Just accepted: Gile and Slamovits – Phylogenetic position of Lophomonas striata Butschli (Parabasalia) from the hindgut of the cockroach Periplaneta americana. Protist, in press.
What’s the paper about?
Parabasalid protists are a very diverse but poorly known type of microbes. They include Trichomonas vaginalis, probably the only parabasalid known to non-specialists because it is a human parasite. One of the reasons why these organisms result so alien to our everyday perception is that they not usually found in plain sight. The other reason is that, well, some of them do look like aliens (photo right side). One of the places where parabasalids are frequently found is in the guts of wood-eating termites and cockroaches. Along with myriads of bacteria, archaea and other protists, hordes of parabasalids swarm the tummy of these beloved insects and help them eat chunks of wood without fearing an indigestion. The insect cannot digest cellulose on its own, but the microbial community that inhabit their gut breaks down the wood into useable nutrients with great efficiency, as the owners of termite-infested homes can attest.
Lophomonas striata is related to the wood-munching parabasalids but lives inside the less specialized, omnivorous house roach Periplaneta americana. Cells of L. striata are ovoid, about 20-40um long and 8-15um wide. At the anterior end there is a conspicuous tuft of at least 50 flagella (photo left side). Traditionally, the genus Lophomonas has been considered to be related to other genera of similar morphological characteristics such as Joenia and Kofoidia, and together form the family Lophomonadidae within the Cristamonadida, a major subdivision of Parabasalia. Unexpectedly, our phylogenetic analysis using a ribosomal RNA gene (18S, SSU) shows that L. striata is more closely related to Trichonymphida, a different group of parabasalids. This finding has several implications for research in this field. The more obvious is taxonomic. The genus Lophomonas gives the root to the family Lophomonadidae, which includes several genera (e.g. Joenia, Koruga) that do branch within the Cristamonadida. If we move Lophomonas out of Cristamonadida, we are left with a taxonomic conundrum: Lophomonas striata is no longer a Lophomonad (!). To solve this problem satisfactorily, other Lophomonas species have to be investigated in order to determine if they are still relatives of L. striata.
Other implications are about the choice of morphological characteristics that describe (and define) taxa such as Cristamonanida and Trychonympida. For example, trychonymphids have the multiple flagella originating from two or four regions, whereas Lophomonads have a single apical flagellar region, meaning that this type of organization may have arisen independently in L. striata and in the other “Lophomonads”.