amoeba

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amoeba:

see amebaameba
or amoeba
, common name for certain one-celled organisms belonging to the phylum Sarcodina of the kingdom Protista. Amebas were previously classified as members of the animal kingdom.
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Amoeba

 

the order of the simplest organized protozoa of the class Sarcodina. Most live in fresh waters, a few in the soil; there are parasitic forms. They are usually of microscopic dimensions up to 50 μm, but there are also “giants” such as Pelomyxa, which grows to 2–3 mm. Amoebas have no constant body shape; their cytoplasmic body forms extrusions or pseudopodia which aid in motion and food gathering. They feed on bacteria, minute algae, and protozoa. The amoeba engulfs the food particle and from its cytoplasm the amoeba secretes digestive juices and forms a food vacuole within which the food is dissolved and is incorporated into the cytoplasm. The excretion of water (osmoregulation) and metabolic products occurs through the contractory vacuoles, which gradually accumulate waste matter and discharge it at the surface.

Amoebas ordinarily have one nucleus, but Pelomyxa is multinucleate. The majority of amoebas multiply asexually, dividing in two. The division of the body is preceded by mitosis in the nucleus. A sexual process is known only in very rare cases.

Upon subjection to unfavorable conditions—for instance, insufficient food, cold, or drying of the water body—the amoeba’s body becomes round and the surface of its cytoplasm becomes a dense protective layer; a cyst forms that is resistant to unfavorable effects of the dormant stage. Freshwater amoebas can serve as a water pollution index. Parasitic amoebas live in the intestines of various animals and man. Among these the most harmful is the dysentery amoeba (Entamoeba histolytica), which produces a severe form of amoebic dysentery in man. Infection occurs via cysts, which remain viable outside the human body.

REFERENCES

Dogel’, V. A., Iu. I. Polianskii, and E. M. Kheisin. Obshchaia protozoologiia. Moscow-Leningrad, 1962.
Seravin, L. N. Dvigatel’nye sistemy prosteishikh. Leningrad, 1967.

A. A. STRELKOV

Amoeba

[ə′mē·bə]
(invertebrate zoology)
A genus of naked, rhizopod protozoans in the order Amoebida characterized by a thin pellicle and thick, irregular pseudopodia.

amoeba

(US), ameba
any protozoan of the phylum Rhizopoda, esp any of the genus Amoeba, able to change shape because of the movements of cell processes (pseudopodia). They live in fresh water or soil or as parasites in man and animals

Amoeba

(operating system)
A distributed operating system developed by Andrew S. Tanenbaum and others of Vrije Universiteit, Amsterdam. Amoeba is only available under licence from the VUA, but is free of charge and includes all source, binaries and documentation.

http://am.cs.vu.nl/.

Amoeba

(computer, abuse)
A derogatory term for Commodore's Amiga personal computer.
References in periodicals archive ?
Case definitions for non-notifiable infections caused by free-living amebae (Naegleria fowleri, Balamuthia mandrillaris, and Acanthamoeba spp.
Experimental animal studies demonstrate the dilation of hepatic sinusoids containing amebae surrounded by polymorphonuclear leukocytes (PMNs) within 3 hours after embolization of trophozoites into the mesenteric-splanchnic circulation.
Unlike other free-living amebae, which are typically found in fresh water, the natural reservoir for Balamuthia amebae is believed to be the soil.
However, mixed keratitis caused by amebae in association with ameba-resistant pathogens is rarely seen.
In 2003, mimivirus was isolated from a water cooling tower in Bradford, UK, after a pneumonia outbreak and was reported to infect Acanthamoeba polyphaga amebae (2).
Found worldwide in moist soil and freshwater, these amebae proliferate during summer when ambient temperature increases.
The myxamoebae were seen after 24 hours, and the amebae had transformed into microcysts after 48 hours of incubation.
Increasing evidence indicates that these obligate intracellular bacteria infecting free-living amebae may cause respiratory diseases in humans (1).
To confirm the presence of free-living amebae (FLA) DNA, we used PCR with forward primer PFLAF: 5'-CGCGGTAATTCCAGCTCCAATAGC-3' and reverse primer P-FLA-R: 5'-CAGGTTAAGGTCTCGTT CGTTAAC-3' targeted at conserved stretches of Acanthamoeba 18S rDNA (10).
To the Editor: Free-living amebae are ubiquitous protists able to endure extreme temperature and pH in diverse environments (1).