Retortamonas is a genus of flagellated excavates. It is one of only two genera belonging to the family Retortamonadidae along with the genus Chilomastix. The genus parasitizes a large range of hosts including humans. Species within this genus are considered harmless commensals which reside in the intestine of their host. The wide host diversity is a useful factor given that species are distinguished based on their host rather than morphology. This is because all species share similar morphology, which would present challenges when trying to make classifications based on structural anatomy. Although Retortamonas currently includes over 25 known species, it is possible that some defined species are synonymous, given that such overlapping species have been discovered in the past. Further efforts into learning about this genus must be done such as cross-transmission testing as well as biochemical and genetic studies. One of the most well-known species within this genus is Retortamonas intestinalis, a human parasite that lives in the large intestine of humans.
Etymology
Retort- is derived from the Latin re-torqueo – “to twist back” while the Greek term monas- “one unit, single” refers to its singularity. During locomotion the anterior region of the body twists in a clock-wise direction about its axis, propelling the cell to swim forward, and therefore, the body structure often appears twisted.
History of knowledge
First discovery of the genus
The human parasite Retortamonas intestinalis was first discovered in 1917 Egypt by Wenyon and O’Connor. This case was reported by a soldier who was diagnosed to be infected with Waskia intestinalis, a species which was later renamed Embadomonas intestinalis by Chalmers and Pekkola in 1918. Afterwards, both Waskia and Embadomonas species were both revised to Retortamonas by Wenrich in 1932.
Modern research
In more recent findings, a study on the presence of parasites in the intestinal contents of ostriches conducted by a team in Spain 2001 discovered that this genus infected these birds. This was the first time in history that Retortamonas was found to be a parasite of the taxon Aves. There is a chance that the Retortamonas species discovered by this team is one that has already been identified in other hosts, and that other species of birds are also infected.
In previous studies, it was determined that Retortamonas species infect a wide range of hosts including mammals, amphibians, reptiles and insects. Since species are classified on host-type, rather than morphology, this gave rise to many species within this genus. This knowledge of the genus parasitizing a wide range of hosts was used by a team in Asia in 2018 as a tool to assess the phylogeny of Retortamonas species and determine if overlap of synonymous species exists. Through comparison of Retortamonas haplotypes of ribosomal RNA subunits and network analysis between mammal-, amphibian-, and insect-infecting species, a discovery about the species was made by the research team. Results showed that while haplotypes from vertebrate-infecting species formed a three-cluster formation, the insect species were separated, in an isolated cluster with Chilomastix. This indicated insect-infecting species are in fact closer-related to Chilomastix than they are to other Retortamonas. In addition, it was found that Retortamonas infecting humans (R. intestinalis) and other mammals are most likely the same species, and transfer between mammalian hosts likely occurs through zoonotic transmission. Strong evidence showcased this through all mammalian-infecting species grouping together in one monophyphyletic cluster. This discovery is a major piece of evidence towards promoting the reassessment of the current Retortamonas phylogeny. In addition, it addresses the issue that synonymous species are most likely present. It is possible that the three clusters recognized by the team is a telling piece of evidence that only three species of Retortamonas exists.