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Classification of the Amoebae

Page updated 26/8/03

The classification of the amoebae has been fraught with ambiguity and confusion.   This is in part due to the fact that many of the group lack morphologically helpful features and the fact that so many protists from diverse origins have taken up the amoeboid way of life.  Fredrick Page (formerly of the Culture Collection of Algae and Protozoa) has brought some order to the classification of the amoeba in his heroic life-long study.  He has described dozens of amoebal species for the first time and his keys remain essential reading for those wishing to understand the amoeba both freshwater (Page, F.C., 1988) and marine (Page, F.C., 1983).  Ultimately, a thorough understanding of amoebal classification must include genetic data such as SSUrDNA sequencing.  Progress has been made along these lines for a variety of amoebal species and in particular Acanthamoeba and Naegleria (De Jonckheere's group).  However, even here difficulties and ambiguities have arisen, for example..   The assumption that the SSUrDNA analysis makes is that each protist has one unique sequence and that this has been inherited directly from its immediate parent with the occasional mutation.  It is known that at least one species of algae possesses two distinct SSUrDNA genes which of course complicates things!!  Some strains of Acanthamoeba contain at least two genes (Stothard et al, 1998), and some Neoparamoeba have more than three! (Fiala & Dykova 2003). It seems that for some groups notably the Vahlkampfiidae and Entamoebidae these genes are held on a multi-copy circular plasmid.  This introduces a fresh suspicion; can one plasmid (with its itinerant replication codes and promoters) be transmitted horizontally between members of these groups?  Even given that SSUrDNA analysis may not be perfect I believe that it is the best option open to us.  One advantage is that significant progress has already been made and many disparate amoeboid genera have had members sequenced.  If it turns out that there are significant problems with SSUrDNA analysis as a means to accredit relationships it will still serve at least one very tangible advantage this is that one determined there would be little future doubt that amoeba "A" is the same or similar to a fresh isolate.  As things stand in order to establish that a fresh isolate is a strain of a previous species takes an immense amount of work and considerable experience.  Take for example Rosculus ithacus, isolated from the rectum of a grass snake, and subsequently isolated from a river and a ditch in the Cambridge area later.  Despite painstaking efforts, the fact that the fresh strains possessed contractile vacuoles while the original did not leaves considerable doubt.  This would have been dissipated to a very large degree if the SSUrDNA of the original isolate had been  determined.  Of course this would have been very difficult back in 1963 when the poor snake was originally explored but now with PCR and sequencing by post this is almost trivial (if a little expensive for the budget of the average amoeba lab!).

It is now being appreciated that some groups of amoebae are emerging from the confusion:-


Acanthamoebidae Amoebidae Entamoebidae
Flabellulidae Gruberellidae The Heterolobosea Hyalodiscidae
Paramoebidae Pelomyxidae Thecamoebidae
The Vannellidae


Fiala, I. & Dykova, I. (2003) Molecular characterisation of Neoparamoeba strains isolated from gills of Scophthalmus maximus. Dis Aquat Organ. 55, 11-16.

Schaeffer, A. (1926) "Taxonomy of the amebas." Pap.Dept.Mar.Biol.Carnegie Institut. Wash. Vol XXIV, 1-116.

Sogin, M. L., Silberman, J.D, Hinkle, G. & Morrison, H.G. (1996). "Problems with molecular diversity in the eukarya.".Society of General Microbiology Symposium: Evolution of microbial Life ed.Roberts, D.M., Sharp, P., Alderson, G. & Collins, M.A. Cambridge University Press. pp167-184.

Stothard, D. R., Schroeder-Diedrich, J. M., Awwad, M. H., Gast, R. J., Ledee, D. R., Rodriguez-Zaragoza, S., Dean, C. L., Fuerst, P. A. & Byers, T. J. (1998) The evolutionary history of the genus Acanthamoeba and the identification of eight new 18S rRNA gene sequence types. J.Eukaryotic Microbiol. 45, 45-54.

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