''Strigomonas culicis'' is a protist and member of flagellated trypanosomatids. It is an obligate parasite in the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

of mosquito, and is in turn a

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 * ...

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

bacteria. It maintains strict mutualistic relationship with the bacteria as a sort of cell organelle (

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 ...

) so that it cannot lead an independent life without the bacteria. Along with '' Angomonas deanei'', ''S. culicis'' is researched as model organism for the evolution of symbiotic relationsships with intracellular bacteria.

Taxonomy

''S. culicis'' was first described as ''Trypanosoma'' (''Herpetomonas'') ''culicis'' in 1907 by Frederick G. Novy, Ward J. MacNeal, and Harry N. Torreyin 1907. The species name refers to the mosquito genus '' Culex'' in which it was found, although it has been found to also be present in other mosquitos such as ''

Aedes ''Aedes'' (also known as the tiger mosquito) is a genus of mosquitoes originally found in tropical and subtropical zones, but now found on all continents except Antarctica. Some species have been spread by human activity: ''Aedes albopictus'', ...

''. Another description by F.G. Wallace and A. Johnson as ''Blastocrithidia culicis'', published in 1961 based on specimens from '' Aedes vexans'', was later considered synonymous to ''Herpetomonas culicis''. Eventually, by microbiological analysis of endosymbiont harboring

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 ...

, this species was assigned to the genus '' Strigomonas'' in 2011, bearing the current name ''S. culicis''. The

obligate {{wiktionary, obligate As an adjective, obligate means "by necessity" (antonym '' facultative'') and is used mainly in biology in phrases such as: * Obligate aerobe, an organism that cannot survive without oxygen * Obligate anaerobe, an organism ...

bacterium belongs a group of ß-proteobacterium and provides nutrients to the host, in addition to influencing some of the cellular functions.

Biology

''S. culicis'' spends its life cycle in mosquitos. It migrates from the mosquito midgut and enter the body cavity ( haemocoel) and finally reside in the

salivary glands The salivary glands in many vertebrates including mammals are exocrine glands that produce saliva through a system of Duct (anatomy), ducts. Humans have three paired major salivary glands (Parotid gland, parotid, Submandibular gland, submandibula ...

. Unlike other trypanosomatids, ''S. culicis'' does not produce some amino acids such as methionine, histidine, and arginine; and vitamins such as thiamin, nicotinamide, and riboflavin. The bacterium provides these nutrients. In addition, it also provides enzymes required by the host for amino acid synthesis,

lipid Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...

and purine/pyrimidine metabolism, urea cycle, haeme biosynthesis,

protein synthesis Protein biosynthesis, or protein synthesis, is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a number of critica ...

, and

protein folding Protein folding is the physical process by which a protein, after Protein biosynthesis, synthesis by a ribosome as a linear chain of Amino acid, amino acids, changes from an unstable random coil into a more ordered protein tertiary structure, t ...

. It can not reproduce on its own and relies on signals from the protist's nucleus. Isolated bacteria cannot survive on their own. When the bacteria are removed by antibiotic treatment, the protist survives but can not infect mosquitos. ''S. culicis'' has about 12,162 open reading frames (ORFs).

Symbiont

The bacterium Ca. '' Kinetoplastibacterium blastocrithidii'' is a ß-proteobacterium of the family Alcaligenaceae. It is enclosed in two layers of cell membranes, and unlike typical bacterial membrane,

peptidoglycan Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like layer (sacculus) that surrounds the bacterial cytoplasmic membrane. The sugar component consists of alternating ...

is greatly reduced. It acts as a cell organelle not only by supplying essential enzymes, but also by replacing paraflagellar rod associated to the axoneme, thus, intimately associated with 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 ...

. In addition, it provides surplus supply of ATP molecules for increased metabolic activities. During cell division, as the kinetoplast of the host divides so do the bacterium. The host cell controls the number of bacterial division. This coordinated mitosis results in even distribution of one bacterium in each daughter cell.

Ecology

''Strigomonas culicis'' can be found in several mosquito genera, such as ''

Anopheles ''Anopheles'' () is a genus of mosquito first described by the German entomologist Johann Wilhelm Meigen, J. W. Meigen in 1818, and are known as nail mosquitoes and marsh mosquitoes. Many such mosquitoes are Disease vector, vectors of the paras ...

'', '' Culex'', ''

'' and '' Coquillettidia''.

References

{{Taxonbar, from=Q56324252 Protists described in 1907 Trypanosomatida Endosymbiotic events Euglenozoa species