefania; Spurio, Roberto (2015-05-06). "Molecular Detection of a Potentially Toxic Diatom Species". International Journal of Environmental Research and Public Health. 12 (5): 4921–4941. doi:10.3390/ijerph120504921. PMC 4454946. PMID 25955528.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  17. ^ Delegrange, A.; Vincent, D.; Courcot, L.; Amara, R. (2015-02-01). "Testing the vulnerability of juvenile sea bass (Dicentrarchus labrax) exposed to the harmful algal bloom (HAB) species Pseudo-nitzschia delicatissima". Aquaculture. 437: 167–174. doi:10.1016/j.aquaculture.2014.11.023.
  18. ^ Bates, Stephen (1998). "Bloom dynamics and physiology of domoic-acid-producing Pseudo-nitzschia species". Physiological Ecology of Harmfull Algal Blooms.
  19. ^ a b c Auro, Maureen E.; Cochlan, William P. (2013-02-01). "Nitrogen Utilization and Toxin Production by Two Diatoms of the Pseudo-nitzschia pseudodelicatissima Complex: P. cuspidata and P. fryxelliana". Journal of Phycology. 49 (1): 156–169. doi:10.1111/jpy.12033. ISSN 1529-8817.
  20. ^ Martin-Jézéquel, Véronique; Calu, Guillaume; Candela, Leo; Amzil, Zouher; Jauffrais, Thierry; Séchet, Véronique; Weigel, Pierre (2015-11-26). "Effects of Organic and Inorganic Nitrogen on the Growth and Production of Domoic Acid by Pseudo-nitzschia multiseries and P. australis (Bacillariophyceae) in Culture". Marine Drugs. 13 (12): 7067–7086. doi:10.3390/md13127055. PMC 4699229. PMID 26703627.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  21. ^ Tammilehto, Anna; Nielsen, Torkel Gissel; Krock, Bernd; Møller, Eva Friis; Lundholm, Nina (2015-02-01). "Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods". Aquatic Toxicology. 159: 52–61. doi:10.1016/j.aquatox.2014.11.026.
  22. ^ Bates, S.S. and V.L. Trainer. 2006. The ecology of harmful diatoms. In: E. Granéli and J. Turner [eds.] Ecology of harmful algae. Ecological Studies, Vol. 189. Springer-Verlag, Heidelberg, p. 81-93. PDF; 181 KB
  23. ^ Trainer, V.L., B.M. Hickey, and S.S. Bates. 2008. Toxic diatoms. In: P.J. Walsh, S.L. Smith, L.E. Fleming, H. Solo-Gabriele, and W.H. Gerwick [eds.], Oceans and human health: risks and remedies from the sea. Elsevier Science Publishers, New York, p. 219-237. PDF 2.7 MB
  24. ^ Lelong, A., H. Hégaret, P. Soudant, and S.S. Bates. 2012. Pseudo-nitzschia (Bacillariophyceae) species, domoic acid and amnesic shellfish poisoning: revisiting previous paradigms. Phycologia 51: 168-216. PDF; 1.8 MB
  25. ^ Trainer, V.L., S.S. Bates, N. Lundholm, A.E. Thessen, W.P. Cochlan, N.G. Adams, and C.G. Trick. 2012. Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health. Harmful Algae 14: 271–300. Publisher's abstract and link to PDF file

External links

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