Editing Cyanotoxin (section)

==Cyclic peptides==
A [[peptide]] is a short [[polymer]] of [[amino acid]]s linked by [[peptide bond]]s. They have the same chemical structure as [[protein]]s, except they are shorter. In a [[cyclic peptide]], the ends link to form a stable circular chain. In mammals this stability makes them resistant to the process of digestion and they can [[bioaccumulate]] in the liver. Of all the cyanotoxins, the cyclic peptides are of most concern to human health. The microcystins and nodularins poison the liver, and exposure to high doses can cause death. Exposure to low doses in drinking water over a long period of time may promote liver and other tumours.<ref name="Chorus&Bartram" />

===Microcystins===
[[File:Microcystin-LR.svg|thumb|[[Microcystin LR]]]]

As with other cyanotoxins, [[microcystin]]s were named after the first organism discovered to produce them, ''Microcystis aeruginosa''. However it was later found other cyanobacterial genera also produced them.<ref name="Chorus&Bartram" /> There are about 60 known variants of microcystin, and several of these can be produced during a bloom. The most reported variant is [[microcystin-LR]], possibly because the earliest commercially available chemical standard analysis was for microcystin-''LR''.<ref name="Chorus&Bartram">{{Cite book |last1=Chorus |first1=Ingrid |url=https://www.taylorfrancis.com/books/9781003081449 |title=Toxic Cyanobacteria in Water: A Guide to Their Public Health Consequences, Monitoring and Management |last2=Welker |first2=Martin |date=2021-03-07 |publisher=CRC Press |isbn=978-1-003-08144-9 |edition=2 |location=London |language=en |doi=10.1201/9781003081449}}</ref>

Blooms containing microcystin are a problem worldwide in freshwater ecosystems.<ref name="PelaezAntoniou2010">{{Cite book|last1=Pelaez|first1=Miguel|title=Xenobiotics in the Urban Water Cycle|last2=Antoniou|first2=Maria G.|last3=He|first3=Xuexiang|last4=Dionysiou|first4=Dionysios D.|last5=de la Cruz|first5=Armah A.|last6=Tsimeli|first6=Katerina|last7=Triantis|first7=Theodoros|last8=Hiskia|first8=Anastasia|last9=Kaloudis|first9=Triantafyllos|last10=Williams|first10=Christopher|last11=Aubel|first11=Mark|last12=Chapman|first12=Andrew|last13=Foss|first13=Amanda|last14=Khan|first14=Urooj|last15=O’Shea|first15=Kevin E.|last16=Westrick|first16=Judy|chapter=Sources and Occurrence of Cyanotoxins Worldwide |display-authors=6|volume=16|year=2010|pages=101–127|issn=1566-0745|doi=10.1007/978-90-481-3509-7_6|series=Environmental Pollution|isbn=978-90-481-3508-0}}</ref> Microcystins are cyclic peptides and can be very toxic for plants and animals including humans. They bioaccumulate in the [[liver]] of fish, in the [[hepatopancreas]] of mussels, and in zooplankton. They are [[hepatotoxic]] and can cause serious damage to the liver in humans.<ref name="Chorus&Bartram" /> In this way they are similar to the nodularins (below), and together the microcystins and nodularins account for most of the toxic cyanobacterial blooms in fresh and brackish waters.<ref name="Sivonen&Jones" /> In 2010, a number of [[sea otter]]s were poisoned by microcystin. Marine [[bivalve]]s were the likely source of hepatotoxic [[shellfish poisoning]]. This was the first confirmed example of a marine mammal dying from ingesting a cyanotoxin.<ref name=Milleretal>{{cite journal  |vauthors=Miller MA, Kudela RM, Mekebri A, Crane D, Oates SC, etal | year = 2010 | title = Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters | journal = PLOS ONE | volume = 5 | issue = 9| page = e12576 | doi = 10.1371/journal.pone.0012576 | editor1-last = Thompson | editor1-first = Ross | pmid=20844747 | pmc=2936937|bibcode = 2010PLoSO...512576M | doi-access = free }}</ref>

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===Nodularins===
[[File:Nodularin R.svg|thumb|[[Nodularin-R]]]]

The first nodularin variant to be identified was [[nodularin-R]], produced by the cyanobacterium ''[[Nodularia|Nodularia spumigena]]''.<ref>{{cite journal |vauthors=Sivonen K, Kononen K, Carmichael WW, Dahlem AM, Rinehart KL, Kiviranta J, Niemela SI |title=Occurrence of the hepatotoxic cyanobacterium Nodularia spumigena in the Baltic Sea and structure of the toxin |journal=Appl. Environ. Microbiol. |volume=55 |issue=8 |pages=1990–5 |year=1989 |doi=10.1128/aem.55.8.1990-1995.1989 |pmid=2506812 |pmc=202992|bibcode=1989ApEnM..55.1990S }}</ref> This cyanobacterium blooms in water bodies throughout the world. In the [[Baltic Sea]], marine blooms of ''Nodularia spumigena'' are among some of the largest cyanobacterial mass events in the world.<ref>{{cite journal |author1=David P. Fewer DP |author2=Köykkä K |author3=Halinen K |author4=Jokela J |author5=Lyra C |author6=Sivonen K | year = 2009 | title = Culture-independent evidence for the persistent presence and genetic diversity of microcystin-producing Anabaena (Cyanobacteria) in the Gulf of Finland | journal = Environmental Microbiology | volume = 11 | issue = 4| pages = 855–866 | doi = 10.1111/j.1462-2920.2008.01806.x | pmid = 19128321 }}</ref> (Parts of nine industrialized countries drain into the Baltic Sea, which has little water exchange with the North Sea and Atlantic Ocean. It is consequently one of the more polluted bodies of water in the world (nutrient-rich, from the perspective of cyanobacteria).)

Globally, the most common toxins present in cyanobacterial blooms in fresh and brackish waters are the cyclic peptide toxins of the nodularin family. Like the microcystin family (above), nodularins are potent hepatotoxins and can cause serious damage to the liver. They present health risks for wild and domestic animals as well as humans, and in many areas pose major challenges for the provision of safe drinking water.<ref name="Sivonen&Jones" />

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