Henneguya zschokkei explained

Henneguya zschokkei or Henneguya salminicola is a species of a myxosporean endoparasite. It afflicts several salmon in the genera Oncorhynchus and Salmo,^{[1] [2]} where it causes milky flesh or tapioca disease.^[3] H. zschokkei is notable for its reliance on an exclusively anaerobic metabolism as well as its lack of mitochondria and mitochondrial DNA. It is the only known multicellular animal that does not require oxygen to survive.^[4]

Description

Henneguya zschokkei is found in fish as an ovoid spore with two anterior polar capsules and two long caudal appendages.^[5] Individuals are very small (about 10 micrometers in diameter),^[6] but are found aggregated into cysts 3–6 mm in diameter at any place in the animal's musculature.^[7]

Metabolism

So far as is known, H. zschokkei is unique among multicellular animals because it does not make use of the aerobic respiration of oxygen. The creature relies instead on an exclusively anaerobic metabolism, making it the only known member of the eukaryotic animal kingdom to shun oxygen as the foundation of its metabolism.^[8] It also lacks a mitochondrial genome and therefore mitochondria.^[9]

H. zschokkei is ultimately a highly derived cnidarian and is distantly related to jellyfish, sea anemone and corals. However, this obligate internal parasite so little resembles cnidarians (let alone other multicellular animals) that it, along with many other species in the class Myxosporea, were initially categorized as protozoa. It is nevertheless most closely related to jellyfish. This species, like most myxosporeans, lacks many of the diagnostic criteria that identify cnidarians. Indeed, it is without nervous, epithelial, gut or muscle cells of any kind.^[10]

This parasite has not only lost its mitochondria and the mitochondrial DNA residing in them, but also the nuclear genes that code for mitochondrial reproduction. What genetic instructions for these functions that remain lie in useless pseudogenes.^[11]

Origins

The origin and cause of H. zschokkei's highly reduced genome are not yet known. While eukaryotes are known for aerobic respiration, a few unicellular lineages native to hypoxic environments have also lost this capacity. In the absence of oxygen these single-celled organisms lose the portions of their genome that anticipate and govern aerobic respiration. These unusual eukaryotes have developed mitochondria-related organelles (MROs) that fulfill many of the functions of conventional mitochondria. However there is no evidence of such an adaptation in the multicellular H. zschokkei.

One hypothesis put forward to explain the highly unusual habit of H. zschokkei and its fellow myxosporeans invokes the cancers of cnidarians. On this explanation, animals such as H. zschokkei were originally cancerous growths in free-swimming jellyfish that escaped their parent organism, thereafter becoming a separate species that parasitized other animals. Such an origin is referred to as a SCANDAL, a loose acronym of the phrase speciated by cancer development in animals.^[12]

Hosts

Known hosts of Henneguya zschokkei include:^[13]

• Oncorhynchus gorbuscha (Pink salmon)
• Oncorhynchus keta (Chum salmon)
• Oncorhynchus kisutch (Coho salmon)
• Oncorhynchus nerka (Sockeye salmon)
• Anadromous forms of Oncorhynchus mykiss (Rainbow trout)
• Oncorhynchus tshawytscha (Chinook salmon)
• Salmo salar (Atlantic Salmon)

See also

Taxa

• Cryptosporidium parvum, a protist (Apicomplexa) without genes in its mitochondria
• Mastigamoeba, an anaerobic protist (Amoebozoa) without mitochondria
• Monocercomonoides, a protist (Metamonad) without mitochondria
• Loricifera, other metazoans; some species don't require oxygen and may also lack mitochondria

Structures

• hydrogenosome, an organelle of some anaerobic taxa

Further reading

• Lebbad . Marianne . Willcox . Michael . Spores of Henneguya salminicola in Human Stool Specimens . Journal of Clinical Microbiology . June 1998 . 36 . 6 . 1820 . 10.1128/JCM.36.6.1820-1820.1998 . 9620434 . 104934 .
• Fish . Frederic F. . Observations on Henneguya salminicola Ward, a Myxosporidian Parasitic in Pacific Salmon . The Journal of Parasitology . 1939 . 25 . 2 . 169–172 . 10.2307/3272359 . 3272359 .
• Clouthier . Sharon C . Gunning . Derek J . Olafson . Robert W . Kay . William W . Antigenic characterization of Henneguya salminicola . Molecular and Biochemical Parasitology . December 1997 . 90 . 2 . 543–548 . 10.1016/s0166-6851(97)00200-4 . 9476801 .
• Stojanovski . Stojmir . Spirkoski . Zoran . Hristovski . Miso . Hristovski . Nikola . Blazhekovikj - Dimovska . Dijana . First finding of parasitic lesions caused by Henneguya zschokkei (Myxosporidia: Myxobolidae) in frozen market salmon in Macedonia . Journal of Hygienic Engineering and Design . 2012 . 1 . 139–141 .

External links

• Web site: Knutsjuka hos laxfisk . Knuckle disease in salmonids . SVA . sv .
• GBIF: Henneguya salminicola Ward, 1919. Id:6881057, source: World Register of Marine Species
• GBIF: Henneguya zschokkei Ward, 1919. Id:6881028, source: Artsnavnebasen

Notes and References

1. Ward . Henry B. . Notes on North American Myxosporidia . The Journal of Parasitology . 1919 . 6 . 2 . 49–64 . 10.2307/3270895 . 3270895 . 88435361 . 2021-08-04 . 2021-08-17 . https://web.archive.org/web/20210817150635/https://digitalcommons.unl.edu/manterlibrary/22/ . live .
2. News: Greenwood . Veronique . This Parasite Doesn't Need Oxygen to Survive - But that's not the weirdest thing about this jellyfish cousin that turns up in the muscles of salmon. . 28 February 2020 . . 5 March 2020 . 30 April 2023 . https://web.archive.org/web/20230430105217/https://www.nytimes.com/2020/02/28/science/parasite-oxygen-mitochondria.html . live .
3. Web site: Henneguya salminicola . fishpathogens.net . Oregon State University . Oregon Department of Fish and Wildlife . 2020-02-28 . 2020-02-28 . https://web.archive.org/web/20200228110410/https://fishpathogens.net/pathogen/henneguya-salminicola . live .
4. Web site: First Known Non-oxygen Breathing Animal. .
5. Book: Meyers, T. R. . Burton, T. . Bentz, C. . Starkey, N. . Common diseases of wild and cultured fishes in Alaska. . July 2008 . Alaska Department of Fish and Game . Fish Pathology Laboratories . 2020-03-04 . 2019-07-19 . https://web.archive.org/web/20190719140230/http://www.north-slope.org/assets/images/uploads/ADFG_2014_fish_disease_book-1.pdf . dead .
6. Web site: Spores of H. salminicola from a human stool specimen . ResearchGate.
7. News: Brandon Specktor . 24 February 2020 . Scientists discover first known animal that doesn't breathe . Live Science . 5 April 2020 . 27 June 2023 . https://web.archive.org/web/20230627153921/https://www.livescience.com/first-non-breathing-animal.html . live .
8. Yahalomi . Dayana . Atkinson . Stephen D. . Neuhof . Moran . Chang . E. Sally . Philippe . Hervé . Cartwright . Paulyn . Bartholomew . Jerri L. . Huchon . Dorothée . 19 February 2020 . A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome . Proceedings of the National Academy of Sciences . 117 . 10 . 5358–5363 . 10.1073/pnas.1909907117 . 7071853 . 32094163 . free. 2020PNAS..117.5358Y .

   Lay summary: Web site: Unique non-oxygen breathing animal discovered: The tiny relative of the jellyfish is parasitic and dwells in salmon tissue . ScienceDaily . en . 2020-02-28 . 2020-02-26 . https://web.archive.org/web/20200226234654/https://www.sciencedaily.com/releases/2020/02/200225114408.htm . live .

9. Web site: This Is The First Animal Ever Found That Doesn't Need Oxygen to Survive . Nature . Michelle . Starr . 2024-06-21 . 2024-06-23 . en-US . Science Alert.
10. Panchin . A. Y. . Aleoshin . V. V. . Panchin . Y. V. . 2019-01-23 . From tumors to species: a SCANDAL hypothesis . Biology Direct . en . 14 . 1 . 3 . 10.1186/s13062-019-0233-1 . 1745-6150 . 6343361 . 30674330 . free .
11. Yahalomi . Dayana . Atkinson . Stephen . Neuhof . Moran . Chang . E. Sally . Phillipe . Hervé . Cartwright . Paulyn . Bartholomew . Jerri . Hutchon . Dorothée . 2020 . A cnidarian parasite of salmon (Myxozoa: Henneguya) lacks a mitochondrial genome . Proceedings of the National Academy of Sciences . 117 . 10 . 5358–5363 . 10.1073/pnas.1909907117 . 7071853 . 32094163 . free. 2020PNAS..117.5358Y .
12. Panchin . A. Y. . Aleoshin . V. V. . Panchin . Y. V. . 2019-01-23 . From tumors to species: a SCANDAL hypothesis . Biology Direct . en . 14 . 1 . 3 . 10.1186/s13062-019-0233-1 . 1745-6150 . 6343361 . 30674330 . free .
13. Buchtová . H. . Dyková . I. . Vršková . D. . Krkoška . L. . Záchyt lososa masivně infikovaného myxosporidií Henneguya zschokkei . Myxosporidia Henneguya zschokkei massive infection in a salmon . cs . Veterinářství . 2004 . 54 . 47–48 . 2021-08-04 . 2021-08-04 . https://web.archive.org/web/20210804235645/https://www.vetweb.cz/zachyt-lososa-masivne-infikovaneho-myxosporidii-henneguya-zschokke/ . live .