color = #FFC8A0
name = "Entamoeba"
genus = "Entamoeba"
subdivision_ranks = Species
"Entamoeba" is a
genusof Amoebozoafound as internal parasites or commensals of animals. Several species are found in humans. " Entamoeba histolytica" is the pathogen responsible for " amoebiasis" (which includes amoebic dysenteryand amoebic liver abscesses), while others such as " Entamoeba coli" and "E. dispar" 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 intestines of the animals they infect.
"Entamoeba" cells are small, with a single nucleus and typically a single 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 "E. gingivalis"). Depending on the species, these can have one, four or eight nuclei and are variable in size; these characteristics help in species identification.
"Entamoeba" belongs to the
Archamoebae, which are unusual in lacking mitochondria. This group also includes " Endolimax", which also lives in animals and is similar in appearance to "Entamoeba", although this may partly be due to convergence. Certain other genera of symbiotic amoebae, such as "Endamoeba", might prove to be synonyms of "Entamoeba" but this is still unclear.
Studying "Entamoeba invadens",
David Bironof the Weizmann Institute of Scienceand 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. [cite journal | author = Biron D, Libros P, Sagi D, Mirelman D, Moses E | title = Asexual reproduction: 'Midwives' assist dividing amoebae | year = 2001 | journal = Nature | volume = 410 | pages = 430 | doi = 10.1038/35068628 | url = http://www.nature.com/nature/journal/v410/n6827/full/410430a0.html] 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 "Dictyostelium".
* [http://homepages.lshtm.ac.uk/entamoeba/"Entamoeba" Homepage]
* [http://pathema.jcvi.org/cgi-bin/Entamoeba/PathemaHomePage.cgi Pathema-"Entamoeba" Resource]
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