Phylogeny of diplomonads, retortamonads and oxymonads

Diplomonads, Retortamonads and Oxymonads are groups of amitochondriate anaerobic and mainly parasitic flagellates. Their parasitic representatives live in the intestine of wide range of hosts. All three groups are considered to be members of the phylum Metamonada.


One genus, Giardia, whose representatives cause serious illness of man and many animal species, was extensively studied in many respects. In the phylogenetic tree constructed on the basis of sequences of the small subunit rRNA, Giardia is placed at the very root of eukaryotic branch. It was widely discussed if this is real position of the species or an artefact caused by a long branch attraction effect. The ribosomal rRNA of this species has unusually high ratio of GC nucleotides so can be attracted in the tree to the bacterial sequences used as an outgroup. Small subunit rRNA from the species Hexamita inflata was sequenced later. Although the sequence has normal GC ratio, it was also placed at the root of eukaryotic branch. Analysis performed with sequences of many other genes (EF-1 alpha, EF-1 beta, alpha-tubulin etc.) also supports the antiquity of diplomonads. Recently, a gene coding the mitochondrial type of t-valyl-tRNA synthetase was found in the genome of Giardia . This finding suggested that Diplomonads were not primarily amitochondriate organisms as had been thought before, but that they lost their mitochondria secondarily. In our opinion it will be interesting to study in more detail the phylogenetical relationship of different genera of diplomonads and of the two main groups of diplomonads - Enteromonadina (regarded as phylogeneticaly more primitive) and Diplomonadina. We would like to acquire isolates of different diplomonad genera from nature, especially isolates of species from the group Enteromonadina, and on the basis of sequences of their genes construct the phylogenetical tree of this group.

Retortamonads and Oxymonads

These groups of protist are much less studied in comparison with diplomonads. As far as we know only two molecular phylogenetical studies were published. In these studies authors sequenced the gene for EF-1alpha of species Dinenympha exilis (Oxymonadida) (Moriya et al., 1998) and genes for alpha-tubulin and of Dinenympha exilis and Pyrsonympha grandis (Oxymonadida) (Moriya et al., 2001). The phylogenetic analysis was performed with these sequences indicated that these protists branch of after the diplomonad clade as an independent lineage of early branching organisms. No other gene of these organisms was sequenced, therefore the question of their evolutionary position cannot be considered to be satisfactorily answered. Both groups include amitochondrial protist and it is still not proved with certainity if their amitochondrial state is primary or secondary, i.e. whether they either never had mitochondria or they once possessed mitochondria but lost it during evolution. Many species of retortamonads were described from many host species. Some of them are morfologically not easily distinguishable and so it is not known if they are really separate species. Phylogenetical relations of retortamonadid species and their host specifity or nonspecifity were not studied by molecular methods at all. In our research we want to adress some of these interesting questions. Up to now we isolated several strains of Retortamonas sp. from different host species and one strain of Monocercomonoides sp. (Oxymonadida) from cow. We plan to sequence the gene for 16S rRNA in these organisms and to look for mitochondrial genes in their genome.


Moriya S, Ohkuma M, Kudo T Phylogenetic position of symbiotic protist Dinemympha exilis in the hindgut of the termite Reticulitermes speratus inferred from the protein phylogeny of elongation factor 1 alpha. GENE 210: (2) 221-227 APR 14 1998

Moriya S, Tanaka K, Ohkuma M, et al. Diversification of the microtubule system in the early stage of eukaryote evolution: Elongation factor 1 alpha and alpha-tubulin protein phylogeny of termite symbiotic oxymonad and hypermastigote protists. J MOL EVOL 52: (1) 6-16 JAN 2001