Editing Entamoeba

{{Short description|Genus of internal parasites}}
{{Distinguish|Endamoeba}}
{{Automatic taxobox
| image = Entamoeba histolytica.jpg
| image_caption = ''[[Entamoeba histolytica]]'' [[trophozoite]]
| taxon = Entamoeba
| authority = Casagrandi & Barbagallo, 1897
| type_species = ''Entamoeba coli''
| type_species_authority = (Grassé 1879) Casagrandi & Barbagallo 1895
| subdivision_ranks = Species
| subdivision =
''[[Entamoeba bangladeshi|E. bangladeshi]]''<br/>
''[[Entamoeba bovis|E. bovis]]''<br/>
''[[Entamoeba chattoni|E. chattoni]]''<br/>
''[[Entamoeba coli|E. coli]]''<br/>
''[[Entamoeba dispar|E. dispar]]''<br/>
''[[Entamoeba ecuadoriensis|E. ecuadoriensis]]''<br/>
''[[Entamoeba equi|E. equi]]''<br/>
''[[Entamoeba gingivalis|E. gingivalis]]''<br/>
''[[Entamoeba hartmanni|E. hartmanni]]''<br/>
''[[Entamoeba histolytica|E. histolytica]]''<br/>
''[[Entamoeba insolita|E. insolita]]''<br/>
''[[Entamoeba invadens|E. invadens]]''<br/>
''[[Entamoeba moshkovskii|E. moshkovskii]]''<br/>
''[[Entamoeba muris|E. muris]]''<br/>
''[[Entamoeba nuttalli|E. nuttalli]]''<br/>
''[[Entamoeba polecki|E. polecki]]''<br/>
''[[Entamoeba ranarum|E. ranarum]]''<br/>
''[[Entamoeba struthionis|E. struthionis]]''<br/>
''[[Entamoeba suis|E. suis]]''<br/>
''[[Entamoeba terrapinae|E. terrapinae]]''
| synonyms = 
* [[Councilmania]] <small>[[Charles Atwood Kofoid|Kofoid]] & [[Olive Swezy|Swezy]] 1921</small>
}}

'''''Entamoeba''''' is a [[genus]] of [[Amoebozoa]] found as internal [[parasitism|parasite]]s or [[commensalism|commensal]]s of animals. In 1875, [[Fedor Lösch]] described the first proven case of  [[amoebic dysentery]] in St. Petersburg, Russia. He referred to the amoeba he observed microscopically as ''Amoeba coli''; however, it is not clear whether he was using this as a descriptive term or intended it as a formal taxonomic name.<ref>{{cite journal | last1 = Lösch | first1 = F | year = 1875 | title = Massenhafte Entwickelung von Amöben im Dickdarm | url =https://zenodo.org/record/1428378 | journal = Virchows Archiv | volume = 65 | issue = 2| pages = 196–211 | doi=10.1007/bf02028799| s2cid = 6297817 }}</ref> The genus ''Entamoeba'' was defined by Casagrandi and Barbagallo for the species ''[[Entamoeba coli]]'', which is known to be a [[commensalism|commensal]] organism.<ref>*{{cite journal | last1 = Casagrandi | first1 = O. | last2 = Barbagallo | first2 = P. | year = 1895 | title = Ricerche biologiche e cliniche sull' ''Amoeba coli'' (Lösch). (Nota preliminare) | journal = Bollettino delle Sedute della Accademia Gioenia di Scienze Naturali in Catania | volume = 39 | page = 4 }}</ref> Lösch's organism was renamed ''[[Entamoeba histolytica]]'' by [[Fritz Schaudinn]] in 1903; he later died, in 1906, from a self-inflicted infection when studying this amoeba. For a time during the first half of the 20th century the entire genus ''Entamoeba'' was transferred to ''[[Endamoeba]]'', a genus of amoebas infecting invertebrates about which little is known. This move was reversed by the International Commission on Zoological Nomenclature in the late 1950s, and ''Entamoeba'' has stayed 'stable' ever since.

==Species==
Several species are found in humans and animals.  ''Entamoeba histolytica'' is the pathogen responsible for invasive '[[amoebiasis]]' (which includes amoebic [[dysentery]] and [[amoebic liver abscess]]es). Others such as ''[[Entamoeba coli]]'' (not to be confused with ''[[Escherichia coli]]'') and ''[[Entamoeba dispar]]''<ref>{{cite journal |vauthors=Diamond LS, Clark CG|title=A redescription of Entamoeba histolytica Schaudinn, 1903 (emended Walker, 1911) separating it from Entamoeba dispar Brumpt, 1925 |journal=Journal of Eukaryotic Microbiology |volume=40 |issue=3 |pages=340–344 |year=1993  |pmid=8508172 |doi=10.1111/j.1550-7408.1993.tb04926.x|s2cid=46363085 |url=https://zenodo.org/record/1230681 }}</ref> are harmless.  With the exception of ''[[Entamoeba gingivalis]]'', which lives in the mouth, and  ''E. moshkovskii'', which is frequently isolated from river and lake sediments, all ''Entamoeba'' species are found in the [[intestine]]s of the animals they infect. ''[[Entamoeba invadens]]'' is a species that can cause a disease similar to ''E. histolytica'' but in reptiles.  In contrast to other species, ''E. invadens'' forms cysts in vitro in the absence of bacteria and is used as a model system to study this aspect of the life cycle. Many other species of ''Entamoeba'' have been described, and it is likely that many others remain to be found.

==Structure==
[[File:Parasite130116-1-olm Entamoeba gingivalis microscopy.tif|thumb|left|''Entamoeba gingivalis'']]

''Entamoeba'' cells are small, with a single [[cell nucleus|nucleus]] and typically a single [[Pseudopod#Morphology|lobose pseudopod]] taking the form of a clear anterior bulge. They have a simple life cycle. The trophozoite (feeding-dividing form) is approximately 10-20 μm in diameter and feeds primarily on bacteria. It divides by simple binary fission to form two smaller daughter cells.  Almost all species form cysts, the stage involved in transmission (the exception is ''[[Entamoeba gingivalis]]''). Depending on the species, these can have one, four or eight nuclei and are variable in size; these characteristics help in species identification.

==Classification==
''Entamoeba'' belongs to the [[Archamoebae]], which like many other anaerobic eukaryotes have reduced [[mitochondrion|mitochondria]].<ref>{{cite journal |vauthors=Tovar J, Fischer A, Clark CG | title = The mitosome, a novel organelle related to mitochondria in the amitochondrial parasite Entamoeba histolytica | year = 1999| journal = Molecular Biology | volume = 32 | issue = 5 | pages = 1013–1021 | doi =10.1046/j.1365-2958.1999.01414.x | pmid = 10361303 |doi-access=free}}</ref> This group also includes ''[[Endolimax]]'' and ''[[Iodamoeba]]'', which also live in animal intestines and are similar in appearance to ''Entamoeba'', although this may partly be due to convergence.  Also in this group are the free-living amoebo-flagellates of the genus ''Mastigamoeba'' and related genera.<ref>{{cite journal |vauthors=Stensvold CR, Lebbad M, Clark CG |title=Last of the human protists: the phylogeny and genetic diversity of Iodamoeba. |journal=Molecular Biology and Evolution |volume=  29|pmid= 21940643 |doi=10.1093/molbev/msr238 |issue=1 |date=January 2012 |pages=39–42|url=http://researchonline.lshtm.ac.uk/28327/1/28327.pdf |doi-access=free }}</ref> Certain other genera of symbiotic amoebae, such as ''Endamoeba'', might prove to be synonyms of ''Entamoeba'' but this is still unclear.

==Culture==

===Fission===
Studying ''Entamoeba invadens'', [[David Biron]] of the [[Weizmann Institute of Science]] and coworkers found that about one third of the cells are unable to separate unaided and recruit a neighboring amoeba (dubbed the "midwife") to complete the fission.<ref>{{cite journal |vauthors=Biron D, Libros P, Sagi D, Mirelman D, Moses E | title = Asexual reproduction: 'Midwives' assist dividing amoebae | year = 2001 | journal = Nature | pmid = 11260701 | volume = 410 | issue = 6827 | pages = 430 | doi = 10.1038/35068628 | bibcode = 2001Natur.410..430B | doi-access = free }}</ref> He writes:

:''When an amoeba divides, the two daughter cells stay attached by a tubular tether which remains intact unless mechanically severed.  If called upon, the neighbouring amoeba midwife travels up to 200 μm towards the dividing amoeba, usually advancing in a straight trajectory with an average velocity of about 0.5 μm/s.  The midwife then proceeds to rupture the connection, after which all three amoebae move on.''

They also reported a similar behavior in ''[[Dictyostelid|Dictyostelium]]''.<ref>{{Cite journal | doi=10.1002/cm.20311| pmid=18688845|title = Chemotaxis-mediated scission contributes to efficient cytokinesis in Dictyostelium| journal=Cell Motility and the Cytoskeleton| volume=65| issue=11| pages=896–903|year = 2008|last1 = Nagasaki|first1 = Akira| last2=Uyeda| first2=Taro Q. P.}}</ref>

Since ''E. histolytica'' does not form cysts in the absence of bacteria, ''E. invadens'' has become used as a model for encystation studies as it will form cysts under axenic growth conditions, which simplifies analysis.<ref>{{Cite journal|last1=Rawat|first1=Aadish|last2=Singh|first2=Parikshit|last3=Jyoti|first3=Anupam|last4=Kaushik|first4=Sanket|last5=Srivastava|first5=Vijay Kumar|date=2020-04-30|title=Averting transmission: A pivotal target to manage amoebiasis|url=https://www.ncbi.nlm.nih.gov/pubmed/32356312|journal=Chemical Biology & Drug Design|volume=96|issue=2|pages=731–744|doi=10.1111/cbdd.13699|issn=1747-0285|pmid=32356312|s2cid=218475533}}</ref> After inducing encystation in ''E. invadens'', DNA replication increases initially and then slows down. On completion of encystation, predominantly tetra-nucleate cysts are formed  along with some uni-, bi- and tri-nucleate cysts.<ref>{{cite journal |vauthors=Singh N, Bhattacharya S, Paul J | title = Entamoeba invadens: Dynamics of DNA synthesis during differentiation from trophozoite to cyst | year = 2010 | pages = 329–33 | issue = 2 | volume = 127 | journal = Experimental Parasitology | pmid = 20727884 | doi = 10.1016/j.exppara.2010.08.013  }}</ref>

==Differentiation and cell biology==
[[Uninucleate]]d trophozoites convert into cysts in a process called encystation. The number of nuclei in the cyst varies from 1 to 8 among species and is one of the characteristics used to tell species apart. Of the species already mentioned, ''Entamoeba coli'' forms cysts with 8 nuclei while the others form tetra-nucleated cysts. Since ''E. histolytica'' does not form cysts ''in vitro'' in the absence of bacteria, it is not possible to study the differentiation process in detail in that species. Instead the differentiation process is studied using ''E. invadens'', a reptilian parasite that causes a very similar disease to ''E. histolytica'' and which can be induced to encyst ''in vitro''. Until recently there was no genetic transfection vector available for this organism and detailed study at the cellular level was not possible. However, recently a transfection vector was developed and the transfection conditions for ''E. invadens'' were optimised which should enhance the research possibilities at the  molecular level of the differentiation process.<ref>{{cite journal|last=Singh|first=Nishant |author2=Ojha, Sandeep |author3=Bhattacharya, Alok |author4=Bhattacharya, Sudha|title=Establishment of a transient transfection system and expression of firefly luciferase in ''Entamoeba invadens''|journal=Molecular and Biochemical Parasitology|date=2012 |volume=183|issue=1|pages=90–93|doi=10.1016/j.molbiopara.2012.01.003|pmid=22321531 }}</ref><ref>{{cite journal|last=Singh|first=Nishant |author2=Ojha, Sandeep |author3=Bhattacharya, Alok |author4=Bhattacharya, Sudha|title=Stable transfection and continuous expression of heterologous genes in ''Entamoeba invadens''|journal=Molecular and Biochemical Parasitology|date=2012 |volume=184|issue=1|pages=9–12|doi=10.1016/j.molbiopara.2012.02.012|pmid=22426570 }}</ref>

==Meiosis==

In sexually reproducing [[eukaryote]]s, [[homologous recombination]] (HR) ordinarily occurs during [[meiosis]].  The meiosis-specific [[recombinase]], [[DMC1 (gene)|Dmc1]], is required for efficient meiotic HR, and Dmc1 is expressed in ''E. histolytica''.<ref name=Kelso>{{cite journal |vauthors=Kelso AA, Say AF, Sharma D, Ledford LL, Turchick A, Saski CA, King AV, Attaway CC, Temesvari LA, Sehorn MG |title=Entamoeba histolytica Dmc1 Catalyzes Homologous DNA Pairing and Strand Exchange That Is Stimulated by Calcium and Hop2-Mnd1 |journal=PLOS ONE |volume=10 |issue=9 |pages=e0139399 |year=2015 |pmid=26422142 |pmc=4589404 |doi=10.1371/journal.pone.0139399 |bibcode=2015PLoSO..1039399K |doi-access=free }}</ref>  The purified Dmc1 from ''E. histolytica'' forms [[Synapsis|presynaptic]] filaments and catalyzes [[Adenosine triphosphate|ATP]]-dependent [[Homologous recombination|homologous DNA pairing]] and DNA strand exchange over at least several thousand [[base pair]]s.<ref name=Kelso />  The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1.<ref name=Kelso />  These processes are central to meiotic recombination, suggesting that ''E. histolytica'' undergoes meiosis.<ref name=Kelso />

Studies of  ''E. invadens'' found that, during the conversion from the [[Ploidy|tetraploid]] uninucleate [[Apicomplexan life cycle#Glossary of cell types|trophozoite]] to the tetranucleate cyst, [[homologous recombination]] is enhanced.<ref name=Singh>{{cite journal |vauthors=Singh N, Bhattacharya A, Bhattacharya S |title=Homologous recombination occurs in Entamoeba and is enhanced during growth stress and stage conversion |journal=PLOS ONE |volume=8 |issue=9 |pages=e74465 |year=2013 |pmid=24098652 |pmc=3787063 |doi=10.1371/journal.pone.0074465 |bibcode=2013PLoSO...874465S |doi-access=free }}</ref>  Expression of genes with functions related to the major steps of meiotic recombination also increased during encystations.<ref name=Singh />  These findings in ''E. invadens'', combined with evidence from studies of  ''E. histolytica'' indicate the presence of meiosis in the ''Entamoeba''.

== References ==
{{Reflist}}

==External links==
{{Wikispecies}}
{{Commons category}}
* [https://web.archive.org/web/20090517094121/http://homepages.lshtm.ac.uk/entamoeba/ ''Entamoeba'' Homepage]
* [https://web.archive.org/web/20080427061424/http://pathema.jcvi.org/cgi-bin/Entamoeba/PathemaHomePage.cgi Pathema-''Entamoeba'' Resource]
* [http://amoebadb.org/amoeba/''Entamoeba'' Genome Database] at [[AmoebaDB]]

{{Amoebozoa}}
{{Taxonbar|from=Q518891}}
{{Authority control}}

[[Category:Amoebozoa genera]]
[[Category:Parasitic amoebozoa]]
[[Category:Conosa]]