Henneguya zschokkei
Henneguya zschokkei in salmon
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Cnidaria
Class: Myxosporea
Order: Bivalvulida
Family: Myxobolidae
Genus: Henneguya
Species:
H. zschokkei
Binomial name
Henneguya zschokkei
(Gurley, 1894)
Synonyms[1]
  • Henneguya salminicola Ward, 1919

Henneguya zschokkei or Henneguya salminicola is a species of a myxosporean endoparasite. It afflicts several salmon in the genera Oncorhynchus and Salmo.[2][3] It causes milky flesh or tapioca disease.[1] H. zschokkei is notable for its lack of mitochondria, mitochondrial DNA, aerobic respiration and its reliance on an exclusively anaerobic metabolism.[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

H. zschokkei is a highly unusual among multicellular animals because it does not rely on the aerobic respiration of oxygen. The creature instead relies on an exclusively anaerobic metabolism.[8][7] It lacks a mitochondrial genome and therefore mitochondria, making it one of the only known members of the eukaryotic animal kingdom to shun oxygen as the foundation of its metabolism.

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 other multicellular animals (let alone cnidarians) that it, along with many other species in 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.[9]

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.[4]

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.[4]

One theory 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.[10]

Hosts

Known hosts of Henneguya zschokkei include:[11]

See also

Taxa
Structures

References

  1. 1 2 "Henneguya salminicola". fishpathogens.net. Oregon State University. Oregon Department of Fish and Wildlife. Retrieved 2020-02-28.
  2. ↑ Ward, Henry B. (1919). "Notes on North American Myxosporidia". The Journal of Parasitology. 6 (2): 49–64. doi:10.2307/3270895. JSTOR 3270895. S2CID 88435361.
  3. ↑ Greenwood, Veronique (28 February 2020). "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". The New York Times. Retrieved 5 March 2020.
  4. 1 2 3 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. doi:10.1073/pnas.1909907117. PMC 7071853. PMID 32094163.
  5. ↑ Meyers, T. R.; Burton, T.; Bentz, C.; Starkey, N. (July 2008). Common diseases of wild and cultured fishes in Alaska (PDF). Alaska Department of Fish and Game. Yukon River Drainage Fisheries Association. {{cite book}}: |work= ignored (help)
  6. ↑ "Spores of H. salminicola from a human stool specimen" – via ResearchGate.
  7. 1 2 Brandon Specktor (24 February 2020). "Scientists discover first known animal that doesn't breathe". Live Science.
  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. doi:10.1073/pnas.1909907117. PMC 7071853. PMID 32094163.; Lay summary: "Unique non-oxygen breathing animal discovered: The tiny relative of the jellyfish is parasitic and dwells in salmon tissue". ScienceDaily.
  9. ↑ Panchin, A. Y.; Aleoshin, V. V.; Panchin, Y. V. (2019-01-23). "From tumors to species: a SCANDAL hypothesis". Biology Direct. 14 (1): 3. doi:10.1186/s13062-019-0233-1. ISSN 1745-6150. PMC 6343361. PMID 30674330.
  10. ↑ Panchin, A. Y.; Aleoshin, V. V.; Panchin, Y. V. (2019-01-23). "From tumors to species: a SCANDAL hypothesis". Biology Direct. 14 (1): 3. doi:10.1186/s13062-019-0233-1. ISSN 1745-6150. PMC 6343361. PMID 30674330.
  11. ↑ Buchtová, H.; Dyková, I.; Vršková, D.; Krkoška, L. (2004). "Záchyt lososa masivně infikovaného myxosporidií Henneguya zschokkei" [Myxosporidia Henneguya zschokkei massive infection in a salmon]. Veterinářství (in Czech). 54: 47–48.

Further reading

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