Phylogeny of Spironucleus (Eopharyngia: Diplomonadida: Hexamitinae)

Diplomonad flagellates from the genera Spironucleus and Hexamita (Hexamitinae) inhabit the digestive tract of a variety of animal hosts, some as important pathogens, and others as commensals. Species descriptions of many diplomonads have been based on light microscopy only, causing many taxa to be misidentified. Presently, electron microscopy is considered the appropriate tool for description of diplomonads. The existence of morphologically very similar genotypes/species has in addition prompted the need for molecular tools to resolve the true identity of many diplomonad taxa. To further explore the relationship within the Hexamitinae we have sequenced most of the SSU rRNA gene from Spironucleus torosa isolated from Atlantic cod, Spironucleus meleagridis isolated from turkey, Spironucleus vortens isolated from ide and Hexamita nelsoni isolated from oyster. Phylogenetic analyses recovered three non-monophyletic Spironucleus clades that may have originated separately in the sea, in freshwater or on land. Spironucleus torosa was identified as a sister taxon to Spironucleus barkhanus and Spironucleus salmonicida. Spironucleus vortens from ide appeared to be genetically very different from Spironucleus vortens isolated from angelfish.