Stygiella (protist)
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''Stygiella'' /ˌstɪ.d͡ʒiˈɛ.lə/ is a genus of free-living marine
flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...
s belonging to the family
Stygiellidae Stygiellidae is a family of free-living marine flagellates belonging to the order Jakobida, a deep-branching lineage within the eukaryotic supergroup Discoba. They are unicellular organisms that commonly inhabit anoxic, sulfide-rich and ammoni ...
in the
Jakobids Jakobida is an order (biology), order (sole order in the Class (biology), class Jakobea) of free-living, Heterotroph, heterotrophic, Flagellate, flagellar eukaryotes in the clade Excavata#Discoba or JEH clade, Discoba. They are small (less than 15& ...
(
excavata Excavata is an obsolete, extensive and diverse paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains ...
). The genus currently includes four species, all of which are secondary
obligate anaerobe Obligate anaerobes are microorganisms killed by normal Atmosphere of Earth, atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose vi ...
s. The species are all unicellular and crescent-shaped.Bernard, C, Simpson, A. G. B. & Patterson, D. J. (2000) Some free-living flagellates (protista) from anoxic habitats, Ophelia, 52:2, 113-142, DOI: 10.1080/00785236.1999.10409422. All members possess
hydrogenosome A hydrogenosome is a membrane-enclosed organelle found in some Anaerobic organism, anaerobic Ciliate, ciliates, Flagellate, flagellates, Fungus, fungi, and three species of Loricifera, loriciferans. Hydrogenosomes are highly variable organelles t ...
s, a type of acristate mitochondrion-derived
organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...
(MRO) that produces hydrogen gas as a metabolic product.Leger, M. M., Eme, L., Hug, L. A., & Roger, A. J. (2016). ovel hydrogenosomes in the microaerophilic jakobid ''Stygiella incarcerata'' Molecular Biology and Evolution, 33(9), 2318-2336. Retrieved April 28, 2020. doi: doi.org/10.1093/2Fmolbev/2Fmsw103. Stygiella is a deep-branching lineage within excavates, and hydrogenosome genes sometimes show eubacterium-like mechanisms that have been useful for studying of the evolutionary history of eukaryotic mitochondria.


Etymology

''Stygiella'' is a newly coined diminutive based on the name of the Greek goddess of the river
Styx In Greek mythology, Styx (; ; lit. "Shuddering"), also called the River Styx, is a goddess and one of the rivers of the Greek Underworld. Her parents were the Titans Oceanus and Tethys, and she was the wife of the Titan Pallas and the moth ...
, which in Greek mythology formed the boundary between the Earth and the Underworld.


History

The species ''Stygiella incarcerata'' was first described by Bernard et al. in 2000, sampled from Quirbray Bay, Australia and Nivå Bay, Denmark; but the species may have been previously seen by Fentel et al. in 1995 at Danish fjord.Fenchel, T., Bernard, C., Esteban, G., Finlay, B. J., Hansen, P. J., & Iversen, N. (1995). Microbial diversity and activity in a Danish fjord with anoxic deep water. Ophelia, 43(1), 45–100. The species was originally classified in the genus ''
Jakoba ''Jakoba'' is a genus in the taxon Excavata, and currently has a single described species, ''Jakoba libera'' described by David_J._Patterson, Patterson in 1990, and named in honour of Dutch botanist (Algology, Myology and Lichenology) Jakoba Rui ...
'', with the name ''Jakoba incarcerata''. Later 18S rRNA analysis by Lara et al. showed strong phylogenetic relationship between ''J. incarcerata'' and ''Andalucia godoyi'', a newly described biflagellated Jakobid from soil; the researchers therefore moved the species under the novel genus ''
Andalucia Andalusia ( , ; , ) is the southernmost autonomous community in Peninsular Spain, located in the south of the Iberian Peninsula, in southwestern Europe. It is the most populous and the second-largest autonomous community in the country. It i ...
'' in 2006.Lara, E., Chatzinotas, A., & Simpson, A. G. (2006). ''Andalucia'' (n. gen.)—the deepest branch within jakobids (jakobida; excavata), based on morphological and molecular study of a new flagellate from soil. Journal of Eukaryotic Microbiology, 53(2), 112–120. doi:10.1111/j.1550-7408.2005.00081.x. In 2015, Pánek et al. analyzed anaerobic Jakobid lineages by SSU DNA and six protein coding genes. The results indicate strong clade for all anaerobic Jakobids, forming the novel family Stygiellidae with two novel genera: ''Velundella'' and ''Stygiella''; ''A. incarcerata'' was thus classified in ''Stygiella'', along with three newly discovered species.


Habitat

All ''Stygiella'' species have been found in anoxic, sulfide- and ammonium rich sediment in the ocean bed or in brackish water. ''Stygiella'' species tolerate salinity between 19 and 56 ppt. All four species have been successfully cultured in laboratory conditions at room temperature.


Morphology

All ''Stygiella'' species have a similar morphology: they are laterally crescent-shaped or ovoidal, aloricate cells with pointed ends (''S. incarcerata''), and a diamond-shaped ventral groove covers most of the ventral side to the posterior end. There are two distinct types of body shapes present in every species: grooved cells with broadly open grooves, and swimming cells with shortened, narrower grooves. The bodies of swimming cells usually narrow from middle to the end, whereas the grooved cells are more ovoid. Reported cell lengths usually range from 6.0 to 9.0 μm The cells are biflagellated, with flagella originating close to the anterior end of the groove and extending towards the anterior and the posterior ends of the cell.Simpson, A. G., & Patterson, D. J. (2001)
On core jakobids and excavate taxa: The ultrastructure of ''Jakoba incarcerata''. Journal of Eukaryotic Microbiology
48(4), 480–492. doi:10.1111/j.1550-7408.2001.tb00183.x.
The anterior flagella are usually shorter than the body length while the posterior flagella are usually more than twice longer than the cell; the posterior flagella of ''S. incarcerata'' are generally shorter, usually about 1.5 times the cell length. The anterior flagellum of ''S. incarcerata'' has single root made of two slightly separated
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s, which originates close to the anterior
basal body A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor Wi ...
in the ventral, posterior end. The posterior flagellum has two main microtubular roots: the left one is associated with three different non-microtubular fibres as well as a composite fibre, and the right one of one type. In addition, a singlet “root” circles the posterior basal body and supports the shape of the groove. A dorsal vane attaches on the posterior flagellum, which is supported by a paraxonemal lamella that originates near the
axoneme In molecular biology, an axoneme, also called an axial filament, is the microtubule-based cytoskeletal structure that forms the core of a cilium or flagellum. Cilia and flagella are found on many cells, organisms, and microorganisms, to pr ...
. The axoneme is composed of the typical eukaryotic 9 x 2 motif. The lamella raises against the axoneme and connects to at least two axonemal doublets after approximately 100 nm apart from the axoneme. Its width gradually broadens to about 700 nm. ''Stygiella'' species mostly have a pear-shaped or sometimes a rounded nucleus close to the anterior end of the cell, with a nucleolus of 0.5 μm diameter. A single Golgi
dictyosome The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. Part of the endomembrane system in the cytoplasm, it packages proteins into membrane-bound vesicles in ...
, with generally 3 to 8
cisterna A cisterna (: cisternae) is a flattened membrane vesicle found in the endoplasmic reticulum and Golgi apparatus. Cisternae are an integral part of the packaging and modification processes of proteins occurring in the Golgi. Function Proteins begi ...
e is located immediately posterior of the basal bodies. The cytoskeleton resembles that of other excavates. The concentration of
ribosome Ribosomes () are molecular machine, macromolecular machines, found within all cell (biology), cells, that perform Translation (biology), biological protein synthesis (messenger RNA translation). Ribosomes link amino acids together in the order s ...
s is very low in the
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
. All species in ''Stygiella'' possess acristate
hydrogenosome A hydrogenosome is a membrane-enclosed organelle found in some Anaerobic organism, anaerobic Ciliate, ciliates, Flagellate, flagellates, Fungus, fungi, and three species of Loricifera, loriciferans. Hydrogenosomes are highly variable organelles t ...
s that can only perform anaerobic ATP-synthesis and lost most of its proteins for the
electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...
s. These hydrogenosomes, generally 300 to 500 nm across and 0.75 to 1 μm in length, lie close to the nucleus and often associate with major flagellar microtubular roots.


Behaviour

The cells may attach to the substrate by their flagella (mostly the anterior flagellum) or by the lateral or the dorsal cell body through a posterior cytoplasmic projection. The major morphotypes in ''S. incarcerata'' and ''S. agilis'' are swimming cells that move in a spiralling motion with only occasion adherence to substrate. Grooved morphotypes of these species attach to the substrate first by the anterior flagellum, which drags the body towards the substrate and releases when the posterior cytoplasmic projection adheres. ''S. adhaerens'' and ''S. cryptica'' are majorly grooved cells that nearly always attach to the substrate by the anterior, or seldom the posterior flagellum; few swimming cells have been observed in these species.


Metabolism

The hydrogenosomes of ''Stygiella'' seem to lack an organellar genome and the majority of the Complex I subunits for an electron transfer chain but contain proteins for eubacterium-like pyruvate decarboxylation, such as pyruvate:ferredoxin oxidoreductase and eFehydrogenase, which also exist in other anaerobic excavates of different lineages. This convergent evolution may be the result of similar lateral gene transfer. Compared to some parasitic anaerobic excavates, such as ''
Trichomonas vaginalis ''Trichomonas vaginalis'' is an Anaerobic organism, anaerobic, flagellated protozoan parasite and the causative agent of a Sexually transmitted infection, sexually transmitted disease called trichomoniasis. It is the most common pathogenic protoz ...
'', the hydrogenosomes of ''S. incarcerata'' retain more import proteins and more functional amino acid mechanism. In addition, it has an
oxidative stress Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal ...
response similar to that of other anaerobic protists. Iron-sulfur cluster assemblies are present in the hydrogenosomes, which is consistent with all other mitochondrion-derived organelles.


List of species

Four species of ''Stygiella'' are recognized: *''
Stygiella incarcerata ''Stygiella incarcerata'' is a species of Excavata. Taxonomy ''Stygiella incarcerata'' was originally described to the genus ''Jakoba'' in 2000, but was moved to the newly created genus ''Andalucia Andalusia ( , ; , ) is the southernmost ...
'' (Bernard, Simpson and Patterson 2000) Pánek, Tábosky and Čepička 2015. *'' Stygiella adhaerens'' Pánek, Táborský & Čepička 2015 *'' Stygiella cryptica'' Pánek, Táborský & Čepička 2015 *'' Stygiella agilis'' Pánek, Táborský & Čepička 2015


References

{{Taxonbar, from=Q96406627 Flagellates Anaerobes Taxa described in 2015