HOME

TheInfoList




Microsporidia are a group of
spore )'', growing on a thinning, thinned hybrid black poplar ''(populus, Populus x canadensis)''. The last stage of the moss#Life cycle, moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is ...
-forming
unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Or ...
parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is adaptation (biology), adapted structurally to this w ...
s. These spores contain an extrusion apparatus that has a coiled polar tube ending in an anchoring disc at the apical part of the spore. They were once considered
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of Unicellular organism, single-celled eukaryotes, either free-living or Parasitism, parasitic, that feed on organic matter such as other mi ...

protozoa
ns or
protist A protist () is any (that is, an organism whose contain a ) that is not an , , or . While it is likely that protists share a (the ), the exclusion of other eukaryotes means that protists do not form a natural group, or . Therefore, some pro ...
s, but are now known to be
fungi A fungus (plural The plural (sometimes abbreviated An abbreviation (from Latin ''brevis'', meaning ''short'') is a shortened form of a word or phrase, by any method. It may consist of a group of letters, or words taken from the full ...

fungi
, or a sister group to fungi. This type of fungi obligates eukaryotic parasites that use a unique mechanism to infect host cells. They have recently been discovered to infect
Coleoptera Beetles are a group of insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known a ...

Coleoptera
on a large scale, in a 2017 Cornell study. Loosely 1500 of the probably more than one million species are named. Microsporidia are restricted to animal
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 People *Jim Host (born 1937), American businessman *Michel Host (19 ...
s, and all major groups of animals host microsporidia. Most infect
insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Rom ...

insect
s, but they are also responsible for common diseases of
crustacea Crustaceans (Crustacea ) form a large, diverse arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Eua ...

crustacea
ns and
fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ray-finned fish, belonging to the class , with over 95 ...

fish
. The named species of microsporidia usually infect one host species or a group of closely related taxa. Approximately 10 percent of the species are parasites of vertebrates —several species, most of which are opportunistic, can infect humans, in whom they can cause
microsporidiosis Microsporidiosis is an opportunistic intestinal infection that causes diarrhea and wasting in immunocompromised individuals (HIV, for example). It results from different species of microsporidia, a group of microbial (unicellular) fungi. In HIV in ...
. After infection they influence their hosts in various ways and all organs and tissues are invaded, though generally by different species of microsporidia. Some species are lethal, and a few are used in biological control of insect pests.
Parasitic castrationParasitic castration is the strategy, by a parasite Parasitism is a symbiotic relationship between species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as wel ...
, gigantism, or change of host sex are all potential effects of microsporidian parasitism (in insects). In the most advanced cases of parasitism the microsporidium rules the host cell completely and controls its metabolism and reproduction, forming a xenoma.Ronny Larsson, Lund University (Department of Cell and Organism Biology
''Cytology and taxonomy of the microsporidia''
2004.
Replication takes place within the host's cells, which are infected by means of unicellular
spore )'', growing on a thinning, thinned hybrid black poplar ''(populus, Populus x canadensis)''. The last stage of the moss#Life cycle, moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is ...
s. These vary from 1–40 μm, making them some of the smallest
eukaryote Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), tax ...

eukaryote
s. Microsporidia that infect
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s are 1.0–4.0 μm. They also have the smallest eukaryotic
genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The genome includes both the genes (the coding regions) and the noncodin ...

genome
s. The terms "microsporidium" (pl. "microsporidia") and "microsporidian" are used as vernacular names for members of the group. The name ''Microsporidium'' Balbiani, 1884 is also used as a catchall genus for
incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
members.


Morphology

Microsporidia lack
mitochondria A mitochondrion (; ) is a double-membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, i ...

mitochondria
, instead possessing
mitosome A mitosome is an 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 ( ...
s. They also lack motile structures, such as
flagella A flagellum (; ) is a hairlike appendage that protrudes from a wide range of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism () is any organic, life, living system that fu ...
. Microsporidia produce highly resistant spores, capable of surviving outside their host for up to several years. Spore morphology is useful in distinguishing between different species. Spores of most species are oval or pyriform, but rod-shaped or spherical spores are not unusual. A few genera produce spores of unique shape for the genus. The spore is protected by a wall, consisting of three layers: *an outer electron-dense ''exospore'' *a median, wide and seemingly structureless ''endospore'', containing
chitin units that repeat to form long chains in β-(1→4)-linkage. of the chitin molecule. Chitin ( carbon, C8H13O5N)n ( ) is a long-chain polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical su ...

chitin
*a thin internal ''plasma membrane'' In most cases there are two closely associated
nuclei ''Nucleus'' (plural 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 ...

nuclei
, forming a '' diplokaryon'', but sometimes there is only one.
The anterior half of the spore contains a harpoon-like apparatus with a long, thread-like ''polar filament'', which is coiled up in the posterior half of the spore. The anterior part of the polar filament is surrounded by a ''polaroplast'', a lamella of membranes. Behind the polar filament, there is a posterior ''vacuole''.


Infection

In the gut of the host the spore germinates, it builds up osmotic pressure until its rigid wall ruptures at its thinnest point at the apex. The posterior vacuole swells, forcing the polar filament to rapidly eject the infectious content into the cytoplasm of the potential host. Simultaneously the material of the filament is rearranged to form a tube which functions as a hypodermic needle and penetrates the gut epithelium. Once inside the host cell, a
sporoplasm Sporoplasm is an infectious material present in the cytoplasm of various Fungus, fungi-like organisms, such as members of class ''Microsporidia''. Sporoplasm is defined as a mass of protoplasm that gives rise to or forms a spore. The protoplasmic ...
grows, dividing or forming a
multinucleate Multinucleate cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a roo ...
plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a Hematophagy, blood-feeding insect host (biology), host which then inj ...
, before producing new spores. The life cycle varies considerably. Some have a simple asexual life cycle, while others have a complex life cycle involving multiple hosts and both asexual and
sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Greek, ...
. Different types of spores may be produced at different stages, probably with different functions including autoinfection (transmission within a single host).


Medical implications

In animals and humans, microsporidia often cause chronic, debilitating diseases rather than lethal infections. Effects on the host include reduced longevity, fertility, weight, and general vigor.
Vertical transmissionVertical transmission of symbionts Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction In ecology Ecology (from el, οἶκος, "house" ...
of microsporidia is frequently reported. In the case of insect hosts, vertical transmission often occurs as transovarial transmission, where the microsporidian parasites pass from the ovaries of the female host into eggs and eventually multiply in the infected larvae. '' Amblyospora salinaria'' n. sp. which infects the mosquito '' Culex salinarius'' Coquillett, and '' Amblyospora californica'' which infects the mosquito '' Culex tarsalis'' Coquillett, provide typical examples of transovarial transmission of microsporidia. Microsporidia, specifically the mosquito-infecting '' Vavraia culicis'', are being explored as a possible 'evolution-proof' malaria-control method. Microsporidian infection of ''
Anopheles gambiae The ''Anopheles gambiae'' complex consists of at least seven morphologically indistinguishable species of mosquitoes in the genus '' Anopheles''. The complex was recognised in the 1960s and includes the most important vectors of malaria ...

Anopheles gambiae
'' (the principal vector of ''
Plasmodium falciparum ''Plasmodium falciparum'' is a unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All org ...

Plasmodium falciparum
'' malaria) reduces malarial infection within the mosquito, and shortens the mosquito lifespan. As the majority of malaria-infected mosquitoes naturally die before the malaria parasite is mature enough to transmit, any increase in mosquito mortality through microsporidian-infection may reduce malaria transmission to humans. In May 2020, researchers reported that ''Microsporidia MB'', a symbiont in the midgut and ovaries of '' An. arabiensis'', significantly impaired transmission of ''P. falciparum'', had "no overt effect" on the fitness of host mosquitoes, and was transmitted vertically (through inheritance).


Clinical

Microsporidian infections of humans sometimes cause a disease called
microsporidiosis Microsporidiosis is an opportunistic intestinal infection that causes diarrhea and wasting in immunocompromised individuals (HIV, for example). It results from different species of microsporidia, a group of microbial (unicellular) fungi. In HIV in ...
. At least 14 microsporidian species, spread across eight genera, have been recognized as human
pathogen In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
s. These include '' Trachipleistophora hominis''.


As hyperparasites

Microsporidia can infect a variety of hosts, including hosts which are themselves parasites. In that case, the microsporidian species is a
hyperparasite A hyperparasitic microsporidian, ''Nosema podocotyloidis'', a parasite of a digenean, ''Podocotyloides magnatestis'', itself a parasite of the fish ''Parapristipoma octolineatum'' A hyperparasite is a parasite whose Host (biology) , host, often an ...
, i.e. a parasite of a parasite. As an example, more than eighteen species are known which parasitize
digenea Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a Class (biology), class of Trematoda, trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytium, syncytial tegument (helminth), tegu ...
ns (parasitic
flatworm The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a count ...

flatworm
s). These digeneans are themselves parasites in various
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s and
mollusc Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
s. Eight of these species belong to the genus '' Nosema''.


Genomes

Microsporidia have the smallest known (nuclear) eukaryotic
genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The genome includes both the genes (the coding regions) and the noncodin ...

genome
s. The parasitic lifestyle of microsporidia has led to a loss of many
mitochondria A mitochondrion (; ) is a double-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. Biological membranes include cell membranes ...

mitochondria
l and genes, and even their
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
s are reduced in size compared with those of most
eukaryote Eukaryotes () are organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biology), tax ...

eukaryote
s. As a consequence, the genomes of microsporidia are much smaller than those of other eukaryotes. Currently known microsporidial genomes are 2.5 to 11.6 Mb in size, encoding from 1,848 to 3,266 proteins which is in the same range as many
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
.
Horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient G ...
(HGT) seems to have occurred many times in microsporidia. For instance, the genomes of '' Encephalitozoon romaleae'' and '' Trachipleistophora hominis'' contain genes that derive from animals and bacteria, and some even from fungi.


Classification

The first described microsporidian genus, '' Nosema'', was initially put by Nägeli in the fungal group Schizomycetes together with some
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
and
yeasts Yeasts are eukaryotic Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It ...
. For some time microsporidia were considered as very primitive eukaryotes, placed in the protozoan group Cnidospora. Later, especially because of the lack of mitochondria, they were placed along with the other
Protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of single-celled eukaryote Eukaryotes () are organism In biology, an organism () is any organic, life, living system that ...

Protozoa
such as
diplomonad The diplomonads (Greek for "two units") are a group of flagellate 's '' Artforms of Nature'', 1904 (''Giardia lamblia'') ('' Chlamydomonas'') A flagellate is a cell or organism with one or more whip-like Appendage, appendages called flagellum, ...
s, parabasalids and
archamoebae The Archamoebae are a group of protist A protist () is any eukaryotic organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biolog ...
in the
protozoa Protozoa (singular protozoon or protozoan, plural protozoa or protozoans) is an informal term for a group of Unicellular organism, single-celled eukaryotes, either free-living or Parasitism, parasitic, that feed on organic matter such as other mi ...

protozoa
n-group Archezoa. More recent research has falsified this theory of early origin (for all of these). Instead, microsporidia are proposed to be highly developed and specialized organisms, which just dispensed functions that are needed no longer, because they are supplied by the host. Furthermore, spore-forming organisms in general do have a complex system of reproduction, both sexual and asexual, which look far from primitive. Since the mid-2000s microsporidia are placed within the Fungi or as a sister-group of the Fungi with a common ancestor. Work to identify clades is largely based on habitat and host. Three classes of Microsporidia are proposed by Vossbrinck and Debrunner-Vossbrinck, based on the habitat: Aquasporidia, Marinosporidia and Terresporidia. A second classification by Cavalier-Smith 1993: * Subphyla Rudimicrospora Cavalier-Smith 1993 ** Class Minisporea Cavalier-Smith 1993 *** Order Minisporida Sprague, 1972 ** Class Metchnikovellea Weiser, 1977 *** Order Metchnikovellida Vivier, 1975 * Subphyla Polaroplasta Cavalier-Smith 1993 ** Class Pleistophoridea Cavalier-Smith 1993 *** Order Pleistophorida Stempell 1906 ** Class Disporea Cavalier-Smith 1993 *** Subclass Unikaryotia Cavalier-Smith 1993 *** Subclass Diplokaryotia Cavalier-Smith 1993


See also

* List of Microsporidian genera * '' Glugea'', a genus of microsporidia * ''
Nosema apis ''Nosema apis'' is a microsporidia Microsporidia are a group of spore-forming unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism (from Ancient Greek, Greek: ὀργαν ...
'', a microsporidian parasite of bees


References


External links


BioHealthBase Bioinformatics Resource Center
Database of microspordia sequences and related information. * {{Taxonbar, from=Q132652 Fungus phyla Fungi by classification