Rosculus

Rosculus
Scientific classification
Domain:	Eukaryota
(unranked):	SAR
(unranked):	Rhizaria
Phylum:	Cercozoa
Class:	Helkesea
Order:	Helkesida
Family:	Sainouroidea
Genus:	Rosculus Hawes, 1963
Species
R. eleongata Jousset, Bass & Geisen 2016 R. ithacus Hawes 1963 R. macrobrachii (Aravindan, Kalavati & Sheeja 2002) R. terrestris Jousset, Bass & Geisen 2016 R. tropidonoti Kalavati & Lakshminarayana 1982

Rosculus is a genus of parasitic organisms which are poorly studied. Taxonomically, Rosculus is currently accepted to be in the family Sainouroidea, which contains a sister genus and Rosculus. Many species in this genus are aquatic, but genomic data shows that some species are terrestrial. Rosculus is thought to thrive in anaerobic and aerobic environments. This protist if very small in size, and it contains a massive genome. One defining characteristic of Rosculus is its discoidal cristae but morphologically.

Taxonomy

Rosculus is a genus of organisms in the supergroup Rhizaria. Under Rhizaria, we see a group of cercozoan flagellates, called Sainouroidea, which contains two genera of amoebae: Rosculus and its sister group, Guttulinopsis. These two groups are distinguished because Guttulinopsis displays aggregate multicellularity, and they can have a fruiting body stage, and Rosculus does not. Other than the fruiting structures and aggregate multicellularity, there is little to no morphological difference between these sister taxa. 18S rDNA must be sequenced in many cases to differentiate species in the genus Rosculus vs. Guttulinopsis. Using 18S V4 amplicons, researchers were able to place Rosculus as a Cercozoan flagellate to begin with. Little research has been published on Sainouroideans, however, data suggests that this group is very genetically remarkably diverse. Current publications suggest that Sainoiroidea contain five genera: Cholamonas, Sainouron, Helkesimastix, Guttulinopsis, and Rosculus. Rosculus is not a well-studied genus in protistology. Like many protists, Rosculus has a limited quantity of published, up to date information. The taxonomic information published changes frequently and published scientific papers should be scouted recently for the most up to date information. Currently, Rosculus also contains a handful of published species.

Genomic information

Several published Rosculus species include R. ithacus, R. elongate, and R. terrestris. One Rosculus species, R. vilicus is reported to have a massive mitochondrial genome, made up of about 185,000 bp. For reference, human mitochondrial genomes only contain 16,569 bp. Rosculus’s nuclear genome contains 41 billion bp. This is again exceptionally large in comparison to the human genome, which contains about 3 billion bp. This is an incredible amount of genetic information packed into a microscopic organism.  

Size and locomotion

Rosculus is tiny in size. This genus contains organisms that range from 2-13 micrometers in length. What is more interesting is the locomotion of Rosculus. When these species are on the move, they often range from 4.2 to 5.5 micrometers in diameter. These organisms have an interesting movement style. Organisms in this group move very rapidly or abruptly. They use one long hyaline pseudopod to traverse their environments. One paper suggests that the movement of Rosculus is rippling or wave-like. When looking closely at Rosculus scientists have also observed a cyst formation as well, which is a sort of dormant reproductive stage where we do not see this movement.

Living environment and parasitism

Rosculus are often found in freshwater environments. This genus thrives between 20-25ºC. Often, Rosculus are parasitic, and they can live in fish feces. Although Rosculus is often associated with aquatic environments, Rosculus was first discovered in the European grass snake’s feces. Rosculus is especially successful living in feces because animal excrements are very nutrient rich. These environments, however, are anaerobic, which indicates that Rosculus does not need a large amount of oxygen to thrive. On the other hand, Rosculus can also live in other environments. Rosculus has been found in agricultural environments such as soil, which is typically richer in oxygen than digestive tracts, and elephant dung. Since most Rosculus species are found in feces, it is very possible that soil which contains Rosculus is well fertilized. Rosculus is likely amphicozoic. That means that this genus is a free-living parasitic organism. It does not depend on its host for survival. Rosculus is only known to parasitize animal hosts. One (albeit older source claims that Rosculus has been found in human throats and on maize. One issue with poorly studied organisms is that there is a fair bit of information that may not be accurate anymore as our taxonomic understanding shifts. While Rosculus is a known parasite, it is also a beast of a predator. This organism only needs to eat bacteria to survive, and in fecal material, they have no lack of bacterial resources.

Other morphological traits

One defining trait for Rosculus is seen in their mitochondrial cristae. These cristae are mitochondrial folds. They are necessary for respiration in aerobic organisms, which is interesting, noting a previous statement that most of Rosculus is aerobic, however, some members of this group are anaerobic. These naked amoebae have discoidal instead of tubulo-vescular cristae. Furthermore, Rosculus has a spotted or sandy-like granuloplasm. A  granuloplasm is a textured location in the cytoplasm which consists of various organelles and assists in carrying out cellular functions.