Kentomonas sorsogonicus Votypka et Lukes 2014

A strangely named organism, one of those I like to choose for the morbid fascination of illustrating the unknown. Kentomonas sorsogonicus isn't in AlgaeBase, so I based its taxonomy on that of NCBI Taxonomy.

The organism belongs to the subfamily Strigomonadinae, family Trypanosomatidae, order Trypanosomatida. That alone is enough to tell you that Kentomonas is related to the legendary Trypanosoma (sleeping sickness) and Leishmania. In this order, no one is spared: all its members are parasites. Trypanosomatids have several characteristics, among which I can highlight the kinetoplast (an organelle with a dense granule of kDNA located within the mitochondria, and usually associated with the basal bodies of the flagella), and the presence of glycosomes, which store glycolytic enzymes for glycolysis (Michels et al. 2006).

The order Trypanosomatida is included in the subclass Metakinetoplastina, along with the other orders Eubodonida, Neobodonida, and Parabodonida. These other orders are very diverse in their organisms, a few being parasitic and most free-living. In fact, I illustrated a species of Neobodonida, Klosteria bodomorphis, some time ago.

The subclass Metakinetoplastina is included in the class Kinetoplastea, and this in the phylum Euglenozoa, which makes Kentomonas distantly related to more "innocent" organisms like Euglena or Diplonema. Euglenozoa is included in the clade Discoba (which includes the other phyla Heterolobosea, Jakobea (which includes the last species I illustrated, Andalucia godoyi), and Tsukubea), and finally in the domain Eukaryota.

Anyway, the main source that I have used to create the illustrations, and the information written here, was "Kentomonas gen. n., a New Genus of Endosymbiont-containing Trypanosomatids of Strigomonadinae subfam. n." (2014), by Jan Votýpka, Alexei Yu Kostygov, Natalya Kraeva, Anastasiia Grybchuk-Ieremenko, Martina Tesařová, Danyil Grybchuk, Julius Lukeš and Vyacheslav Yurchenko. Protist, Vol. 165, Issue 6. 825-838 pp.

Another source was: "Farming, slaving and enslavement: histories of endosymbioses during kinetoplastid evolution", (2018), by Jane Harmer, Vyacheslav Yurchenko, Anna Nenarokova, Julius Lukeš and Michael L. Gingerby. Parasitology, 145, 1311–1323. https://doi.org/10.1017/S0031182018000781 

A peaceful screamer reminder: the following illustrations are free to use and are also available on Wikimedia Commons. Of course, commercial use of these images is not permitted, nor is their use without proper attribution. "DOTkamina (2026)" is sufficient.

Kentomonas sorsogonicus was found infecting the hindgut of a female Sarcophaga fly (species undetermined), which was captured near Donsol, Sorsogon, in the Philippines. Its cellular form is called a "choanomastigote": an oval or rounded shape with a ring-like structure at its anterior end from which the flagellum protrudes. I have indicated this ring in the illustration. In Kentomonas sorsogonicus, the choanomastigote is more elongated, giving it a "barleycorn" appearance. You, as a likely native English speaker, will know what a "barleycorn" is because either I'm searching incorrectly, or I'm getting seeds I've never seen before.

Another unsettling thing is that the "choanomastigote" has the kinetoplast anterior to the nucleus (watch this image). I thought I'd messed up because I depicted the kinetoplast posterior to the nucleus in my illustration, near the basal body. However, in K. sorsogonicus, the kinetoplast doesn't appear to be fixed; its position varies depending on the individual, being posterior, anterior, or lateral to the nucleus, or wherever you like. But that's perfect for me because I didn't have to correct anything, haha.

Speaking of the flagellar pocket, it seems to be incredibly long and occupy a large part of the cell, as can be seen in Votýpka et al. (2014): Figure 2B, reaching the area where the nucleus and the endosymbiont are located (in the posterior region). Logically, "beneath" the flagellar pocket (which, remember, is an invagination that envelops the flagellar axoneme) is the basal body, whose size I don't know, so I've represented it with a "normal" size for me, but it's up to you to judge.

Flagellar axoneme

The axoneme is 9+2, the standard microtubular structure of eukaryotic flagella (9 peripheral microtubular doublets surrounding two central microtubular singlets). This axoneme, when enveloped by the plasma membrane, is what is called the "flagellum." Since the flagellar pocket is an invagination, its interior is technically lined by the plasma membrane. The flagellum, therefore, originates from inside the cell, emerges through the ring, and widens as it does so. The flagellum has a paraflagellar rod, a protein structure that supports the flagellum. In other trypanosomatids, this rod is well-developed, but in K. sorsogonicus and other species of the subfamily Strigomonadinae, it is inconspicuous (rudimentary or almost nonexistent). I have depicted the paraflagellar rod along a section of the first part of the flagellum as it emerges from the ring. I don't know if it will be a fragmented structure, if it's shorter, or if it occupies the entire flagellum.

The flagellar pocket is an invagination shaped like a round-bottomed bottle with a neck (like a Florence flask). This means that near the anterior part of the cell, where it opens with the ring, it's narrower, and the plasma membrane that acts as its inner "wall" is closer to the plasma membrane that surrounds the axoneme (that is, the flagellum). It's in this area of ​​contact that we find the desmosomes, two or three rows of them that attach the flagellum to the membrane of the flagellar pocket.

K. sorsogonicus, cell anatomy

Transversal section of the flagellar pocket in the anterior zone, with the desmosomes.

The organism has an oval-shaped nucleus, which, according to Votýpka et al. (2014): Figure 2B, appears to be located at the posterior of the cell, with the endosymbiont even further posterior. This endosymbiont is a β-proteobacterium, known as Candidatus Kinetoplastibacterium sorsogonicusi Yurchenko et Kostygov sp. n. This symbiont is typically surrounded by glycosomes, which is why I have depicted them in greater numbers around the symbiont.

The kinetoplast is cylindrical and has a loose network of kDNA fibrils. The kinetoplast is located within the mitochondrion, which, as in other species, is single and reticulated. In K. sorsogonicus, the mitochondrion is so reticulated that it extends close to the plasma membrane, pushing it outward like longitudinal horizontal varices, forming the longitudinal ridges visible on the cell's exterior. The mitochondria are rich in tubular cristae.

SEM external appearance.

The endoplasmic reticulum appears to be a structure as branched as the mitochondria, distributed throughout the cell, or at least that's what has been observed in other trypanosomatids (Sandes and Queiroz de Figueiredo 2022). In the case of K. sorsogonicus, its actual appearance is not described; I have depicted it as much less extended, almost near the nucleus. This shape and size are speculative, and it could actually be more widespread throughout the cell. The shape of the Golgi apparatus is also speculative.

In addition to the main image, I have also drawn the organism's external appearance as it would be seen under a scanning electron microscope (SEM), where the ring and, above all, the mitochondrial ridges are visible. I have also drawn the cross-section of the flagellum's axoneme with the paraflagellar rod; the cross-section of the anterior region of the cell where the flagellar pocket is narrow and in contact with the flagellum via desmosomes (in the main image, I have depicted two rows of desmosomes that are not very noticeable; in the cross-section, the desmosomes are more visible, but only one row is shown); and the cross-section of a posterior region of the cell, where the nucleus, the posteriorly widened portion of the flagellar pocket, the flagellum's axoneme within the flagellar pocket, and the mitochondrion are visible. In the cross-section, the mitochondrion appear as a cluster of individual, round mitochondria. I hope I have pointed out the branches near the surface that form the ridges, giving, in this cross-section, a wavy cell surface.

And now...

some non-labeled icons

That's all I had to say about this organism.