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A Microbial Biorealm page on the Pelobionta

Mastigamoeba longfilum. Protist Information Server


Higher order taxa



Mastigamoeba balamuthi
Pelomyxa palustris
Pelomyxa corona

NCBI: Taxonomy Genome

Description and Significance

Pelobionta, also known as karyoblasteans, are an amitochondriate amoeboflagellate group, and it has been suggested that they are early eukaryotes. However, placing Pelobionta in a phylogenetic category has proved complicated. While their cytologic features make them appear ancient, rDNA analysis does not place them on early branches. They are large amoebae. Pelobionta are free-living organisms. A new species, Pelomyxa corona, was discovered in 2004 (Frolov et. al.).

Genome Structure

There are multiple species withing Pelobionta, and therefore this classification has many different genome structures. For example, the small subunit ribosomal RNA of the Pelobionta species Pelomyxa palustris is exceptionally long. Analysis of rRNA in P. palustris and other species suggests that Pelobionta emerged after other protists.

Cell Structure and Metabolism

Pelobionta do not have mitochondria. They also lack stacked dictyosomes. Pelobionta are cylindrical in shape. The species Mastigamoeba balamuthi lacks Golgi bodies. However, this does not mean that they lack structures that will perform similar functions. Dacks et. al. (2003) found genes within this species that are homologus to the retromer, coatomer and adaptin complexes, which are related to Golgi bodies. Pelobionta have non-motile flagella whose function is poorly understood; motility is based on pseudopods. The species Mastigamoeba schizophrenia has paired nuclei and basal bodies that lack triplets.

Pelobionta are heterotrophs, feeding on bacteria and small protists.

Pelobionta reproduction incorporates both mitosis and binary fission. The nuclear membrane remains intact throughout division. Duplication produces two chromatids. Then, the microtubule organizing center (MTOC) divides, and microtubules assemble along the new MTOCs. Finally, the cells split.

Nuclear division in Pelobionta.Symbiosis and Origin of Eukaryotes


Pelomyxa palustris. Photo by Wim van Egmond.

Pelobionta form symbiotic relationships with bacteria; the bacteria serve as a substitute for mitochondira. It is believed that this lack of mitochondria is a secondary absence. There are three different relationships in Pelomyxa species. One bacteria detoxifies oxygen, one metabolizes it, and one removes cellular waste. Pelobionta are able to survive in low-oxygen environments. They are freshwater organisms, and can often be found living in mud. Geographically, Peolbionta are located in temperate regions of the Northern Hemisphere, most commonly in North America. A few species, such as Mastigamoeba balamuthi, are parasites.


Arisue N, Hashimot T, Lee JA, Moore DV, Gordon P, Sensen CW, Gaasterland T, Hasegawa M, Muller M. "The phylogenetic position of the pelobiont Mastigamoeba balamuthi based on sequences of rDNA and translation elongation factors EF-1alpha and EF-2." J Eukaryot Microbiol. 2002 Jan-Feb;49(1):1-10.

Bapteste, Eric et. al. "The analysis of 100 genes supports the grouping of three highly divergent amoebae: Dictyostelium, Entamoeba, and Mastigamoeba." PNAS. February 5, 2002; 99(3):1414-1419.

Dacks, Joel B. et. al. "Evidence for Golgi bodies in proposed 'Golgi-lacking' lineages." Proceedings of the Royal Society London. 2003;270:168-171.

Edgcomb, Virginia P. et. al. "Pelobionts are Degenerate Protists: Insights from Molecules and Morphology." Molecular Biology and Evolution. 2002;19:978-982.

Edgcomb, Virginia P. "Project Report: Eukaryotic Origins and the Evolution of Cellular Complexity - Eukaryotic rRNA Evolution: Early Diverging Eukaryotes."

Frolov, Alexander O., Ludmila V. Chystjakova, and Andrew V. Goodkov. "A new peliobont protist Pelomyxa corona sp. n. (Peloflagellata, Peliobontida)." Protistology. 2004;3(4):233-241.

Hoback, W. Wyatt. Evolution of Early Eukaryotes.

Messing, Charles Garrett. "Protazoa" Classification.

Millot, Jessica. First Eukaryotes.

Milyutina IA, Aleshin VV, Mikrjukov KA, Kedrova OS, Petrov NB. "The unusually long small subunit ribosomal RNA gene found in amitochondriate amoeboflagellate Pelomyxa palustris: its rRNA predicted secondary structure and phylogenetic implication." Gene. 2001 Jul 11;272(1-2):131-9.

Patterson, David J. Evolution: A Molecular Point of View.

Patterson, David J. "Parasitic Protists." The Tree of Life Web Project.

Protist Information Server.

Stiller JW, Duffield EC, Hall BD. "Amitochondriate amoebae and the evolution of DNA-dependent RNA polymerase II." Proc Natl Acad Sci U S A. 1998 Sep 29;95(20):11769-74.

Stiller JW, Hall BD. "Long-branch attraction and the rDNA model of early eukaryotic evolution." Mol Biol Evol. 1999 Sep;16(9):1270-9.

Symbiosis and Origin of Eukaryotes.

van Egmond, Wim. Amoebas are more than just blobs.

Waggoner, Ben. Introduction to the Basal Eukaryotes.