Acanthamoeba

Page updated 28/5/03

Acanthamoeba is perhaps the most common protist in soil. It is present in freshwater, soil (Sawyer, 1989) and can be isolated from marine environments (Sawyer, 1971; Sawyer et al, 1977; Page 1981) and even the air (Kingston & Warhurst, 1969), from the Arctic through the tropics (Bhattacharya et al, 1987) and into Antarctica (Mayes et al, 1989; Brown et al, 1982 ). The genus has been associated with human disease (see Acanthamoeba pathogenesis), and has a history of increasing our understanding of eukaryotes a a model organism, especially in the study of the cytoskeleton (see Acanthamoeba cytoskeleton).

Figure 2.  S.E.M. of Acanthamoeba castellanii . This amoeba is caught in the act of moving to the left. Note the presence of Acanthopodia, long, finger- like projections that arise from the leading edge and rise up and over the cell to be absorbed into the body as they move towards the rear of  the cell. This may be a feeding strategy that permits the amoeba to explore the region at the advancing front, or conceivably, it may be a way to increase the spatio-temporal gradient that is part of the chemotactic response.  During feeding bacteria are encountered by the leading edge where they adhere.  Adherent bacteria are often seen to remain in position relative to the substrate as the cell flows beneath, until they reach the uroid.  Large clumps of bacteria are often visible here and it is here that engulfment or phagocytosis is seen to take place.

(Image courtesy of Dr Steven Dobberstein)

As Acanthamoeba are ubiquitous and so abundant, is it hardly surprising that they have been connected with various human diseases.  Although these amoebae cause a very serious life threatening disease , this is exceptionally rare.  More common is keratitis, a disease associated with contact lens use and (more often), abuse.  Acanthamoeba together with several other amoeba are parasitised by various bacteria (Fig 2).  This is significant from the point of human health because one of these is Legionella, a bacterium that has caused serious outbreaks. Legionella, itself not a robust bacteria survives harsh conditions by becoming encased within the resistant cyst of Acanthamoeba and Hartmannella  (See Pathogenesis & Acanthamoeba).

Feeding
Acanthamoeba feeds on micro-organisms in bio-films, usually on surfaces (Brown & Barker, 1999) but even at the air-water interface (Preston et al, 2001).  The Acanthapodia, finger-like projections arising from the leading edge and transported over the cell surface rearwards may be involved in the feeding process by increasing surface area with which to capture suitable prey (Figure 1). Acanthamoeba detects prey items by chemotaxis (). Prey items are usually bacteria (Upadhyay et al, 1968; Weekers et al, 1993) but algae (Wright et al, 1981) yeast (Allen & Dawidowicz, 1990 ) and other protist are sometimes taken. 

Links:-

Acanthamoeba at the Protist Information Server

Thomas J. Byers  Acanthamoeba classification by SSUrDNA

Simon Kilvington Ecology & Pathogenicity of Acanthamoeba (and Naegleria)

Acanthamoeba mitochondria OGMP sequencing projects

Available strains:-

Other Topics:-

The cytoskeleton of Acanthamoeba	Classification of Acanthamoeba	Relationship to other Amoebae.
The phylogenetic position of Acanthamoeba	Legionella and Acanthamoeba	Pathogenesis and Acanthamoeba
Amoeboid locomotion	Molecular Biology of Acanthamoeba	Labs working with Acanthamoeba
Chemotaxis

References:-

Allen, P. G. & Dawidowicz, E. A. (1990) Phagocytosis in Acanthamoeba: 1. A mannose receptor is responsible for the binding and phagocytosis of yeast. J.Cell.Physiol. 145, 508-513.

Bhattacharya, A., Ghosh, M. & Bhattacharya, S. (1987) Seasonal abundance of Acanthamoeba rhysodes (Singh, 1952) (Protozoa: Gymnamoeba) in a mangrove litter-soil ecosystem of Gangetic-estuary, India. J.Prot. 34, 403-405.

Brown, M. R. W. & Barker, J. (1999) Unexplored reservoirs of pathogenic bacteria: protozoa and biofilms. Trends Microbiol. 7, 46-50.

Brown, T. J., Cursons, R. T. M. & Keys, E. A. (1982) Amoebae from Antarctic soil and water. Appl.Environmental Microbiol. 44, 491-493

Habte, M. & Alexander, M. (1978) Mechanisms of persistence of low numbers of bacteria preyed upon by protozoa. Soil Biol. Biochem. 10, 1-6.

Kingston, D. & Warhurst, D. C. (1969) Isolation of amoebae from the air. J.Med.Microbiol. 2, 27-36.

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.

Page, F. C. (1981) A light- and electron-microscopic study of Protoacanthamoeba caledonica n.sp., type-species of Protoacanthmaoeba n. g. (Amoebida, Acanthamoebidae)., J.Protozool. 28, 70-78.

Preston, T. M., Richard, H. & Wotton, R. S. (2001) Locomotion and feeding of Acanthamoeba at the water-air interface of ponds., FEMS letters. 194, 143-147.

Sawyer, T. K. (1971) Isolation and identification of free-living marine amoebae from upper Chesapeake bay, Maryland. Trans.Amer.Micros.Soc. 90, 43-51.

Sawyer, T. K. (1989) Free-living pathogenic and non-pathogenic amoebae in Maryland soils. App.Environ.Microbiol. 55, 1074-1077.

Sawyer, T. K., Visvesvara, G. S. & Harke, B. A. (1977) Pathogenic amoebas from brackish and oceanic sediments, with a description of Acanthamoeba hatchetti, n.s p., Science. 196, 1324-1325.

Upadhyay, J. M. (1968) Growth and bacteriolytic activity of a soil amoeba, Hartmannella glebae, J.Bacteriol. 95, 771-774. (This Hartmannella is actually an Acanthamoeba)

Weekers, P. H. H., Bodelier, P. L. E., Wijen, J. P. H. & Vogels, G. D. (1993) Effects of grazing by the free-living soil amoebae, Acanthamoeba catellanii, Acanthamoeba polyphaga, and Hartmannella vermiformis on various bacteria. App.Environ.Microbiol. 59, 2317-2319.

Wright, S. J. L., Redhead, K. & Maudsley, H. (1981) Acanthamoeba castellanii, a predator of cyanobacteria. J.Gen.Microbiol. 125, 293-300.