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Chaosis agenusofsingle-celledamoeboidorganismsin the familyAmoebidae.The largest and most-known species, the so-called "giant amoeba" (Chaos carolinensis), can reach lengths up to 5 mm, although most specimens fall between 1 and 3 mm.[3][4][5]
| Chaos | |
|---|---|
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| Chaos carolinensis | |
Scientific classification
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| Domain: | Eukaryota |
| Phylum: | Amoebozoa |
| Class: | Tubulinea |
| Order: | Euamoebida |
| Family: | Amoebidae |
| Genus: | Chaos Linnaeus,1767[1] |
| Type species | |
| Chaos proteus (Pallas 1766) Linnaeus 1767
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| Species | |
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| Synonyms[2] | |
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Members of this genus closely resemble those of the genusAmoebaand share the same general morphology, producing numerous cylindricalpseudopods,each of which is rounded at the tip.[6]However, whileAmoebahave a singlenucleus,Chaoscan have as many as a thousand. Because of this attribute,C. carolinensiswas once placed in the genusPelomyxaalongside the giantmultinucleateamoebaPelomyxa palustris.Recently, molecular phylogenetic studies of this species have confirmed the view of some earlier researchers[7]that it is more closely related toAmoebathan toPelomyxa.[8]The species is now placed in the independent genusChaos,a sister group toAmoeba.
Dietary habits
editChaosspecies are versatileheterotrophs,able to feed on bacteria, algae, other protists, and even smallmulticellularinvertebrates.[4]Like allAmoebozoa,they take in food byphagocytosis,encircling food particles with its pseudopodia, then enclosing them within a food ball, orvacuole,where they are broken down by enzymes. The cell does not have a mouth orcytostome,nor is there any fixed site on the cell membrane at which phagocytosis normally occurs.[9]
Movement
editThe cell's membrane, orplasmalemma,is extremely flexible, allowing the organism to change shape from one moment to the next. Thecytoplasmwithin the membrane is conventionally described as having two parts: the internal fluid, orendoplasm,which contains loose granules and food vacuoles, as well as organelles such as nuclei andmitochondria;and a more viscousectoplasmaround the perimeter of the cell, which is relatively clear and contains no conspicuous granules. Like other lobose amoebae,Chaosmove by extendingpseudopodia.As a new pseudopod is extended, a variable zone of ectoplasm forms at the leading edge and a fountaining stream of endoplasm circulates within. The effort of describing these motions, and explaining how they result in the cell's forward movement, has generated a large body of scientific literature.[10]
Early history and naming controversy
edit
The genusChaoshas had a long and often confusing history. In 1755,Rösel von Rosenhofsaw and depicted an amoeboid he named "der kleine Proteus"(" the little Proteus ").[11]Three years later, Linnaeus gave Rösel's creature the nameVolvox chaos.However, because the nameVolvoxhad already been applied to a genus of flagellate algae, he later changed it toChaos chaos.In subsequent decades, as new names and species proliferated, accounts ofChaos,under a variety of synonyms, became so thoroughly entangled with descriptions of similar organisms, that it is virtually impossible to differentiate one historic amoeboid from another. In 1879, Joseph Leidy suggested collapsing all the "common" large, freshwater amoebae into one species, which he proposed to callAmoeba proteus.A dozen species, including several that had been identified as belonging toChaos,were to be regarded as synonyms ofAmoeba proteus.However, in the description he gives of this organism, it is clearly defined as auninucleateamoeba, unlike the modernChaos.[12]
In 1900, the biologistH. V. Wilson,at the University of North Carolina, discovered and isolated a giant amoeba that resembledAmoeba proteusbut had cellular nuclei numbering in the hundreds. Since there existed already a genus of giant multinucleate amoebae,Pelomyxa,Wilson placed his organism in that taxon, naming itPelomyxa carolinensis.[3]This amoeba was easily cultivated and became a widely distributed and studied laboratory organism.
In 1926, Asa A. Schaeffer argued thatPelomyxa carolinensiswas, in fact, identical to the amoeba that had been seen by Rösel in 1755, the "little Proteus" which Linnaeus had namedChaos chaos.Therefore, he urged that, in keeping with theprinciple of prioritygoverning biological nomenclature, the name of the organism should beChaos chaos.Several investigators argued vigorously against the validity of that name,[13][14]but others adopted it. A third faction accepted the validity of the genusChaosfor Wilson's amoeba, but retained the second half of the binomial, referring to the organism asChaos carolinensis.[15]By the early 1970s, all three names were in use concurrently, by various investigators. However, studies of the fine structure and physiology of the amoeba made it increasingly clear that there were profound differences between it and the otherPelomyxa(including the complete absence, in truePelomyxa,of mitochondria).[16]Since then, a nomenclatural consensus has emerged, and today the organism is generally known asChaos carolinensis,as first proposed by Robert L. King and Theodore L. Jahn in 1948.[15]
Recent phylogeny
editUntil quite recently, the genusChaoswas included, along with all other protists that extend lobose pseudopods or move about byprotoplasmicflow, in the phylumSarcodina.[17]Molecular phylogenies based on the examination ofribosomal DNA,have shown that Sarcodina is apolyphyleticgrouping: that some amoeboids shared a more recent common ancestor with members of other phyla than with other Sarcodina. Consequently, the amoeboids of Sarcodina have been distributed among two newly created supergroups,RhizariaandAmoebozoa.Chaosand its close relative,Amoeba,are now placed in the latter, within the order Tubulinida: naked amoebas (lacking atest,or shell), either monopodial or possessing somewhat cylindrical pseudopods, with non-adhesive uroid (a region at the posterior of the cell which has a crumpled appearance).[1]
While themonophylyof Amoebozoa has yet to be established, current information confirms the status ofChaosandAmoebaas closely related taxa within the group. However, the same research raises questions about the monophyly of the genusChaos,sinceChaos nobilemay bebasalto a group containingChaos carolinensisand at least two species ofAmoeba,[17]as illustrated below, following Pawlowski and Burki (2009):
References
edit- ^abAdl, Sina M.; et al. (October 2005)."The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists".Journal of Eukaryotic Microbiology.52(5): 399–451.doi:10.1111/j.1550-7408.2005.00053.x.PMID16248873.S2CID8060916.
- ^"Chaos".Global Biodiversity Information Facility.Retrieved2023-03-03.
- ^abWilson, H. V.(July 1900)."Notes on a Species of Pelomyxa".The American Naturalist.34(403): 535–550.doi:10.1086/277702.JSTOR2453844.
- ^abKudo, Richard (1954).Protozoology(4th ed.).Springfield, Illinois:Charles C. Thomas. p.442.
- ^Deng, Yuru; et al. (2002). "Fasting induces cyanide-resistant respiration and oxidative stress in the amoeba Chaos carolinensis: implications for the cubic structural transition in mitochondrial membranes".Protoplasma.219(3–4): 160–167.doi:10.1007/s007090200017.PMID12099216.S2CID21590883.
- ^Patterson, David (1996).Free-Living Freshwater Protozoa: A Colour Guide.London:Manson.p. 99.ISBN1-874545-40-5.
- ^Short, Robert B. (1946)."Observations on the Giant Amoeba, Amoeba Carolinensis (Wilson, 1900)".The Biological Bulletin.90(1): 8–18.doi:10.2307/1538058.JSTOR1538058.PMID21014274.
- ^Bolivar, Ignacio; et al. (2001)."SSU rRNA-based Phylogenetic Position of the Genera Amoeba and Chaos (Lobosea, Gymnamoebia): The Origin of Gymnamoebae Revisited".Molecular Biology and Evolution.18(12): 2306–2314.doi:10.1093/oxfordjournals.molbev.a003777.PMID11719580.
- ^Thorp, James H. (2001).Ecology and Classification of North American Freshwater invertebrates.San Diego: Academic. pp.71.ISBN0-12-690647-5.
- ^Allen, RD; Allen, RS (1978). "Cytoplasmic Streaming in Amoeboid Movement".Annual Review of Biophysics and Bioengineering.7:469–495.doi:10.1146/annurev.bb.07.060178.002345.PMID352246.
- ^Rösel von Rosenhof, A.J. 1755. Der monatlich-herausgege benen Insecten-Belustigung erster [bis vierter] Theil... J.J. Fleischmann: Nürnberg. Vol. 3, Tab. 101,[1],p. 621,[2],p. 622,[3].
- ^Leidy, Joseph (1879).Fresh-water Rhizopods of North America.Washington: Government Printing Office. pp.30–35.
- ^Wilber, CG (1947). "Concerning the Correct Name of the Rhizopod, Pelomyxa carolinensis".Transactions of the American Microscopical Society.66(1): 99–101.doi:10.2307/3223328.JSTOR3223328.PMID20242308.
- ^Kudo, Richard (1959). "Pelomyxa and Related Organisms".Annals of the New York Academy of Sciences.78(2): 474–486.Bibcode:1959NYASA..78..474K.doi:10.1111/j.1749-6632.1959.tb56118.x.S2CID84452764.
- ^abKing, Robert L.; Jahn, Theodore L. (19 March 1948). "Concerning the Genera of Amebas".Science.107(2777): 293–4.Bibcode:1948Sci...107..293K.doi:10.1126/science.107.2777.293.JSTOR1675718.PMID17791177.
- ^Chapman-Andresen, Cicely (1971). "Biology of the Large Amoebae".Annual Review of Microbiology.25:27–48.doi:10.1146/annurev.mi.25.100171.000331.PMID5005027.
- ^abPawlowski, J.; Burki, F. (Jan–Feb 2009)."Untangling the phylogeny of amoeboid protists".Journal of Eukaryotic Microbiology.56(1): 16–26.doi:10.1111/j.1550-7408.2008.00379.x.PMID19335771.S2CID5794367.