Pseudo-nitzschia

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). 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] Blooms have since been characterized in coastal waters worldwide and have been linked to increasing marine nutrient concentrations.[2]

Morphology and Physiology

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.[3] Cells are often found in overlapped, stepped colonies and exhibit collective motility.[3] Species reproduction is often asexual and results in the size reduction of cells. They then undergo sexual reproduction to revert to their original size.[4] Pseudo-nitzschia are autotrophic organisms meaning they synthesize their own food through the use of light and nutrients in photosynthesis.

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.[5] The nomenclatural history is given in Hasle (1995)[6] and Bates (2000).[7]

Harmful Bloom Dynamics

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.[8] Unlike certain dinoflagellate blooms, DA 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.[4] Shellfish become contaminated after feeding on these toxic Pseudo-nitzschia blooms and they can act as a vector that transfers the DA to humans if ingested.[9] This often leads to ASP in humans, which can have debilitating effects such as permanent short-term memory loss.[1]

Coastal Eutrophication

Sediment cores indicate a link between increasing coastal nutrient levels and an increase in Pseudo-nitzschia blooms.[2] 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),[10] Trainer et al. (2008),[11] Lelong et al. (2012) [12] and Trainer et al. (2012).[13]

Known Species

Known species of Pseudo-nitzschia (46):

Light and electron microscope images of Pseudo-nitzschia species are shown at the Nordic Microalgae website.

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

References

  1. 1 2 3 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. 1 2 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.
  3. 1 2 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.
  4. 1 2 Bates, Stephen (1998). "Bloom dynamics and physiology of domoic-acid-producing Pseudo-nitzschia species". Physiological Ecology of Harmfull Algal Blooms.
  5. ↑ Hasle, G.R. 1994. Pseudo-nitzschia as a genus distinct from Nitzschia (Bacillariophyceae). J. Phycol. 30: 1036-1039.
  6. ↑ Hasle, G.R. 1995. Pseudo-nitzschia pungens and P. multiseries (Bacillariophyceae): nomenclatural history, morphology, and distribution. J. Phycol. 31: 428-435.
  7. ↑ Bates, S.S. 2000. Domoic-acid-producing diatoms: another genus added! J. Phycol. 36: 978-983.
  8. ↑ "NOAA Coastal Science" (PDF).
  9. ↑ "Pseudo-nitzschia toxins". www.mbari.org. Retrieved 2015-10-29.
  10. ↑ 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
  11. ↑ 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
  12. ↑ 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
  13. ↑ 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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