''Strigomonas culicis'' is a protist and member of

flagellated A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

trypanosomatid Trypanosomatida is a group of kinetoplastid excavates distinguished by having only a single flagellum. The name is derived from the Greek ''trypano'' (borer) and ''soma'' (body) because of the corkscrew-like motion of some trypanosomatid species ...

s. It is an obligate parasite in the gastrointestinal tract of mosquito, and is in turn a host to

symbiotic Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasi ...

bacteria. It maintains strict mutualistic relationship with the bacteria as a sort of cell organelle ( endosymbiont) so that it cannot lead an independent life without the bacteria. This and other symbiont-harbouring trypanosomatids such as ''

Angomonas deanei ''Angomonas deanei'' is a flagellated trypanosomatid protozoan. As an obligate parasite, it infects the gastrointestinal tract of insects, and is in turn a host to symbiotic bacteria. The bacterial endosymbiont ''Ca.'' "''Kinetoplastibacterium cr ...

'' are considered as "excellent models for the study of cell evolution because the host protozoan

co-evolve In biology, coevolution occurs when two or more species reciprocally affect each other's evolution through the process of natural selection. The term sometimes is used for two traits in the same species affecting each other's evolution, as well ...

s with an intracellular bacterium in a mutualistic relationship", and "the origin of new organelles" (i.e. symbiogenesis). Originally described as ''Blastocrithidia culicis'' in 1961, it was renamed ''Strigomonas culicis'' in 2011 upon establishing its genetic relationship with other related protists. 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 tha ...

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

Taxonomy

''S. culicis'' was originally described as ''Blastocrithidia culicis'' by F.G. Wallace and A. Johnson in 1961. It was later considered to be the same (synonym) as ''Trypanosoma'' (''Herpetomonas'') ''culicis,'' a species described by Frederick G. Novy, Ward J. MacNeal, and Harry N. Torreyin 1907. The species name refers to the mosquito ''

Culex ''Culex'' is a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nile virus, Japanese ence ...

'' in which it was found. But it is also present in other mosquitos such as ''

Aedes ''Aedes'' is a genus of mosquitoes originally found in tropical and subtropical zones, but now found on all continents except perhaps Antarctica. Some species have been spread by human activity: ''Aedes albopictus'', a particularly invasive spe ...

''. When Marta M.G. Teixeira and co-workers analysed the species in 2011 along with related protists such as ''

'' using molecular techniques, it was resolved that it belonged to an already existing genus ''Strigomonas''.

Biology

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

haemocoel The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

) and finally reside in the

salivary glands The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary glan ...

. 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 Amino acid synthesis is the set of biochemical processes (metabolic pathways) by which the amino acids are produced. The substrates for these processes are various compounds in the organism's diet or growth media. Not all organisms are able to sy ...

, lipid 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 critical ...

, and protein folding. 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).

Symbioant

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 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 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 provide motility. The axoneme ...

, thus, intimately associated with the

kinetoplast A kinetoplast is a network of circular DNA (called kDNA) inside a large 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. Kinetop ...

. 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.

References

{{Taxonbar, from=Q56324252 Protists described in 1961 Protists described in 2011 Kinetoplastids Endosymbiotic events