The fungal cell wall in the Kingdom Fungi is composed of chitin and glucans in Ascomycota, Basidiomycota and Chytridiomycota as well as chitosan and other components in Zygomycota Kirk et al. Hyphae can have cross walls called septa , or lack cross walls nonseptate; aseptate; coenocytic. The type of hyphae— septate or aseptate —is characteristic of specific groups of fungi.
In fungi that form septate hyphae, there are perforations at the septa, called septal pores, which allow the movement of cytoplasm and organelles from one compartment to the next. The type and complexity of the septal pore is characteristic of specific groups of fungi. Hyphae grow from a germinating spore or other type of propagule, and these are described in more detail in the section "Fungal Reproduction. As a result of apical growth, hyphae are relatively uniform in diameter, and mycelium that grows in an unimpeded manner forms a circular colony on solid substrates that support fungal growth; agar, a gelatinous material derived from seaweed, amended with different types of nutrients is commonly used to grow fungi in culture Fig.
Some fungi grow exclusively or mostly as yeasts , defined as single-celled fungi that reproduce by budding or fission. In contrast to apical growth that is characteristic of hyphae, yeasts exhibit wall growth over the entire cell surface, often resulting in a nearly spherical cell Fig.
There are also fungi that can switch between mycelial growth and yeast-like growth, dependent upon the environmental conditions. The ability to grow in different forms is called dimorphism, and is exhibited by some members of phyla Ascomycota, Basidiomycota and Zygomycota. Most of the organelles present in fungal cells are similar to those of other eukaryotes. Fungi have been found to possess between 6 and 21 chromosomes coding for 6, to nearly 18, genes.
Genome sizes range from 8. Many fungi Ascomycota have a life cycle that is predominantly haploid, while others Basidiomycota have a long dikaryotic phase. Fungi frequently reproduce by the formation of spores. A spore is a survival or dispersal unit, consisting of one or a few cells, that is capable of germinating to produce a new hypha. Unlike plant seeds, fungal spores lack an embryo, but contain food reserves needed for germination. Many fungi produce more than one type of spore as part of their life cycles.
Fungal spores may be formed via an asexual process involving only mitosis mitospores , or via a sexual process involving meiosis meiospores. The manner in which meiospores are formed reflects the evolutionary history and thus the classification for the major groups phyla of fungi.
Many fungi produce spores inside or upon a fruiting body. Many people are familiar with the mushroom, a type of fruiting body produced by some Basidiomycota. You may recognize other fungal fruiting bodies such as puffballs, or shelf fungi. These are examples of large, conspicuous fruiting bodies, but there is an even greater diversity of microscopic fruiting bodies produced by various fungi.
What all fruiting bodies have in common is that they produce spores and provide a mechanism for dispersing those spores. Fruiting bodies will be discussed in more detail within the fungal groups. Many fungi are able to reproduce by both sexual and asexual processes. Sexual and asexual reproduction may require different sets of conditions e.
In some fungi, two sexually compatible strains must conjugate mate in order for sexual reproduction to occur. The terms ' anamorph ' and ' teleomorph ' are used to convey the asexual and sexual reproduction morphological types, respectively, in a particular fungus.
The concept of anamorph and teleomorph is a confusing one for many students, as we are not accustomed to thinking about organisms with such reproductive flexibility.
For a more thorough discussion of anamorph and teleomorph, refer to Alexopoulos et al. Examples of meiospores—spores that are the products of meiosis—include ascospores see Ascomycota and basidiospores see Basidiomycota. Ascospores are formed inside a sac-like structure called an ascus Fig. An ascus starts out as a sac of cytoplasm and nuclei, and by a process called "free cell formation" Kirk et al. Ascospores vary in size, shape, color, septation, and ornamentation among taxa.
Basidiospores are formed on a basidium Fig. Basidiospores vary in size, color and ornamentation depending upon the taxonomic group. More information on dispersal of ascospores and basidiospores can be found below. Examples of mitospores are conidia sing. Another type of asexual propagule produced by fungi in several different phyla is the chlamydospore. Conidia are formed from a modified hypha or a differentiated conidiogenous cell of the fungus.
Conidiogenous cells can be formed singly on hyphae, on the surface of aggregated hyphal structures, or within different types of fruiting bodies. Fruiting bodies inside which conidia are formed are pycnidia and acervuli. Sporodochia and synnemata are examples of fruiting bodies on which conidia are formed. Conidia are produced primarily by Ascomycota, although some Basidiomycota are capable of producing them as well.
Sporangiospores are asexual propagules formed inside a globose or cylindrical sporangium by a process involving cleavage of the cytoplasm. Sporangiospores are thin-walled, one-celled, hyaline or pale-colored, and are usually globose or ellipsoid in shape. One to 50, sporangiospores may be formed in a single sporangium. When mature, sporangiospores are released by breakdown of the sporangial wall, or the entire sporangium may be dispersed as a unit.
Sporangiospores are produced by fungi in phyla Chytridiomycota and Zygomycota, as well fungal-like Oomycetes see section "Fungal-like Organisms Studied by Plant Pathologists and Mycologists". A zoospore is a microscopic, motile propagule, approx.
Zoospores are produced by one group of true Fungi Chytridiomycota , and by fungal-like organisms in Kingdom Straminipila and some slime molds see section "Fungal-like Organisms Studied by Plant Pathologists and Mycologists".
Two types of flagella are known—the whiplash flagellum, which is directed backward, and the tinsel flagellum, which is directed forward. The tinsel flagellum is only present in members of Kingdom Straminipila and does not occur in true fungi. The length of time zoospores are able to swim is determined by their endogenous energy reserves—zoospores cannot obtain food from external sources—and environmental conditions.
Zoospores may exhibit chemotaxis—movement in response to a chemical gradient, e. At the end of its motile phase, the zoospore undergoes a process called encystment in which it either sheds or retracts the flagella and produces a cell wall. The encysted zoospore, called a cyst, may germinate directly by the formation of a germ tube , or indirectly by the emergence of another zoospore. Zoospores are formed inside a sac-like structure called a zoosporangium by a process involving mitosis and cytoplasmic cleavage—similar to the formation of sporangiospores in sporangia.
Depending upon the taxonomic group, zoospores emerge from the zoosporangium through breakdown of the zoosporangial wall, through a preformed opening in the wall covered with a cap called an operculum that flips back, or by a gelatinous plug that dissolves.
Chamydospores are survival propagules formed from an existing hyphal cell or a conidium that develops a thickened wall and cytoplasm packed with lipid reserves.
The thickened cell walls may be pigmented or hyaline, and chlamydospores develop singly or in clusters, depending upon the fungus. Chlamydospores are passively dispersed, in most instances when the mycelium breaks down. Chlamydospores are formed by many different groups of fungi and are often found in aging cultures. Sclerotia sing. Sclerotia contain food reserves, and are a type of survival propagule produced by a number of fungi in phyla Ascomycota and Basidiomycota; in some fungi, such as Rhizoctonia solani , they are the only type of propagule produced, whereas in fungi such as Claviceps purpurea and Sclerotinia sclerotiorum , they are overwintering structures that can germinate directly, or give rise to structures in which the meiospores are formed.
The characteristics and diversity of the major phyla of true Fungi will be briefly described. Selected representatives of the different phyla are introduced and, in many instances, illustrated. A generalized life cycle also is presented for each phylum that illustrates when plasmogamy cell fusion , karyogamy nuclear fusion and meiosis occur relative to each other, and the types of structures involved in these events. For more detailed information on members of Kingdom Fungi, recommended reading is provided at the end of this article.
Phylum Ascomycota is the largest group of fungi, with approximately 33, described species in three subphyla—Taphrinomycotina, Saccharomycotina, and Pezizomycotina. Members of this phylum reproduce sexually or meiotically Fig. Many species of Ascomycota also or exclusively produce spores through an asexual or mitotic process; these spores, called conidia , exhibit a wide range of size, shape, color and septation among the different fungi in which they are formed.
Conidia and ascospores are usually produced at different times of year, if ascospores are formed in the lifecycle. The existence of many Ascomycota having sexual and asexual states that are separated in time and space has long confused those new to mycology and plant pathology. The asexual states of Ascomycota are especially important to the plant pathologist because they are more commonly encountered than the sexual state, and must be identified for control, quarantine, or other purposes.
Fungi that reproduce only via asexual means have been given various designations including deuteromycetes, fungi imperfecti, mitosporic fungi, conidial fungi, and anamorphic fungi.
Subphylum Taphrinomycotina includes fungi that, with one known exception, do not form fruiting bodies—as examples, the fission yeast Schizosaccharomyces Fig. Subphylum Saccharomycotina contains approximately species of yeasts, most of which live as saprotrophs in association with plants and animals, but also including a small number of plant and animal pathogens Suh et al.
Asci are formed naked Fig. Yeasts traditionally have been important in the production of beer, wine, single cell protein and baker's yeast, but their role in industry has expanded to the production of citric acid, fuel alcohol, and riboflavin Kurtzman and Sugiyama Saccharomyces cerevisiae Fig.
In , S. Subphylum Pezizomycotina is the largest group in the phylum, with more than 32, identified species that occupy a wide range of ecological niches, occurring as saprotrophs, parasites and mutualists with plants, animals and other fungi. Three different types of asci occur in this subphylum, prototunicate, unitunicate and bitunicate. Prototunicate asci release ascospores by breakdown of the ascus wall, whereas in the unitunicate and bitunicate asci, the ascospores are forcibly discharged.
Bitunicate asci have an inner wall that balloons out from the outer wall prior to ascospore discharge, and in unitunicate asci the wall layers do not separate from each other. A wide range of fruiting bodies are formed by members of subphylum Pezizomycotina, including cleistothecia , chasmothecia , apothecia , perithecia and pseudothecia. Stromata , hardened masses of hyphae on or in which perithecia or pseudothecia are formed, occur in some members of this subphylum.
Cleistothecia sing. Common fungi that produce cleistothecia include the teleomorphic sexual states of Aspergillus and Penicillium Fig. Species of Aspergillus are important in the production of fermented foods and beverages, including soy sauce, miso and rice wine sake. Some species of Aspergillus infect animals, causing a disease known as aspergillosis, and others produce mycotoxins.
Aflatoxin is a potent carcinogen produced by A. The U. Food and Drug Administration established a strict limit of 20 parts per billion on aflatoxin levels in food, and the U.
Penicillium species are also used in food production. For example, the blue veins in Roquefort and Gorgonzola cheeses are due to the growth and sporulation of particular species of Penicillium Fig. The antibiotic penicillin, the "wonder drug" of the 20 th century, is produced by strains of P.
Other species of Penicillium, such as P. Chasmothecia sing. The term is now used to refer to the fruiting bodies of the powdery mildew fungi Fig. Apothecia sing. Apothecia-forming fungi are also called "cup fungi" or discomycetes. Some important groups of plant pathogens that form apothecia include species of Monilinia brown rot of peach; Figs.
Perithecia sing. Most fungi producing perithecia also have unitunicate asci and are classified in Sordariomycetes , one of the largest classes of Ascomycota with more than 3, described species Zhang et al. These fungi have also been called pyrenomycetes. Members of this group are common in nearly all ecosystems, where they occur as saprotrophs, endophytes of plants, or pathogens of plants, animals and other fungi.
A large number of economically important plant pathogens belong to Sordariomycetes, including those that cause anthracnose diseases Glomerella cingulata , blasts Magnaporthe oryzae , rice blast pathogen , blights Cryphonectria parasitica , chestnut blight , ergot Claviceps purpurea , and Fusarium head blight scab of small grains Gibberella zeae.
Pseudothecia sing. Asci form in locules openings inside vegetative fungal tissue called ascostroma ; this group has been called loculoascomycetes, but is now placed in class Dothideomycetes. Other characteristics of Dothideomycetes include the formation of bitunicate asci, and many members of this group produce darkly pigmented, multiseptate asospores or conidia.
Similar to the Sordariomycetes, members of Dothideomycetes occur in a wide range of habitats as saprotrophs and associate with plants as pathogens, endophytes and growing on the surface of plants as epiphytes Schoch et al. Examples of well-known plant pathogens belonging to this group include Venturia inaequalis apple scab; Fig.
Most of the lichen-forming members of Ascomycota belong in class Lecanoromycetes. This is the largest class of fungi, with over 13, described species Miadlikowska et al. Most of the members of this class produce apothecial fruiting bodies Figs. The lichen thallus produces a wide range of secondary metabolites that are of biological and ecological importance Miadlikowska et al.
The lichen thallus is able to grow under a range of adverse conditions and some can survive for hundreds of years. Lichens are found in a wide range of habitats from the Arctic to Antarctic, including some species that can grow in aquatic and marine environments Webster and Weber Phylum Basidiomycota represents the second largest phylum of fungi, with nearly 30, described species.
Members of phylum Basidiomycota produce basidiospores on a typically club-shaped structure called a basidium Fig. Characteristic of the mycelium of many members of Basidiomycota is the presence of clamp connections Figs. Three main lineages are recognized in phylum Basidiomycota: subphyla Ustilaginomycotina, Pucciniomycotina, and Agaricomycotina Blackwell et al. Ustilaginomycotina and Pucciniomycotina are composed mostly of plant parasitic species, known as smut and rust fungi, respectively, characterized by a state that produces thick-walled teliospores Figs.
The most extensively studied members of Ustilaginomycotina are species of Tilletia and Ustilago. Ustilago maydis , which causes corn smut Fig. These structures eventually become filled with dark teliospores and are considered a delicacy in Mexico called "cuitlacoche. Subphylum Pucciniomycotina include the group of plant parasites called rust fungi. The rust fungi are remarkable in having as many as five distinct types of spores in a single life cycle spermatia, aeciospores, urediniospores, teliospores, and basidiospores Fig.
Rust fungi that produce all five spore states are macrocyclic , those that do not form uredinospores are demicyclic , and those that do not form urediniospores and aeciospores are microcyclic. Rust fungi may complete the life cycle on one host autoecious rusts or require two unrelated alternate hosts for completion of the life cycle heteroecious rusts.
The most widely cited example of a macrocyclic, heteroecious rust is Puccinia graminis black stem rust , which forms two spore states uredinia and telia on cultivated wheat Fig. The fifth state, the probasidium producing basidiospores, is formed upon germination of the teliospores Fig.
Subphylum Agaricomycotina, previously known as the Hymenomycetes, includes the morphologically diverse group of fungi that produce basidia in various types of fruiting bodies Fig. This group includes the fungi commonly known as mushrooms Fig. Many species are saprotrophic, utilizing dead plant material including woody substrates. Some of these saprotrophic species are cultivated for food, for example, the common button mushroom Agaricus bisporus , oyster mushrooms Pleurotus ostreatus , and shiitake Lentinula edodes.
Other members of this group are important ectomycorrhizal fungi, forming mutualistic associations with the roots of a wide range of trees. Some fruiting bodies produced by ectomycorrhizae are considered choice edibles, for example, chanterelles Cantharellus cibarius and other species , porcini Boletus edulis , and the American matsutake Tricholoma magnivelare Fig.
A few members of this group are economically important plant parasites, e. This is an ancient group of fungi, recognizable in the fossil record dating back at least million years. Some AM fungi also produce storage structures inside plant roots called vesicles. Endomycorrhizal fungi produce an extensive network of hyphae outside the roots extraradical hyphae. The extraradical hyphae act like an extension of the plant roots, increasing the plant's access to water and soil minerals, particularly phosphorous and nitrogen.
The fungus is also able to access phosphate not otherwise available to plants, for example from organic matter by production of acid phosphatases. Spores may be formed singly or in clusters, and the mycelium of AM fungi is coenocytic.
Sexual reproduction is not known to occur in this phylum. The feature that is shared by all members of this phylum is the formation of zoospores with one posteriorly directed, whiplash flagellum.
A few chytrids are economically important plant pathogens, e. As previously noted, the frog chytrid, Batrachochytrium dendrobatidis , has been implicated as a major factor in population declines of frogs and other amphibians around the world Berger et al. This phylum contains approximately identified species divided amongst two ecologically distinct classes, Zygomycetes and Trichomycetes White et al. The most commonly encountered Zygomycetes are members of orders Mortierellales and Mucorales.
Many members of these two orders are saprotrophs with rapidly growing, coenocytic mycelium. The sexual reproductive state is the zygospore Fig. Members of order Mucorales, commonly called mucoraceous fungi, are common in soil, dung, plant material, and other types of organic matter. Some mucoraceous fungi are plant or animal pathogens, and others are used in the production of Asian foods such as tempeh.
Species of Mucor and Rhizopu s Fig. Species of Pilobolus Figs. Other Zygomycetes are associated with animals. For example, some species of Rhizopus and Mucor cause zygomycosis in immunocompromised humans. Entomophthorales, as the name suggests, include parasites of insects and other animals. Members of class Trichomycetes live in the guts of insects, millipedes, and crustaceans, but cause little or no harm to their hosts.
Instead, fungi have to get their food from other sources, living or dead. Animals, like fungi, cannot make their own food but they can at least move to find the food they need. Fungi are very different from plants and animals, and there are so many kinds of fungi.
There are more different kinds of fungi in the forests of Aotearoa than different kinds of plants, and there are even more different kinds of insects and other animals.
All of these fungi, plants and animals live together in the forest and are linked together in many ways including in food webs. Instead, fungi grow as masses of narrow branched threads called hyphae. These hyphae have thin outer walls, and their food, water and oxygen need to move across the wall into the living fungal cell — a process called absorption. Any waste products, like CO 2 , leave the cell by crossing the thin wall in the other direction.
Hyphae can change their form from when they are feeding to when they become part of a mushroom, for example. A mushroom is made up of masses of specially arranged hyphae. Fungal hyphae can often be seen as white threads, about as narrow as spider silk, among dead leaves on the forest floor or under bark of rotting trees, or they can be grown in a laboratory on a kind of jelly-like food in a plastic Petri dish.
This and other Saccharomyces species are used for brewing beer. Figure 7. The life cycle of an ascomycete is characterized by the production of asci during the sexual phase. The haploid phase is the predominant phase of the life cycle. The Basidiomycota basidiomycetes are fungi that have basidia club-shaped structures that produce basidiospores spores produced through budding within fruiting bodies called basidiocarps Figure 8.
They are important as decomposers and as food. This group includes rusts, stinkhorns, puffballs, and mushrooms. Several species are of particular importance. Cryptococcus neoformans , a fungus commonly found as a yeast in the environment, can cause serious lung infections when inhaled by individuals with weakened immune systems.
The edible meadow mushroom, Agricus campestris , is a basidiomycete, as is the poisonous mushroom Amanita phalloides , known as the death cap. The deadly toxins produced by A. Figure 8. The life cycle of a basidiomycete alternates a haploid generation with a prolonged stage in which two nuclei dikaryon are present in the hyphae.
Finally, the Microsporidia are unicellular fungi that are obligate intracellular parasites. They lack mitochondria, peroxisomes, and centrioles, but their spores release a unique polar tubule that pierces the host cell membrane to allow the fungus to gain entry into the cell. A number of microsporidia are human pathogens, and infections with microsporidia are called microsporidiosis. One pathogenic species is Enterocystozoan bieneusi , which can cause symptoms such as diarrhea, cholecystitis inflammation of the gall bladder , and in rare cases, respiratory illness.
Histoplasma capsulatum Aspergillus niger Basidiomycota Basidia. Amanita phalloides Cryptococcus neoformans Amanita phalloides Microsporidia Lack mitochondria, peroxisomes, and centrioles. Spores produce a polar tube Enterocystozoan bieneusi Enterocystozoan bieneusi Microsporidia unidentified Zygomycota Mainly saprophytes.
Zygospores Rhizopus stolonifera Mucor spp. Rhizopus sp. Think about It Which group of fungi appears to be associated with the greatest number of human diseases? Eukaryotic Pathogens in Eukaryotic Hosts When we think about antimicrobial medications, antibiotics such as penicillin often come to mind. Penicillin and related antibiotics interfere with the synthesis of peptidoglycan cell walls, which effectively targets bacterial cells. These antibiotics are useful because humans like all eukaryotes do not have peptidoglycan cell walls.
Developing medications that are effective against eukaryotic cells but not harmful to human cells is more difficult. Despite huge morphological differences, the cells of humans, fungi, and protists are similar in terms of their ribosomes, cytoskeletons, and cell membranes. As a result, it is more challenging to develop medications that target protozoans and fungi in the same way that antibiotics target prokaryotes. Fungicides have relatively limited modes of action. Because fungi have ergosterols instead of cholesterol in their cell membranes, the different enzymes involved in sterol production can be a target of some medications.
The azole and morpholine fungicides interfere with the synthesis of membrane sterols. These are used widely in agriculture fenpropimorph and clinically e. Some antifungal medications target the chitin cell walls of fungi. Despite the success of these compounds in targeting fungi, antifungal medications for systemic infections still tend to have more toxic side effects than antibiotics for bacteria.
Anthony is relieved the ringworm is not an actual worm, but wants to know what it really is. The physician explains that ringworm is a fungus. He tells Anthony that he will not see mushrooms popping out of his skin, because this fungus is more like the invisible part of a mushroom that hides in the soil. They physician reassures Anthony that they are going to get the fungus out of him too.
Macroscopic filamentous fungi also grow by producing a mycelium below ground. They differ from moulds because they produce visible fruiting bodies commonly known as mushrooms or toadstools that hold the spores. The fruiting body is made up of tightly packed hyphae which divide to produce the different parts of the fungal structure, for example the cap and the stem. Gills underneath the cap are covered with spores and a 10 cm diameter cap can produce up to million spores per hour.
Yeasts are small, lemon-shaped single cells that are about the same size as red blood cells. They multiply by budding a daughter cell off from the original parent cell. Scars can be seen on the surface of the yeast cell where buds have broken off. Yeasts such as Saccharomyces play an important role in the production of bread and in brewing.
Yeasts are also one of the most widely used model organisms for genetic studies, for example in cancer research. Other species of yeast such as Candida are opportunistic pathogens and cause infections in individuals who do not have a healthy immune system.
0コメント