''Trimastix'' is a genus of excavate

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s, the sole occupant of the order Trimastigida. ''Trimastix'' are bacterivorous, free living and

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

. It was first observed in 1881 by

William Kent William Kent (c. 1685 – 12 April 1748) was an English architect, landscape architect, painter and furniture designer of the early 18th century. He began his career as a painter, and became Principal Painter in Ordinary or court painter, b ...

. There are few known species, and the genus's role in the ecosystem is largely unknown. However, it is known that they generally live in marine environments within the tissues of decaying organisms to maintain an anoxic environment.Brugerolle, G., & Patterson, D. (1997). Ultrastructure of Trimastix convexa Hollande, an amitochondriate anaerobic flagellate with a previously undescribed organization. European Journal of Protistology, 33(2), 121-130. Much interest in this group is related to its close association with other members of

Preaxostyla Anaeromonadea, also known as Preaxostyla, is a class of excavate protists, comprising the oxymonads, '' Trimastix'', and '' Paratrimastix''. This group is studied as a model system for reductive evolution of mitochondria, because it includes bo ...

. These organisms do not have classical

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

, and as such, much of the research involving these microbes is aimed at investigating the evolution of mitochondria. A freshwater

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 ...

of similar morphology used to be included in this genus as '' Trimastix pyriformis'', but was moved to ''

Paratrimastix ''Paratrimastix'' is a genus of free-living freshwater anaerobic excavate protists from the group Metamonad The metamonads are a large group of flagellate amitochondriate microscopic eukaryotes. They include the retortamonads, diplomonad ...

'' in 2015.

Taxonomy

* Order Trimastigida Cavalier-Smith 2003 ** Family Trimastigidae Saville Kent 1880 *** Genus ''Trimastix'' Saville Kent 1880 **** Species ''T. cionae'' (Parona Corrado 1886) Grassé 1952 'Elvirea cionae'' Parona Corrado 1886**** Species ''T. elaverinus'' Dumas 1930 **** Species ''T. inaequalis'' Bernard, Simpson & Patterson 2000 **** Species ''T. marina'' Kent 1880

History of knowledge

''Trimastix'' were first described by William Kent in 1881 when he observed a ''Trimastix'' cell in a sample sourced from decaying fuci seaweed. He described the genus at the time as free-swimming naked

animalcule Animalcule (; ) is an archaic term for microscopic organisms that included bacteria, protozoans, and very small animals. The word was invented by 17th-century Dutch scientist Antonie van Leeuwenhoek to refer to the microorganisms he observed i ...

s that are oval, or pear shaped, with a membranous border and three

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

inserted on the anterior end. Kent observed one flagellum facing forwards and two facing backwards.Kent, W. S. (1881). A manual of the infusoria: including a description of all known flagellate, ciliate, and tentaculiferous protozoa, British and foreign, and an account of the organization and affinities of the sponges (Vol. 1). David Bogue, London, England. It was also noted in this account that ''Trimastix'' had a visually apparent

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

and

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists, including unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contrac ...

but no visual oral aperture. Kent determined that ''Trimastix'' was a distinct genus, despite similarities to ''Dallingeria'', because of the lateral border he observed which was not present in ''Dallingeria''. It was later determined that the lateral border Kent was referring to was in fact the oral aperture of ''Trimastix'', which also contained a fourth flagella. Today, the morphology of ''Trimastix'' is better understood, including details not initially observed by Kent, such as ''Trimastix'' lacking a conventional mitochondrion. Current research indicates that despite there being no evidence that the organelle can produce ATP, there are certain mitochondrial functions that it appears to have maintained.

Habitat and ecology

''Trimastix'' can only survive in anaerobic habitats, but unlike many anaerobes without typical mitochondria, ''Trimastix'' are not parasitic. ''Trimastix'' instead consume

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

through their ventral groove. In order to maintain an anoxic environment without parasitism or endosymbiosis, ''Trimastix'' are most often found inside the tissues of dead and decaying marine vegetation.

Morphology and ultrastructure

''Trimastix'' cells are oblong broad anteriorly and taper posteriorly. ''Trimastix'' is 20 μm long and 8 μm wide. A kinetid of four

is located on the anterior end of the cell with one flagella anteriorly oriented, two flagella posteriorly oriented, and the fourth flagella sitting within an oral groove on the ventral side. ''Trimastix'' have one anterior pear-shaped

that contains a large

nucleolus The nucleolus (; : nucleoli ) is the largest structure in the cell nucleus, nucleus of eukaryote, eukaryotic cell (biology), cells. It is best known as the site of ribosome biogenesis. The nucleolus also participates in the formation of signa ...

. ''Trimastix'' species do not have typical aerobic mitochondria, but they do have remnants of an ancestral

mitochondrion A mitochondrion () is an organelle found in the cell (biology), cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosine tri ...

, in the form of a

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 ...

- or

mitosome A mitosome (also called a ''crypton'' in early literature) is a mitochondrion-related organelle (MRO) found in a variety of parasitic unicellular eukaryotes, such as members of the supergroup Excavata. The mitosome was first discovered in 1999 in ...

-like organelle. There is no evidence this organelle produces ATP. The organelle still appears to be targeted by proteins involved in

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

metabolism, transport and maturation of proteins, and transport of metabolites so it likely retains some mitochondrial function relating to those areas.

References

{{Taxonbar, from=Q622727 Metamonads Metamonad genera Anaerobes Microorganisms