A Glossary of Terms Applied to Amoebae
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.
A.V. & Goodkov, A.V. (1999). "An illustrated list of basic
morphotypes of Gymnamoebia (Rhizopoda, Lobosea)." Protistology
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
C.G. & Roger, A.J.
(1995)."Direct evidence for secondary loss of mitochondria in Entamoeba
histolytica." PNAS 92: 6518-6521.
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]
invagination of the nuclear envelope described in Labyrinthula.
D. (1972). "Cell division in the marine slime mold, Labyrinthula
sp.,and the role of the bothrosome in extracellular production." Protoplasma
(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).
& 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,
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
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
this lead to the immediate swelling of the amoeba until it burst!!).
D.J. (1981). "Contractile vacuole
complex behaviour as a diagnostic character for free-living amoebae."
Protistologica 17, 243-248.
Becker, M., M.
Matzner, et al. (1999). “Drainin required for membrane fusion of the
contractile vacuole in Dictyostelium
is the prototype of a protein family also represented in man.” EMBO
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.
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).
N., Takeda, F., & Ishii, K. (1986). " Responses of freshwater
amoebae to salinity changes." Comp.Biochem.Physiol. 85a,
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.
glycoprotein component of the cell membrane. In some genera (e.g. Vannella),
the glycoproteins are arranged into extended glycostyles.
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]
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),
This term seems to be
applied to different groups of amoeba by different authors.
Gymnamoebae usually means naked amoebae as distinct from testate amoebae.
that perform a similar function to mitochondria under anoxic conditions.
An infection of the eye often caused by Acanthamoeba
pathogenesis. A protease secreted by the amoeba is important in the
development of the disease. See Acanthamoeba
Seal, D. V. (1994) Acanthamoeba keratitis:
a problem for contact lens users that is here to stay. Br.Med.J. 308,
Flattened lance shaped
These are proteins that
bind specifically to sugars or other carbohydrates, usually on other
proteins. Amoeba are known to produce lectins.
Literally slug-like, Another
term that is used differentially by different authors. Usually, the
term is applied to cylinder shaped amoeba such as Naegleria,Vahlkampfia,
Hartmannella, and Saccamoeba. The limax amoeba are not
necessarily related, as this morphology has been adopted by a number of
genera across the protists.
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]
Microtubules are a component
of the cytoskeleton composed of the tubulin proteins a- and
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 .
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,
in culture with a single species on prey species. Many small amoebae
are capable of living in monoaxenically with E.coli.
This term is usually used in connection with
bacteria but in principle at least the same phenomenon is likely to occur
in amoeba. Bacterial species secrete messenger molecules which
allows the colony to measure how many other bacteria of that species are
around so that genes may be switched on to benefit the whole colony.
Acanthamoeba performs a similar function. By the sensing the
onset of harsh conditions each member produces a molecule (not
characterised as yet) that encourages the formation of cysts in
neighbouring Acanthamoeba (Akins et
al, 1985; Byers
et al, 1991). In this way the
population is more likely to beat the race against time so that more
amoeba are able to encyst and so escape the bad times.
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,
Flattened branching cell extensions that fuse
leaving spaces between them e.g. Leptomyxa
encoding the Small subunit ribosomal RNA, used extensively to establish
relationships between groups of organisms.