1.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
2.
Opisthokont
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The opisthokonts, sometimes referred to as the Fungi/Metazoa group, are generally recognized as a monophyletic clade. One common characteristic of opisthokonts is that flagellate cells, such as the sperm of most animals and it is this feature that gives the group its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more anterior flagella, in some opisthokont groups, including most of the fungi, flagellate cells have been lost. The close relationship between animals and fungi was suggested by Thomas Cavalier-Smith in 1987, who used the informal name opisthokonta, early phylogenies placed fungi near the plants and other groups that have mitochondria with flat cristae, but this character varies. Animals and fungi are more closely related to amoebas than they are to plants. Opisthokonts are divided into Holomycota or Nucletmycea and Holozoa, no opisthokonts basal to the Holomycota/Holozoa split have yet been identified, however, a 2013 study suggests that there may be many more unicellular opisthokonts than previously suspected. Holomycota and Holozoa are composed of the following groups, the choanoflagellates have a circular mitochondrial DNA genome with long intergenic regions. This is four times as large as animal mitochondrial genomes and contains twice as many protein genes, the ichthyosporeans have a two amino acid deletion in their elongation factor 1 α gene that is considered characteristic of fungi. The ichthyosl genome is >200 kilobase pairs in length and consists of several hundred linear chromosomes that share elaborate terminal-specific sequence patterns
3.
Fungus
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A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from the other eukaryotic life kingdoms of plants, a characteristic that places fungi in a different kingdom from plants, bacteria and some protists, is chitin in their cell walls. Similar to animals, fungi are heterotrophs, they acquire their food by absorbing dissolved molecules, growth is their means of mobility, except for spores, which may travel through the air or water. Fungi are the principal decomposers in ecological systems and this fungal group is distinct from the structurally similar myxomycetes and oomycetes. The discipline of biology devoted to the study of fungi is known as mycology, in the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more closely related to animals than to plants. Abundant worldwide, most fungi are inconspicuous because of the size of their structures. Fungi include symbionts of plants, animals, or other fungi and they may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform a role in the decomposition of organic matter and have fundamental roles in nutrient cycling. Since the 1940s, fungi have been used for the production of antibiotics, Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans, losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies. The fungus kingdom encompasses a diversity of taxa with varied ecologies, life cycle strategies. However, little is known of the biodiversity of Kingdom Fungi. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace, a group of all the fungi present in a particular area or geographic region is known as mycobiota, e. g. the mycobiota of Ireland. Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies. The fungi are now considered a kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago. Fungi have membrane-bound cytoplasmic organelles such as mitochondria, sterol-containing membranes and they have a characteristic range of soluble carbohydrates and storage compounds, including sugar alcohols, disaccharides, and polysaccharides
4.
Parasitism
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In biology/ecology, parasitism is a non-mutual relationship between species, where one species, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred primarily to organisms visible to the naked eye, Parasites can be microparasites, which are typically smaller, such as protozoa, viruses, and bacteria. Examples of parasites include the plants mistletoe and cuscuta, and animals such as hookworms, unlike predators, parasites typically do not kill their host, are generally much smaller than their host, and will often live in or on their host for an extended period. Both are special cases of consumer-resource interactions, Parasites show a high degree of specialization, and reproduce at a faster rate than their hosts. Classic examples of parasitism include interactions between vertebrate hosts and tapeworms, flukes, the Plasmodium species, and fleas, parasitism differs from the parasitoid relationship in that parasitoids generally kill their hosts. Parasites reduce host biological fitness by general or specialized pathology, such as parasitic castration and impairment of secondary sex characteristics, Parasites increase their own fitness by exploiting hosts for resources necessary for their survival, e. g. food, water, heat, habitat, and transmission. Although parasitism applies unambiguously to many cases, it is part of a continuum of types of interactions between species, rather than an exclusive category, in many cases, it is difficult to demonstrate harm to the host. In others, there may be no apparent specialization on the part of the parasite, coined in English in 1611, the word parasitism comes from the Greek παρά + σιτισμός feeding, fattening. Parasites are classified based on their interactions with their hosts and on their life cycles, an obligate parasite is totally dependent on the host to complete its life cycle, while a facultative parasite is not. A direct parasite has one host while an indirect parasite has multiple hosts. For indirect parasites, there always be a definitive host. Parasites that live on the outside of the host, either on the skin or the outgrowths of the skin, are called ectoparasites and those that live inside the host are called endoparasites. Endoparasites can exist in one of two forms, intercellular parasites or intracellular parasites, intracellular parasites, such as protozoa, bacteria or viruses, tend to rely on a third organism, which is generally known as the carrier or vector. The vector does the job of transmitting them to the host, an example of this interaction is the transmission of malaria, caused by a protozoan of the genus Plasmodium, to humans by the bite of an anopheline mosquito. Those parasites living in a position, being half-ectoparasites and half-endoparasites, are called mesoparasites. An epiparasite is one that feeds on another parasite and this relationship is also sometimes referred to as hyperparasitism, exemplified by a protozoan living in the digestive tract of a flea living on a dog. Social parasites take advantage of interactions between members of social organisms such as ants, termites, and bumblebees, an extreme example of social parasitism is the ant species of Tetramorium inquilinum of the Alps, which spend their whole lives on the back of Tetramorium host ants. With tiny and deprecated bodies they have evolved for one single task, if they fall off, they most likely would not have the strength to climb back on top of another ant, and eventually they will die
5.
Chytridiomycota
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Chytridiomycota is a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Greek χυτρίδιον chytridion, meaning little pot, chytrids are saprobic, degrading refractory materials such as chitin and keratin, and sometimes act as parasites. There has been a significant increase in the research of chytrids since the discovery of Batrachochytrium dendrobatidis, species of Chytridiomycota have traditionally been delineated and classified based on development, morphology, substrate, and method of zoospore discharge. However, single spore isolates display a great amount of variation in many of features, thus. Currently, taxonomy in Chytridiomycota is based on data, zoospore ultrastructure and some aspects of thallus morphology. In an older and more restricted sense, the term chytrids referred just to those fungi in the class Chytridiomycetes, here, the term “chytrid” refers to all members of Chytridiomycota. The chytrids have also included among the Protoctista, but are now regularly classed as fungi. In older classifications, chytrids, except the recently established order Spizellomycetales, were placed in the class Phycomycetes under the subphylum Myxomycophyta of the kingdom Fungi, previously, they were placed in the Mastigomycotina as the class Chytridiomycetes. The other classes of the Mastigomycotina, the Hyphochytriomycetes and Oomycetes, the class Chytridiomycetes has over 750 chytrid species distributed among ten orders. Additional classes include the Monoblepharidomycetes, with two orders, and the Hyaloraphidiomycetes with a single order, the Olpidiaceae, including the type genus Olpidium, formerly classified in the order Chytridiales, were raised to a separate phylum, the Olpidiomycota. Chytridiomycota are unusual among the Fungi in that they reproduce with zoospores, for most members of Chytridiomycetes, sexual reproduction is not known. Asexual reproduction occurs through the release of zoospores derived through mitosis, where it has been described, sexual reproduction of Chytridomycetes occurs via a variety of methods. It is generally accepted that the zygote forms a resting spore. In some members, sexual reproduction is achieved through the fusion of isogametes and this group includes the notable plant pathogens Synchytrium. Some algal parasites practice oogamy, a male gamete attaches itself to a nonmotile structure containing the female gamete. In another group, two thalli produce tubes that fuse and allow the gametes to meet and fuse, in the last group, rhizoids of compatible strains meet and fuse. Both nuclei migrate out of the zoosporangium and into the conjoined rhizoids where they fuse, the resulting zygote germinates into a resting spore. Sexual reproduction is common and well known members of the Monblepharidomycetes
6.
Flagellum
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A flagellum is a lash-like appendage that protrudes from the cell body of certain prokaryotic and eukaryotic cells. The word flagellum in Latin means whip, the primary role of the flagellum is locomotion, but it also often has function as a sensory organelle, being sensitive to chemicals and temperatures outside the cell. Flagella are organelles defined by function rather than structure, large differences occur between different types of flagella, the prokaryotic and eukaryotic flagella differ greatly in protein composition, structure, and mechanism of propulsion. However, both can be used for swimming, an example of a flagellated bacterium is the ulcer-causing Helicobacter pylori, which uses multiple flagella to propel itself through the mucus lining to reach the stomach epithelium. An example of a eukaryotic cell is the mammalian sperm cell. Eukaryotic flagella are structurally identical to eukaryotic cilia, although distinctions are made according to function and/or length. Fimbriae and pili are also thin appendages, but have different functions and are usually smaller, three types of flagella have so far been distinguished, bacterial, archaeal, and eukaryotic. The main differences among these three types are, Bacterial flagella are helical filaments, each with a motor at its base which can turn clockwise or counterclockwise. They provide two of several kinds of bacterial motility, archaeal flagella are superficially similar to bacterial flagella, but are different in many details and considered non-homologous. Eukaryotic flagella—those of animal, plant, and protist cells—are complex cellular projections that lash back, eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility. Primary cilia are immotile, and are not undulipodia, they have a structurally different 9+0 axoneme rather than the 9+2 axoneme found in both flagella and motile cilia undulipodia, the bacterial flagellum is made up of the protein flagellin. Its shape is a 20-nanometer-thick hollow tube and it is helical and has a sharp bend just outside the outer membrane, this hook allows the axis of the helix to point directly away from the cell. A shaft runs between the hook and the body, passing through protein rings in the cells membrane that act as bearings. Gram-positive organisms have two of these basal body rings, one in the layer and one in the plasma membrane. The filament ends with a capping protein, the flagellar filament is the long, helical screw that propels the bacterium when rotated by the motor, through the hook. Each protofilament is a series of protein chains. However, Campylobacter jejuni has seven protofilaments, the basal body has several traits in common with some types of secretory pores, such as the hollow, rod-like plug in their centers extending out through the plasma membrane. The bacterial flagellum is driven by an engine made up of protein
7.
Ascomycota
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Ascomycota is a division or phylum of the kingdom Fungi that, together with the Basidiomycota, form the subkingdom Dikarya. Its members are known as the sac fungi or ascomycetes. They are the largest phylum of Fungi, with over 64,000 species, the defining feature of this fungal group is the ascus, a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle, the ascomycetes are a monophyletic group, i. e. it contains all descendants of one common ancestor. Familiar examples of sac fungi include morels, truffles, brewers yeast and bakers yeast, dead mans fingers, the fungal symbionts in the majority of lichens such as Cladonia belong to the Ascomycota. There are many plant-pathogenic ascomycetes, including apple scab, rice blast, the fungi, black knot. Several species of ascomycetes are biological model organisms in laboratory research, most famously, Neurospora crassa, several species of yeasts, and Aspergillus species are used in many genetics and cell biology studies. Penicillium species on cheeses and those producing antibiotics for treating infectious diseases are examples of taxa that belong to the Ascomycota. They are fungi which produce microscopic spores inside special, elongated cells or sacs, known as asci, Asexual reproduction, Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. Asexual reproduction of ascomycetes is very diverse from both structural and functional points of view, the most important and general is production of conidia, but chlamydospores are also frequently produced. Furthermore, Ascomycota also reproduce asexually through budding, 1) Conidia formation, Asexual reproduction may occur through vegetative reproductive spores, the conidia. Asexual, non-motile haploid spore of a fungus, which is named after the Greek word for dust, conia and they are typically formed at the ends of specialized hyphae, the conidiophores. Depending on the species they may be dispersed by wind or water, conidiophores may simply branch off from the mycelia or they may be formed in fruiting bodies. The hypha that creates the sporing tip can be similar to the normal hyphal tip. The most common differentiation is the formation of a bottle shaped cell called a phialide, as all of these asexual structures are not single hyphae. In some groups, the conidiophores are aggregated to form a thick structure, in the order Moniliales, all of them are single hyphae with the exception of the aggregations, termed as coremia or synnema. These produce structures rather like corn-stokes, with many conidia being produced in a mass from the aggregated conidiophores, the diverse conidia and conidiophores sometimes develop in asexual sporocarps with different characteristics. Some species of Ascomycetes form their structures within plant tissue, either as parasite or saprophytes and these fungi have evolved more complex asexual sporing structures, probably influenced by the cultural conditions of plant tissue as a substrate
8.
Yeast
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Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The yeast lineage originated hundreds of millions of years ago, and 1,500 species are currently identified and they are estimated to constitute 1% of all described fungal species. Yeast sizes vary greatly, depending on species and environment, typically measuring 3–4 µm in diameter, most yeasts reproduce asexually by mitosis, and many do so by the asymmetric division process known as budding. Yeasts, with their growth habit, can be contrasted with molds. Fungal species that can take both forms are called dimorphic fungi and it is also a centrally important model organism in modern cell biology research, and is one of the most thoroughly researched eukaryotic microorganisms. Researchers have used it to information about the biology of the eukaryotic cell. Other species of yeasts, such as Candida albicans, are opportunistic pathogens, yeasts have recently been used to generate electricity in microbial fuel cells, and produce ethanol for the biofuel industry. Yeasts do not form a taxonomic or phylogenetic grouping. The budding yeasts are classified in the order Saccharomycetales, within the phylum Ascomycota, the word yeast comes from Old English gist, gyst, and from the Indo-European root yes-, meaning boil, foam, or bubble. Yeast microbes are probably one of the earliest domesticated organisms, archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeast-raised bread, as well as drawings of 4, 000-year-old bakeries and breweries. In 1680, Dutch naturalist Anton van Leeuwenhoek first microscopically observed yeast, but at the time did not consider them to be living organisms, researchers were doubtful whether yeasts were algae or fungi, but in 1837 Theodor Schwann recognized them as fungi. In 1857, French microbiologist Louis Pasteur proved in the paper Mémoire sur la fermentation alcoolique that alcoholic fermentation was conducted by living yeasts and not by a chemical catalyst. Pasteur showed that by bubbling oxygen into the yeast broth, cell growth could be increased, by the late 18th century, two yeast strains used in brewing had been identified, Saccharomyces cerevisiae and S. carlsbergensis. S. cerevisiae has been sold commercially by the Dutch for bread-making since 1780, while, around 1800, in 1825, a method was developed to remove the liquid so the yeast could be prepared as solid blocks. The industrial production of yeast blocks was enhanced by the introduction of the press in 1867. In 1872, Baron Max de Springer developed a process to create granulated yeast. Yeasts are chemoorganotrophs, as they use organic compounds as a source of energy, carbon is obtained mostly from hexose sugars, such as glucose and fructose, or disaccharides such as sucrose and maltose. Some species can metabolize pentose sugars such as ribose, alcohols, Yeast species either require oxygen for aerobic cellular respiration or are anaerobic, but also have aerobic methods of energy production
9.
Hypha
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A hypha is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the mode of vegetative growth. Yeasts are unicellular fungi that do not grow as hyphae, a hypha consists of one or more cells surrounded by a tubular cell wall. In most fungi, hyphae are divided into cells by internal cross-walls called septa, septa are usually perforated by pores large enough for ribosomes, mitochondria and sometimes nuclei to flow between cells. The major structural polymer in fungal cell walls is typically chitin, in contrast to plants, some fungi have aseptate hyphae, meaning their hyphae are not partitioned by septa. Hyphae have a diameter of 4-6 µm. During tip growth, cell walls are extended by the assembly and polymerization of cell wall components. The spitzenkörper is an intracellular organelle associated with tip growth and it is composed of an aggregation of membrane-bound vesicles containing cell wall components. The spitzenkörper is part of the system of fungi, holding and releasing vesicles it receives from the Golgi apparatus. These vesicles travel to the membrane via the cytoskeleton and release their contents outside the cell by the process of exocytosis. Vesicle membranes contribute to growth of the membrane while their contents form new cell wall. As a hypha extends, septa may be formed behind the tip to partition each hypha into individual cells. Hyphae can branch through the bifurcation of a tip, or by the emergence of a new tip from an established hypha. The direction of growth can be controlled by environmental stimuli. Hyphae can sense reproductive units from some distance, and grow towards them, hyphae can weave through a permeable surface to penetrate it. Hyphae may be modified in different ways to serve specific functions. Some parasitic fungi form haustoria that function in absorption within the host cells, the arbuscules of mutualistic mycorrhizal fungi serve a similar function in nutrient exchange, so are important in assisting nutrient and water absorption by plants. Hyphae are found enveloping the gonidia in lichens, making up a part of their structure
10.
Saccharomyces cerevisiae
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Saccharomyces cerevisiae is a species of yeast. It has been instrumental to winemaking, baking, and brewing since ancient times and it is believed to have been originally isolated from the skin of grapes. It is one of the most intensively studied model organisms in molecular and cell biology. It is the microorganism behind the most common type of fermentation, S. cerevisiae cells are round to ovoid, 5–10 μm in diameter. It reproduces by a process known as budding. Many proteins important in biology were first discovered by studying their homologs in yeast, these proteins include cell cycle proteins, signaling proteins. S. cerevisiae is currently the only yeast cell known to have Berkeley bodies present, antibodies against S. cerevisiae are found in 60–70% of patients with Crohns disease and 10–15% of patients with ulcerative colitis. Saccharomyces derives from Latinized Greek and means sugar-mold or sugar-fungus, saccharo being the combining form sugar, cerevisiae comes from Latin and means of beer. Refinements in microbiology following the work of Louis Pasteur led to more advanced methods of culturing pure strains, in 1879, Great Britain introduced specialized growing vats for the production of S. The company created yeast that would rise twice as fast, cutting down on baking time, lesaffre would later create instant yeast in the 1970s, which has gained considerable use and market share at the expense of both fresh and dry yeast in their various applications. In nature, yeast cells are primarily on ripe fruits such as grapes. Since S. cerevisiae is not airborne, it requires a vector to move, queens of social wasps overwintering as adults can harbor yeast cells from autumn to spring and transmit them to their progeny. The intestine of Polistes dominula, a wasp, hosts S. cerevisiae strains as well as S. cerevisiae × S. paradoxus hybrids. The optimum temperature for growth of S. cerevisiae is 30–35 °C, two forms of yeast cells can survive and grow, haploid and diploid. The haploid cells undergo a simple lifecycle of mitosis and growth and this is the asexual form of the fungus. The diploid cells undergo a simple lifecycle of mitosis and growth. The rate at which the cell cycle progresses often differs substantially between haploid and diploid cells. Under conditions of stress, diploid cells can undergo sporulation, entering meiosis and producing four haploid spores and this is the sexual form of the fungus
11.
Chitin
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Chitin n is a long-chain polymer of an N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. The structure of chitin is comparable to the cellulose, forming crystalline nanofibrils or whiskers. In terms of function, it may be compared to the protein keratin, chitin has proved versatile for several medicinal, industrial and biotechnological purposes. The English word chitin comes from the French word chitine, which first appeared in 1821 and derived from the Greek word χιτών, a similar word, chiton, refers to a marine animal with a protective shell. The structure of chitin was solved by Albert Hofmann in 1929, chitin is a modified polysaccharide that contains nitrogen, it is synthesized from units of N-acetyl-D-glucosamine. Therefore, chitin may be described as cellulose with one group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength, in its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. Combined with calcium carbonate, as in the shells of crustaceans and molluscs and this composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate. Another difference between pure and composite forms can be seen by comparing the body wall of a caterpillar to the stiff. The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry, scarab beetles in the genus Cyphochilus also utilize chitin to form extremely thin scales that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of nanometres, the multiple scattering of light is thought to play a role in the unusual whiteness of the scales. In addition, some wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes. Chitosan is produced commercially by deacetylation of chitin, chitosan is soluble in water, chitin producing organisms like protozoa, fungi, arthropods, and nematodes are often pathogens in other species. Keratinocytes in skin can also react to chitin or chitin fragments, according to in vitro studies, chitin is sensed by receptors, such as FIBCD1, KLRB1, REG3G, Toll-like receptor 2, CLEC7A, and mannose receptors. Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1, the first chitin receptor was cloned in 2006. When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, commensal fungi that have ways to interact with the host immune response that as of 2016 were not well understood. Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors, zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins, it is a major pest in wheat crops. Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites, the oldest preserved chitin dates to the Oligocene, about 25 million years ago, consisting of a scorpion encased in amber
12.
Microsporidia
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The Microsporidia constitute a group of spore-forming unicellular parasites. They were once considered protozoans or protists, but are now known to be fungi, loosely 1500 of the probably more than one million species are named now. Microsporidia are restricted to hosts, and all major groups of animals host microsporidia. Most infect insects, but they are responsible for common diseases of crustaceans. The named species of microsporidia usually infect one host species or a group of related taxa. Several species, most of which are opportunistic, also infect humans, approximately 10 percent of the species are parasites of vertebrates—including humans, in which they can cause microsporidiosis. After infection they influence their hosts in various ways and all organs and tissues are invaded, some species are lethal, and a few are used in biological control of insect pests. Parasitic castration, gigantism, or change of host sex are all potential effects of microsporidian parasitism, in the most advanced cases of parasitism the microsporidium rules the host cell completely and controls its metabolism and reproduction, forming a xenoma. Replication takes place within the cells, which are infected by means of unicellular spores. These vary from 1–40 μm, making some of the smallest eukaryotes. Microsporidia that infect mammals are 1. 0–4.0 μm and they also have the smallest eukaryotic genomes. The terms microsporidium and microsporidian are used as names for members of the group. The name Microsporidium Balbiani,1884 is also used as a genus for incertae sedis members. Microsporidia lack mitochondria, instead possessing mitosomes and they also lack motile structures, such as flagella. 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 anterior half of the spore contains a harpoon-like apparatus with a long, thread-like polar filament, 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, 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
. PMID 19939264.
