Entamoeba
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Entamoeba coli |
Entamoeba is a genus of amoebozoa found as internal parasites or commensals of animals. Several species are found in humans. Entamoeba histolytica is the pathogen responsible for amoebic dysentery, while others such as Entamoeba coli and E. dispar are harmless. The cells are small, with a single nucleus and typically a single lobose pseudopod taking the form of a clear anterior bulge.
Entamoeba belongs to the Archamoebae, which are unusual in lacking mitochondria. This group also includes Endolimax, which also lives in animals and is very similar to Entamoeba, although this may partly be due to convergence. Several other genera of symbiotic amoebae, such as Endamoeba, are now considered synonyms of Entamoeba.
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. 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.
