A Glossary of Terms Applied to Amoebae  

For additional information on general cell biology, see The Dictionary of Cell Biology.  Many terms used to describe the morphology of amoebae have been catalogued and explained by Smirnov & Goodkov, 1999.

Smirnov, A.V. & Goodkov, A.V. (1999). "An illustrated list of basic morphotypes of Gymnamoebia (Rhizopoda, Lobosea)." Protistology 1, 20-29.

Amitochondrial

A cell that lacks mitochondria. It has been understood that amitochondrial amoebae represent more primitive (early branching) forms, however Entamoeba which was for a very long time thought to lack mitochondria was then thought to have lost them secondarily (Clark & Roger, 1995), and finally now appears to possess mitochondria -like vesicles. Also, the genus Mastigamoeba was thought to have primitive features as it was assumed to be amitochondrial, however both SSUrDNA analysis (Sogin et al, 1996), and DNA polymerase sequence analysis (Stiller et al, 1998), indicate that this genus is not   primitive.  Another amitochondrial genus Psalteromonas branches within the order Percolozoa but this genus possess hydrogenosomes possibly as an adaptation to its micro-aerobic environment.

Clark, C.G. & Roger, A.J. (1995)."Direct evidence for secondary loss of mitochondria in Entamoeba histolytica." PNAS 92: 6518-6521.

Axenic

Cultured without any other organism. For example as a broth that sustains growth of the protist.  Many amoebae have been brought into axenic culture although to date (with the possible exception of Trichospherium, which is actually a testate amoeba) no marine gymnamoebae has been successfully brought to axenic condition. [More]

Bothrosome

A membranous invagination of the nuclear envelope described in Labyrinthula.

Porter, D. (1972). "Cell division in the marine slime mold, Labyrinthula sp.,and the role of the bothrosome in extracellular production." Protoplasma 74: 427-448.

Bacteria (and other cells) tend to adhere to and gather on surfaces.  Adhering to surfaces allows communities of bacteria to build up to their mutual advantage, each bacterial species may contribute biochemically to the whole.  There are advantages to be gained even for a single species as quorum sensing (see below) is enhanced that allows the bacteria to respond appropriately to the conditions.  Amoebae too are hugely advantaged in biofilms as the bacteria are concentrated on a surface along which they can move consuming the bacteria as they go.  Amoeboid locomotion only makes sense if they have a surface on which to crawl and many species such as Vannella seem to have evolved a shape specifically designed to maximise the frequency of collision with bacteria presented on a surface being so spread out.  Amoeba and other protist generally grow faster on surfaces compared to in suspension (Zubkov & Sleigh, 2000). Amoeba are found at their greatest numbers in biofilms for example in dental units (Barbeau & Buhler, 2001) or the surface of sea ice (Mayes et al, 1998).

Barbeau, J. & Buhler, T. (2001) Biofilms augment the number of free-living amoebae in dental unit waterlines., Res. Microbiol. 152, 753-760.

Mayes, D. F., Rogerson, A., Marchant, H. J. & Laybourn-Parry, J. (1998) Temporal abundance of naked bactivore amoebae in coastal east Antarctica.  Estuarine, Coastal & Shelf Sci. 46, 565-572.

Zubkov, M. V. & Sleigh, M. A. (2000) Comparison of growth efficiencies of protozoa growing on bacteria deposited on surfaces and in suspension. J.Eukaryot.Microbiol. 47, 62-69.

Contractile Vacuole

The "kidney " of the protozoans.  Its function is to pump out excess water from the cytoplasm of amoeba, they are most prominent and active in freshwater amoebae as marine amoebae are closer to isotonicity with seawater that freshwater.  The behaviour of the C.V. has been argued to have some use as a diagnostic tool for the classification of amoeba (Patterson, 1981), see T. quadrilineata in Thecamoeba.  The contractile force behind the emptying C.V. is strongly suspected of being generated by Myosin Ic, a molecular motor that works in conjunction with actin (see CS, and Myosin pages).  Antibodies against Acanthamoeba castellanii (Neff strain) myosin Ic were introduced that were known to block its activity in vitro, this lead to the immediate swelling of the amoeba until it burst!!).

Patterson, D.J. (1981). "Contractile vacuole complex behaviour as a diagnostic character for free-living amoebae." Protistologica 17, 243-248.

Endoplasmic reticulum 

(E.R.)

An extended membranous organelle that proteins destined for the cell membrane or for export are synthesized within (or on).  These proteins are extruded into the lumen of the E.R. as they are synthesized by ribosomes bound to docking proteins on the cytoplasmic surface.  The proteins are then modified by glycosylation and other post translational modification in the Golgi Apparatus.

Euryhaline

Tolerant of a wide range of salinity [Greek euyrs = wide & hals = salt].  Whereas most amoebae are either found in freshwater or marine waters, some e.g. Acanthamoeba are to be found occasionally in both.  In the case of Acanthamoeba the presence of encysted cells complicates matters as it is likely that they survive as cysts in the seas having been deposited there by natural or un natural means.  Other amoebae are however known to have the ability to survive in both environments and to make rapid accommodations (Oshima et al, 1986).  

References:-

Oshima, N., Takeda, F., & Ishii, K. (1986). " Responses of freshwater amoebae to salinity changes." Comp.Biochem.Physiol. 85a, 395-399.

Fabellate

A flattened, fan shape adopted by several amoeba genera such as Vannella, Platyamoeba, Flabellula, Flamella etc.  As one observes these amoeba gliding across a surface it seems that these cells are covering as much of the area as possible in order to encounter as many bacteria concentrated by adhesion on the biofilm.  This may well be true but several other cell types have also adopted this morphology, e.g. fish keratinocytes, the sperm of certain nematodes.

Glycocalyx

The glycoprotein component of the cell membrane. In some genera (e.g. Vannella), the glycoproteins are arranged into extended glycostyles.

Golgi

Also known as dictysome in older literature.  The Golgi or Golgi apparatus is an organelle whose function it is to add saccharides to glycoproteins.  The Golgi is typically formed into a stack of membranes, in mammalian cells these are arranged on microtubules close to the nuclear envelope.  Many amoebae do not produce recognisable Golgi but instead a series of unspecialised looking vesicles perform the function (e.g. Entamoeba, Ghosh et al, 1999).  There is a tendency for amoebae with well developed glycocalyx to have Golgi with distinct stacks, while those with a thin glycocalx do not. [More]

Ghosh, S. K., J. Field, J., Frisardi, M., Rosenthal, B., Mai, Z., Rogers, R. & Samuelson, J.  (1999). “Chitinase Secretion by Encysting Entamoeba invadens and Transfected Entamoeba histolytica Trophozoites: Localization of Secretory Vesicles, Endoplasmic Reticulum, and Golgi Apparatus.” Infect. Immun. 67(6), 3073-3081.

Gymnamoebae

This term seems to be applied to different groups of amoeba by different authors.  Gymnamoebae usually means naked amoebae as distinct from testate amoebae.

Hydrogenosomes

Modified mitochondria that perform a similar function to mitochondria under anoxic conditions.

Seal, D. V. (1994) Acanthamoeba keratitis: a problem for contact lens users that is here to stay. Br.Med.J. 308, 1116-1117.

Lanceolate

Flattened lance shaped e.g Paradermamoeba

Mastigote

An alternative name for the eukaryote flagella.  Mastigote is the preferred term of some authors in order to prevent confusion with the prokaryote flagella that is a very different structure.  [More]

Microtubule

Microtubules are a component of the cytoskeleton composed of the tubulin proteins a- and b- tubulin. [More]

Mitochondria

A cellular organelle that originated as a gram negative endosymbiotic bacteria.  Mitochondria have retained a remnant of their once intact bacterial genome.  The entire mitochondrial genome has been sequenced in  Acanthamoeba and Dictyostelium, however attempts to use mitochondrial sequences to classify members of the genus Acanthamoeba have not been completely successful.   Mitochondria produce ATP using a chemiosmotic mechanism involving electron transport.  The morphology of mitochondria has been extensively used as a means of classifying amoeba, however it has recently come to light that a single protein (ATP synthetase) determines the morphology of the entire organelle (Paumard et al, 2002), making the classification scheme fragile .

Paumard, P., Vaillier, J., Coulary, B., Schaeffer, J., Soubannier, V., Mueller, D. M., Brethes, D., di Rago, J.-P. & Velours, J. (2002) The ATP synthase is involved in generating mitochondrial cristae morphology., EMBO J. 21, 221-230.

Monoaxenic

Living in culture with a single species on prey species.  Many small amoebae are capable of living in monoaxenically with E.coli. 

Akins, R. A., Gozs, S. M. & Byers, T. J. (1985) Factors regulating the encystment enhancing activity (EEA) of Acanthamoeba castellanii, J.Gen.Microbiol. 131, 2609-2617.

Byers, T. J., Kim, B. G., King, L. E. & Hugo, E. R. (1991) Molecular aspects of the cell cycle and encystment of Acanthamoeba, Rev.Infect.Diseases. 13, S373-S-384.

SSUrDNA

Genes encoding the Small subunit ribosomal RNA, used extensively to establish relationships between groups of organisms.  

Trichocyst