Morphological and molecular diversity of the monocercomonadid

Morphological and molecular diversity of the monocercomonadid genera Monocercomonas, Hexamastix and Honigbergiella gen. nov 1 Morphological and molecular diversity of the monocercomonadid genera Monocercomonas, Hexamastix and Honigbergiella gen. nov. ABSTRACT Family Monocercomonadidae (Parabasala, Trichomonadida) is characterized by the absence of a costa and in most species also of an undulating membrane, both of which are typical structures of trichomonadids. We have examined 25 isolates of Monocercomonadidae species by sequencing of SSU rDNA and ITS region and by light and transmission electron microscopy. The isolates formed three distinct phylogenetically unrelated clades: 1) Monocercomonas colubrorum, 2) Monocercomonas ruminantium together with a strain ATCC 50321 designed as Pseudotrichomonas keilini and 3) Hexamastix. Twenty isolates of Monocercomonas colubrorum divided into three clades with no host-specificity. The morphological differences among clades were insufficient to classify them as a separate species. Non-monophyly of the cattle commensal Monocercomonas ruminantium with the type species Monocercomonas colubrorum and absence of Pseudotrichomonas characters in the free-living strain ATCC 50321 led to their reclassification into a new genus (Honigbergiella gen. nov.). The close relationship of these strains indicates a recent switch between a free-living habit and endobiosis. Two strains of Hexamastix represented different species – Hexamastix kirbyi Honigberg 1955 and Hexamastix mitis sp. nov. Polyphyly of Monocercomonadidae confirmed that the absence of costa and undulating membrane are not taxonomically significant characters and were probably secondarily lost in some or all clades. Our observations, however, indicated that other characters – infrakinetosomal body, comb-like structure, marginal lamella and the type of axostyle – are fully consistent with the position of Monocercomonadidae species in the parabasalian tree and are, therefore, reasonable taxonomic characters.