Trypanosomatida is a group of

kinetoplastid Kinetoplastida (or Kinetoplastea, as a class) is a group of flagellated protists belonging to the phylum Euglenozoa, and characterised by the presence of a distinctive organelle called the kinetoplast (hence the name), a granule containing a lar ...

unicellular organism A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

s distinguished by having only a single

flagellum 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 ...

. The name is derived from the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of some trypanosomatid species. All members are exclusively

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

, found primarily in

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. A few genera have life-cycles involving a secondary host, which may be a

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

. These include several species that cause major diseases in humans. Some trypanosomatida are

intracellular parasite Intracellular parasites are microparasites that are capable of growing and reproducing inside the cells of a host. They are also called intracellular pathogens. Types There are two main types of intracellular parasites: Facultative and Obligate ...

s, with the important exception of ''

Trypanosoma brucei ''Trypanosoma brucei'' is a species of parasitic Kinetoplastida, kinetoplastid belonging to the genus ''Trypanosoma'' that is present in sub-Saharan Africa. Unlike other protozoan parasites that normally infect blood and tissue cells, it is excl ...

''.

Medical importance

The three major

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

diseases caused by trypanosomatids are; African

trypanosomiasis Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other disea ...

(

sleeping sickness African trypanosomiasis is an insect-borne parasitic infection of humans and other animals. Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species '' Trypanosoma b ...

, caused by ''

'' and transmitted by

tsetse flies Tsetse ( , or ) (sometimes spelled tzetze; also known as tik-tik flies) are large, biting flies that inhabit much of tropical Africa. Tsetse flies include all the species in the genus ''Glossina'', which are placed in their own family, Glos ...

), South American trypanosomiasis (

Chagas disease Chagas disease, also known as American trypanosomiasis, is a tropical parasitic disease caused by ''Trypanosoma cruzi''. It is spread mostly by insects in the subfamily Triatominae, known as "kissing bugs". The symptoms change throughout the ...

, caused by '' T. cruzi'' and transmitted by triatomine bugs), and

leishmaniasis Leishmaniasis is a wide array of clinical manifestations caused by protozoal parasites of the Trypanosomatida genus ''Leishmania''. It is generally spread through the bite of Phlebotominae, phlebotomine Sandfly, sandflies, ''Phlebotomus'' an ...

(a set of trypanosomal diseases caused by various species of ''

Leishmania ''Leishmania'' () is a genus of parasitic protozoans, single-celled eukaryotic organisms of the trypanosomatid group that are responsible for the disease leishmaniasis. The parasites are transmitted by sandflies of the genus '' Phlebotomus'' ...

'' transmitted by

sandflies Sandfly or sand fly is a colloquial name for any species or genus of flying, biting, blood-sucking dipteran (fly) encountered in sandy areas. In the United States, ''sandfly'' may refer to certain horse flies that are also known as "greenhead ...

: : :This review cites this research. : : ).

Evolution

The family is known from fossils of the extinct genus ''

Paleoleishmania ''Paleoleishmania'' is an extinct genus of kinetoplastids, a monophyletic group of unicellular parasitic flagellate protozoa. At present it is placed in the family Trypanosomatidae. The genus contains two species, the type species ''Paleoleishm ...

'' preserved in Burmese

amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

dating to the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

(100 mya) and

Dominican amber Dominican amber is amber from the Dominican Republic derived from resin of the extinct tree '' Hymenaea protera''. Dominican amber differentiates itself from Baltic amber by being nearly always transparent, and it has a higher number of fossil in ...

from the

Burdigalian The Burdigalian is, in the geologic timescale, an age (geology), age or stage (stratigraphy), stage in the early Miocene. It spans the time between 20.43 ± 0.05 annum, Ma and 15.97 ± 0.05 Ma (million years ago). Preceded by the Aquitanian (sta ...

(20–15 mya) of

Hispaniola Hispaniola (, also ) is an island between Geography of Cuba, Cuba and Geography of Puerto Rico, Puerto Rico in the Greater Antilles of the Caribbean. Hispaniola is the most populous island in the West Indies, and the second-largest by List of C ...

. The genus ''

Trypanosoma ''Trypanosoma'' is a genus of kinetoplastids (class Trypanosomatidae), a monophyletic group of unicellular parasitic flagellate protozoa. Trypanosoma is part of the phylum Euglenozoa. The name is derived from the Ancient Greek ''trypano-'' (b ...

'' is also represented in Dominican amber in the extinct species '' T. antiquus''.

Taxonomy

Three genera are dixenous (two hosts in the life cycle) – ''

'', '' Phytomonas'' and ''

'', while The remainder are monoxenous (one host in the life cycle). '' Paratrypanosoma'' appears to be the first evolving branch in this order. Fifteen genera are recognised in the ''Trypanosomatidae'' and there are three subfamilies – '' Blechomonadinae'', '' Leishmaniinae'' and ''

Strigomonadinae Strigomonadinae is a subfamily of protists in the order Trypanosomatida. All species in this taxon harbor endodymbiontic bacteria of the '' Candidatus Kinetoplastibacterium'' genus. Use as model organisms Several species of the Strigomonadinae, ...

''. The genera in the subfamily ''

'' are characterised by the presence of obligatory intracellular bacteria of the Kinetoplastibacterium genus. * Family Trypanosomatidae Calkins 1926 rypanomorphidae Woodcock 1906; Trypanosomataceae Senn 1911** Genus '' Agamomonas'' Grassé 1952 ** Genus '' Batracoleishmania'' Dasgupta 2011 ** Genus '' Blastocrithidia'' Laird 1959 ** Genus '' Cercoplasma'' Roubaud 1911 ** Genus '' Cystotrypanosoma'' Roubaud 1911 ** Genus ''

Jaenimonas ''Jaenimonas'' is a genus of trypanosomatid parasite that infects mushroom-feeding ''Drosophila'', similar to '' Crithidia'' parasites of Bumblebees. '' Jaenimonas drosophilae'' is the sole representative of this genus. The genus is named in hon ...

'' Votypka & Hamilton 2015 ** Genus '' Lamellasoma'' Davis 1947 ** Genus '' Leptowallaceina'' Podlipaev & Frolov 2000 ** Genus '' Lewisonella'' Chalmers 1918 nomen dubium ** Genus '' Malacozoomonas'' Nicoli, Penaud & Timon-David 1972 ** Genus '' Nematodomonas'' Nicoli, Penaud & Timon-David 1972 ** Genus †''

'' Poinar & Poinar, 2004 ** Genus †'' Paleotrypanosoma'' Poinar 2008 ** Genus '' Paramecioides'' Grassé 1882 ** Genus '' Sauroleishmania'' Ranque 1973 ** Genus '' Sergeia'' Svobodová et al. 2007 non Stimpson 1860 non Nasonov 1923 non Sergio Manning & Lemaitre 1994 ** Genus '' Trypanomonas'' Danilewsky 1885 ** Genus '' Trypanomorpha'' Woodcock 1906 ** Genus '' Undulina'' Lankester 187 ** Genus '' Wallaceina'' Bulat, Mokrousov & Podlipaev 1999 'Proteomonas'' Podlipaev, Frolov & Kolesnikov 1990 non Hill & Wetherbee 1986">Proteomonas.html" ;"title="'Proteomonas">'Proteomonas'' Podlipaev, Frolov & Kolesnikov 1990 non Hill & Wetherbee 1986** Genus ''Wallacemonas'' Kostygov & Yurchenko 2014 ** Subfamily Paratrypanosomatinae Votýpka & Lukeš 2013 *** Genus '' Paratrypanosoma'' Votypka & Lukes 2013 ** Subfamily Trypanosomatinae ::* Genus ''

'' Gruby 1843 :* Subfamily Blechomonadinae Votypka & Suková 2013 ::* Genus '' Blechomonas'' Votypka & Suková 2013 Leishmania donovani 01

:* Subfamily Leishmaniinae sensu Maslov & Lukeš 2012 ::* Clade Crithidiatae Maslov & Lukeš 2012 CRITHIDIA 2

:::* Genus ''

Crithidia ''Crithidia'' is a genus of trypanosomatid Euglenozoa. They are parasites that exclusively parasitise arthropods, mainly insects. They pass from host to host as cysts in infective faeces and typically, the parasites develop in the digestive trac ...

'' Léger 1902 :::* Genus '' Leptomonas'' Kent 1880 :::* Genus '' Lotmaria'' Schwarz 2015 ::* Clade Leishmaniatae Maslov & Lukeš 2012 :::* Genus '' Borovskyia'' Kostygov & Yurchenko 2017 :::* Genus '' Endotrypanum'' Mesnil & Brimont 1908 :::* Genus ''

'' Ross 1903 :::* Genus '' Novymonas'' Votýpka et al. 2015 :::* Genus '' Paraleishmania'' Cupolillo et al. 2000 :::* Genus '' Zelonia'' Shaw, Camargo et Teixeira 2016 :* Subfamily Phytomonadinae Kostygov & Yurchenko 2015 ::* Genus '' Herpetomonas'' Kent 1880 non Donovan 1909 ::* Genus '' Lafontella'' Kostygov & Yurchenko 2015 Epifluorescence microscopy of Phytomonas serpens

Epifluorescence microscopy of Phytomonas serpens

::* Genus '' Phytomonas'' Donovan 1909 :* Subfamily

Votypka et al. 2014 ::* Genus '' Angomonas'' Souza & Corte-Real 1991 ::* Genus '' Kentomonas'' Votypka et al. 2014 ::* Genus '' Strigomonas'' Lwoff & Lwoff 1931

Life cycle

Some trypanosomatids only occupy a single

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

, while many others are

heteroxenous Heteroxeny, or heteroxenous development, characterizes a parasite whose development involves several host species. Heteroxeny has been used as the basis for splitting genera. When there are two or three hosts, the development cycle is named d ...

: they live in more than one host species over their life cycle. This heteroxenous life cycle typically includes the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

of a bloodsucking

and the blood and/or tissues of a

. Rarer hosts include other bloodsucking invertebrates, such as

leech Leeches are segmented parasitism, parasitic or Predation, predatory worms that comprise the Class (biology), subclass Hirudinea within the phylum Annelida. They are closely related to the Oligochaeta, oligochaetes, which include the earthwor ...

es, and other organisms such as

s. Different species go through a range of different morphologies at different stages of the life cycle, with most having at least two different morphologies. Typically the promastigote and epimastigote forms are found in insect hosts, trypomastigote forms in the mammalian

bloodstream In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart an ...

and amastigotes in

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

environments. Among commonly studied examples, '' T. brucei'', '' T. congolense'', and '' T. vivax'' are extracellular, while '' T. cruzi'' and ''

'' spp. are intracellular. Trypanosomatids with intracellular stages express proteins on their surfaces. de Paiva ''et al.'', 2015 illuminates δ-amastins' roles in intracellular success.

Sexual reproduction

Trypanosomatids that cause globally known diseases such

(''

'' species),

African trypanosomiasis African trypanosomiasis is an insect-borne parasitic infection of humans and other animals. Human African trypanosomiasis (HAT), also known as African sleeping sickness or simply sleeping sickness, is caused by the species ''Trypanosoma bru ...

referred to as sleeping sickness (''

''), and

(''

Trypanosoma cruzi ''Trypanosoma cruzi'' is a species of parasitic euglenoids. Among the protozoa, the trypanosomes characteristically bore tissue in another organism and feed on blood (primarily) and also lymph. This behaviour causes disease or the likelihood ...

'') were found to be capable of

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

and genetic exchange. These findings indicate the capability for

sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...

in the Trypanosomatida.

Morphologies

A variety of different morphological forms appear in the life cycles of trypanosomatids, distinguished mainly by the position, length and the cell body attachment of the

. The

kinetoplast A kinetoplast is a network of circular DNA (called kDNA) inside a mitochondrion that contains many copies of the mitochondrial genome. The most common kinetoplast structure is a disk, but they have been observed in other arrangements. Kinetoplasts ...

is found closely associated with the

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 ...

at the base of the flagellum and all species of trypanosomatid have a single nucleus. Most of these morphologies can be found as a life cycle stage in all trypanosomatid genera however certain morphologies are particularly common in a particular genus. The various morphologies were originally named from the genus where the morphology was commonly found, although this terminology is now rarely used because of potential confusion between morphologies and genus. Modern terminology is derived from the Greek; "mastig", meaning whip (referring to the flagellum), and a prefix which indicates the location of the flagellum on the cell. For example, the amastigote (prefix "a-", meaning no flagellum) form is also known as the leishmanial form as all ''

'' have an amastigote life cycle stage. *

Amastigote An amastigote is a protist cell that does not have visible external flagella or cilia. The term is used mainly to describe an intracellular phase in the life-cycle of trypanosomes that replicates. It is also called the leishmanial stage, since in ...

(leishmanial). Amastigotes are a common morphology during an intracellular lifecycle stage in a mammalian host. All ''

'' have an amastigote stage of the lifecycle. ''Leishmania'' amastigotes are particularly small and are among the smallest eukaryotic cells. The flagellum is very short, projecting only slightly beyond the flagellar pocket. * (leptomonad). The promastigote form is a common morphology in the insect host. The flagellum is found anterior of nucleus emerging directly from the anterior cell body. The kinetoplast is located in front of the nucleus, near the anterior end of the body. * (crithidial). Epimastigotes are a common form in the insect host and ''

'' and '' Blastocrithidia'', both parasites of insects, exhibit this form during their life cycles. The flagellum exits the cell anterior of nucleus and is connected to the cell body for part of its length by an undulating membrane. The kinetoplast is located between the nucleus and the anterior end. * (trypanosomal). This stage is characteristic of the genus ''

'' in the mammalian host bloodstream as well as infective metacyclic stages in the fly vector. In trypomastigotes the

is near the posterior end of the body, and the flagellum lies attached to the cell body for most of its length by an undulating membrane. * (herpetomonad). A rarer morphology where the flagellum posterior of nucleus, passing through a long groove in the cell. * . A morphotype where the flagellum does not extend beyond the deep flagellar pocket. Image:LeishmaniaMexicana Amastigote SEM.jpg, Amastigote: False colour SEM micrograph of

amastigote An amastigote is a protist cell that does not have visible external flagella or cilia. The term is used mainly to describe an intracellular phase in the life-cycle of trypanosomes that replicates. It is also called the leishmanial stage, since in ...

form ''

Leishmania mexicana ''Leishmania mexicana'' is a species of obligate intracellular parasites of the protozoan genus ''Leishmania''. In Mexico and Central America, this parasite is the primary cause of cutaneous leishmaniasis. It is also endemic to Texas, where 69 ...

''. The cell body is shown in orange and the flagellum is in red. 219 pixels/μm. Image:LeishmaniaMexicana Promastigote SEM.jpg, Promastigote: False colour SEM micrograph of promastigote form ''

''. The cell body is shown in orange and the flagellum is in red. 119 pixels/μm. Image:TrypanosomaBrucei_ProcyclicTrypomastigote_SEM.jpg, Trypomastigote: False colour SEM micrograph of procyclic form ''

''. The cell body is shown in orange and the flagellum is in red. 84 pixels/μm.

Other features

Notable characteristics of trypanosomatids are the ability to perform

trans-splicing ''Trans''-splicing is a special form of RNA processing where exons from two different primary RNA transcripts are joined end to end and ligated. It is usually found in eukaryotes and mediated by the spliceosome, although some bacteria and archa ...

of RNA and possession of

glycosome The glycosome is a membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes ...

s, where much of their

glycolysis Glycolysis is the metabolic pathway that converts glucose () into pyruvic acid, pyruvate and, in most organisms, occurs in the liquid part of cells (the cytosol). The Thermodynamic free energy, free energy released in this process is used to form ...

is confined to. The

acidocalcisome Acidocalcisomes are rounded electron-dense acidic organelles, rich in calcium and polyphosphate and between 100 nm and 200 nm in diameter. Acidocalcisomes were originally discovered in Trypanosoma, Trypanosomes (the causing agents of Afri ...

, another

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 ...

, was first identified in trypanosomes.

Bacterial endosymbiont

Six species of trypanosomatids are known to carry an additional proteobacterial

endosymbiont An endosymbiont or endobiont is an organism that lives within the body or cells of another organism. Typically the two organisms are in a mutualism (biology), mutualistic relationship. Examples are nitrogen-fixing bacteria (called rhizobia), whi ...

, termed TPE (trypanosomatid proteobacterial endosymbionts). These trypansomatids ('' Strigomonas oncopelti'', '' S. culicis'', '' S. galati'', '' Angomonas desouzai'', and '' A. deanei'') are in turn known as SHTs, for symbiont-harboring trypanosomatids. All such symbionts have a shared evolutionary origin and are classified in the

Candidatus In prokaryote nomenclature, ''Candidatus'' (abbreviated ''Ca.''; Latin for "candidate of Roman office") is used to name prokaryotic taxa that are well characterized but yet- uncultured. Contemporary sequencing approaches, such as 16S ribosomal R ...

genus "Kinetoplastibacterium". As with many symbionts, the bacteria have a much reduced genome compared to their free-living relatives of genera '' Taylorella'' and '' Achromobacter''. (

GTDB The Genome Taxonomy Database (GTDB) is an online database that maintains information on a proposed nomenclature of prokaryotes, following a phylogenomic approach based on a set of conserved single-copy proteins. In addition to resolving paraphyl ...

finds the genus sister to '' Proftella'', a symbiont of '' Diaphorina citri''.) Reflecting their inability to live alone, they have lost genes dedicated to essential biological functions, relying on the host instead. They have modified their division to become synchronized with the host. In ''S. culicis'' at least, the TPE helps the host by synthesizing

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

and producing essential enzymes, staying tethered to the

References

* * * * * * * * * * * * * *
online
. A comprehensive survey of the organisms' natural history.