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For the fictional character, see Fungus the Bogeyman. For the music genre, see Fungi (music).
| Fungi Fossil range: Early Silurian - Recent | ||||||
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 Clockwise from top left: Amanita muscaria, a basidiomycete; Sarcoscypha coccinea, an ascomycete; black bread mold, a zygomycete; a chytrid; a Penicillium conidiophore. | ||||||
| Scientific classification | ||||||
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| Subkingdoms/Phyla | ||||||
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Dikarya (inc. Deuteromycota) |
A fungus (pronounced /ˈfʌŋgəs/) is any eukaryotic organism that is a member of the kingdom Fungi (pronounced /ˈfʌndʒaɪ/).These are the pronunciations listed first in most dictionaries. See, for example, the Merriam-Webster Online entry Alternative pronunciations for fungi include /ˈfʌŋgaɪ/, /ˈfʌndʒi/, and /ˈfʌŋgi/. Funguses (/ˈfʌŋgəsəz/) is an alternative plural form. The fungi are heterotrophic organisms characterized by a chitinous cell wall, and in the majority of species, filamentous growth as multicellular hyphae forming a mycelium; some fungal species also grow as single cells. Sexual and asexual reproduction is commonly via spores, often produced on specialized structures or in fruiting bodies. Some fungal species have lost the ability to form specialized reproductive structures, and propagate solely by vegetative growth. Yeasts, molds, and mushrooms are examples of fungi. The fungi are a monophyletic group that is phylogenetically clearly distinct from the morphologically similar slime molds (myxomycetes) and water molds (oomycetes). The fungi are more closely related to animals than plants, yet the discipline of biology devoted to the study of fungi, known as mycology, often falls under a branch of botany.
Occurring worldwide, most fungi are largely invisible to the naked eye, living for the most part in soil, dead matter and as symbionts of plants, animals, or other fungi. They perform an essential role in all ecosystems in decomposing matter and are indispensable in nutrient cycling and exchange. Some fungi become noticeable when fruiting, either as mushrooms or molds. Many fungal species have long been used as a direct source of food, such as mushrooms and truffles and in fermentation of various food products, such as wine, beer, and soy sauce. More recently, fungi are being used as sources for antibiotics and various enzymes, such as cellulases, pectinases, and proteases, important for industrial use or as active ingredients of detergents. Many fungi produce bioactive compounds, such as alkaloids and polyketides that are toxic to animals including humans and are, therefore, called mycotoxins. Some fungi are used recreationally or in traditional ceremonies as a source of psychotropic compounds. Several species of the fungi are significant pathogens of humans and other animals, and losses due to diseases of crops (e.g., rice blast disease) or food spoilage caused by fungi can have a large impact on human food supply and local economies.
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The English word fungus is directly adopted from the Latin fungus, meaning "mushroom", used in Horace and Pliny.Simpson, D.P. (1979). Cassell\'s Latin Dictionary, 5, London: Cassell Ltd., 883. ISBN 0-304-52257-0. This in turn is derived from the Greek word sphongos/σφογγος ("sponge"), referring to the macroscopic structures and morphology of some mushrooms and molds and also used in other languages (e.g., the German Schwamm ("sponge") or Schwammerl for some types of mushroom).
Fungi have a worldwide distribution, and grow in a wide range of habitats, including deserts. Most fungi grow in terrestrial environments, but several species occur only in aquatic habitats. Fungi along with bacteria are the primary decomposers of organic matter in most if not all terrestrial ecosystems worldwide. Based on observations of the ratio of the number of fungal species to the number of plant species in some environments, the fungal kingdom has been estimated to contain about 1.5 million species. Hawksworth DL (2006). "The fungal dimension of biodiversity: magnitude, significance, and conservation". Mycol. Res. 95: 641–655. Around 70,000 fungal species have been formally described by taxonomists, but the true dimension of fungal diversity is still unknown. Mueller GM, Schmit JP (2006). "Fungal biodiversity: what do we know? What can we predict?". Biodivers Conserv 16: 1–5. Most fungi grow as thread-like filaments called hyphae, which form a mycelium, while others grow as single cells. Alexopoulos CJ, Mims CW, Blackwell M (1996). Introductory Mycology. John Wiley and Sons. ISBN 0471522295. Meredith Blackwell; Rytas Vilgalys, and John W. Taylor (2005-02-14). Eumycota: mushrooms, sac fungi, yeast, molds, rusts, smuts, etc. (English). Retrieved on 2007-04-06. Until recently many fungal species were described based mainly on morphological characteristics, such as the size and shape of spores or fruiting structures, and biological species concepts; the application of molecular tools, such as DNA sequencing, to study fungal diversity has greatly enhanced the resolution and added robustness to estimates of diversity within various taxonomic groups.Hibbett, D.S., et al. (2007). "A higher level phylogenetic classification of the Fungi". Mycol. Res. 111 (5): 509-547. doi:doi:10.1016/j.mycres.2007.03.004.
Sacharomyces cerevisiae cells in DIC microscopy.
Human use of fungi for food preparation or preservation and other purposes is extensive and has a long history: yeasts are required for fermentation of beer, wine Strains of wine yeast and bread, some other fungal species are used in the production of soy sauce and tempeh. Mushroom farming and mushroom gathering are large industries in many countries. Many fungi are producers of antibiotics, including β-lactam antibiotics such as penicillin and cephalosporin.Demain AL. (1991). "Production of beta-lactam antibiotics and its regulation.". Proc Natl Sci Counc Repub China B. 15: 251-265. PMID 1815263. Widespread use of these antibiotics for the treatment of bacterial diseases, such as tuberculosis, syphilis, leprosy, and many others began in the early 20th century and continues to play a major part in anti-bacterial chemotherapy. The study of the historical uses and sociological impact of fungi is known as ethnomycology.
Baker\'s yeast or Saccharomyces cerevisiae, a single-cell fungus, is used in the baking of bread and other wheat-based products, such as pizza and dumplings.Kulp, Karel (2000). Handbook of Cereal Science and Technology. CRC Press. ISBN 0824782941. Several yeast species of the genus Saccharomyces are also used in the production of alcoholic beverages through fermentation.Piskur J, Rozpedowska E, Polakova S, Merico A, Compagno C. (2006). "How did Saccharomyces evolve to become a good brewer?". Trends Genet. 22: 183-186. PMID 16499989. Mycelial fungi, such as the shoyu koji mold (Aspergillus oryzae), are used in the brewing of Shoyu (soy sauce) and preparation of tempeh.Kitamoto N, Yoshino S, Ohmiya K, Tsukagoshi N. (1999). "Sequence analysis, overexpression, and antisense inhibition of a beta-xylosidase gene, xylA, from Aspergillus oryzae KBN616.". Appl. Env. Microbiol. 65: 20-24. PMID 9872754. Quorn is a high-protein product made from the mold, Fusarium venenatum, and is used in vegetarian cooking.
Fungi are also used extensively to produce industrial chemicals like lactic acid, antibiotics and even to make stonewashed jeans.Trichoderma spp., including T. harzianum, T. viride, T. koningii, T. hamatum and other spp. Deuteromycetes, Moniliales (asexual classification system). Biological Control: A Guide to Natural Enemies in North America. Retrieved on 2007-07-10. Several fungal species are ingested for their psychedelic properties, both recreationally and religiously (see main article, Psilocybin mushrooms).
Many fungi produce compounds with biological activity. Several of these compounds are toxic and are therefore called mycotoxins, referring to their fungal origin and toxic activity. Of particular relevance to humans are those mycotoxins that are produced by moulds causing food spoilage and poisonous mushrooms (see below). Particularly infamous are the aflatoxins, which are insidious liver toxins and highly carcinogenic metabolites produced by Aspergillus species often growing in or on grains and nuts consumed by humans, and the lethal amatoxins produced by mushrooms of the genus Amanita. Other notable mycotoxins include ochratoxins, patulin, ergot alkaloids, and trichothecenes and fumonisins, all of which have significant impact on human food supplies or animal livestock. van Egmond HP, Schothorst RC, Jonker MA (2007). "Regulations relating to mycotoxins in food: perspectives in a global and European context". Anal Bioanal Chem. 389: 147-157. PMID 17508207.
Mycotoxins belong to the group of secondary metabolites (or natural products). Originally, this group of compounds had been thought to be mere byproducts of primary metabolism, hence the name "secondary" metabolites. However, recent research has shown the existence of biochemical pathways solely for the purpose of producing mycotoxins and other natural products in fungi. Keller NP, Turner G, Bennett JW (2005). "Fungal secondary metabolism - from biochemistry to genomics". Nat Rev Microbiol. 3: 937-497. PMID 16322742. Mycotoxins provide a number of fitness benefits to the fungi that produce them in terms of physiological adaptation, competition with other microbes and fungi, and protection from fungivory. Demain AL, Fang A (2000). "The natural functions of secondary metabolites". Adv Biochem Eng Biotechnol. 69: 1-39. PMID 11036689. Rohlfs M, Albert M, Keller NP, Kempken F (2007). "Secondary chemicals protect mould from fungivory". Biol Lett. 3: 523-525. PMID 17686752. These fitness benefits and the existence of dedicated biosynthetic pathways for mycotoxin production suggest that the mycotoxins are important for fungal persistence and survival.
Asian mushrooms, clockwise from left, enokitake, buna-shimeji, bunapi-shimeji, king oyster mushroom and shiitake.
Black Périgord Truffle (Tuber melanosporum), cut in half.
Stilton cheese veined with Penicillium roqueforti.
Some of the best known types of fungi are the edible and the poisonous mushrooms. Many species are commercially raised, but others must be harvested from the wild. Agaricus bisporus, sold as button mushrooms when small or Portobello mushrooms when larger, are the most commonly eaten species, used in salads, soups, and many other dishes. Many Asian fungi are commercially grown and have gained in popularity in the West. They are often available fresh in grocery stores and markets, including straw mushrooms (Volvariella volvacea), oyster mushrooms (Pleurotus ostreatus), shiitakes (Lentinula edodes), and enokitake (Flammulina spp.).
There are many more mushroom species that are harvested from the wild for personal consumption or commercial sale. Milk mushrooms, morels, chanterelles, truffles, black trumpets, and porcini mushrooms (Boletus edulis) (also known as king boletes) all demand a high price on the market. They are often used in gourmet dishes.
For certain types of cheeses, it is also a common practice to inoculate milk curds with fungal spores to foment the growth of specific species of mold that impart a unique flavor and texture to the cheese. This accounts for the blue colour in cheeses such as Stilton or Roquefort which is created using Penicillium roqueforti spores.Questions & Answers - Mold on Cheese whatscookingamerica.net. Retrieved 2007-04-06. Molds used in cheese production are usually non-toxic and are thus safe for human consumption; however, mycotoxins (e.g., aflatoxins, roquefortine C, patulin, or others) may accumulate due to fungal spoilage during cheese ripening or storage.Erdogan A, Gurses M, Sert S. (2004). "Isolation of moulds capable of producing mycotoxins from blue mouldy Tulum cheeses produced in Turkey.". Int J Food Microbiol. 85: 83-85. PMID 12810273.
Many mushroom species are toxic to humans, with toxicities ranging from slight digestive problems or allergic reactions as well as hallucinations to severe organ failures and death. Some of the most deadly mushrooms belong to the genera Inocybe, Cortinarius, and most infamously, Amanita, which includes the destroying angel (A. virosa) and the death cap (A. phalloides), the most common cause of deadly mushroom poisoning. On the Trail of the Death Cap Mushroom Richard Harris, www.npr.org, 2007-02-08. Retrieved 2007-04-06. The false morel (Gyromitra esculenta) is considered a delicacy by some when cooked yet can be deadly when raw. Tricholoma equestre is one which was considered edible for centuries yet recently responsible for a series of serious poisonings in France.
Fly agaric mushrooms (A. muscaria) also cause occasional poisonings, mostly as a result of ingestion for use as a recreational drug for its hallucinogenic properties. Historically Fly agaric was used by Celtic Druids in Northern Europe and the Koryak people of north-eastern Siberia for religious or shamanic purposes.Mythology and Folklore of Fly Agaric Paul Kendall, Trees for Life. Retrieved 2007-04-06. It is difficult to identify a safe mushroom without proper training and knowledge, thus it is often advised to assume that a mushroom in the wild is poisonous and not to consume it.
In agricultural settings, fungi that actively compete for nutrients and space with, and eventually prevail over, pathogenic microorganisms, such as bacteria or other fungi, via the competitive exclusion principle,López-Gómez J, Molina-Meyer M (2006). "The competitive exclusion principle versus biodiversity through competitive segregation and further adaptation to spatial heterogeneities". Theor Popul Biol. 69: 94-109. PMID 16223517. or are parasites of these pathogens, may be beneficial agents for human use. For example, some fungi may be used to suppress growth or eliminate harmful plant pathogens, such as insects, mites, weeds, nematodes and other fungi that cause diseases of important crop plants.Setting the Stage To Screen Biocontrol Fungi Hank Becker, July 1998. Retrieved 2007-04-06. This has generated strong interest in the use and practical application of these fungi for the biological control of these agricultural pests. Entomopathogenic fungi can be used as biopesticides, as they actively kill insects.WHEY-BASED FUNGAL MICROFACTORY TECHNOLOGY FOR ENHANCED BIOLOGICAL PEST MANAGEMENT USING FUNGI Todd. S. Keiller, Technology Transfer, University of Vermont. Retrieved 2007-04-06. Examples of fungi that have been used as bioinsecticides are Beauveria bassiana, Metarhizium anisopliae, Hirsutella spp, Paecilomyces fumosoroseus, and Verticillium lecanii.Deshpande MV. (1999). "Mycopesticide production by fermentation: potential and challenges.". Crit Rev Microbiol. 25: 229-243. PMID 10524330. Thomas MB, Read AF. (2007). "Can fungal biopesticides control malaria?". Nat Rev Microbiol. 5: 377-383. PMID 17426726. Endophytic fungi of grasses of the genus Neotyphodium, such as N. coenophialum produce alkaloids that are toxic to a range of invertebrate and vertebrate herbivores. These alkaloids protect the infected grass plants from herbivory, but some endophyte alkaloids can cause poisoning of grazing animals, such as cattle and sheep. Bush LP, Wilkinson HH, Schardl CL. (1997). "Bioprotective Alkaloids of Grass-Fungal Endophyte Symbioses". Plant Physiol. 114: 1-7. PMID 12223685. Infection of grass cultivars of turf or forage grasses with isolates of the grass endophytes that produce only specific alkaloids to improve grass hardiness and resistance to herbivores such as insects, while being non-toxic to livestock, is being used in grass breeding programs.Bouton JH, Latch GCM, Hill NS, Hoveland CS, McCannc MA, Watson RH, Parish JA, Hawkins LL, Thompson FN (2002). "Use of nonergot alkaloid-producing endophytes for alleviating tall fescue toxicosis in sheep.". Agron. J. 94: 567-574. http://agron.scijournals.org/cgi/content/full/94/3/567.
Polypores growing on a tree in Borneo
Although often inconspicuous, fungi occur in every environment on Earth and play very important roles in most ecosystems. Along with bacteria, fungi are the major decomposers in most terrestrial (and some aquatic) ecosystems, and therefore play a critical role in biogeochemical cycles and in many food webs. As decomposers, they play an indispensable role in nutrient cycling, especially as saprotrophs and symbionts, degrading organic matter to inorganic molecules, which can then re-enter anabolic metabolic pathways in plants or other organisms.Lindahl BD, Ihrmark K, Boberg J, Trumbore SE, Högberg P, Stenlid J, Finlay RD (2007). "Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forest". New Phytol. 173: 611-620. PMID 17244056. Barea JM, Pozo MJ, Azcón R, Azcón-Aguilar C (2005). "Microbial co-operation in the rhizosphere". J. Exp. Bot. 56: 1761-1778. PMID 15911555.
Many fungi have important symbiotic relationships with organisms from most if not all Kingdoms.Aanen DK. (2006). "As you reap, so shall you sow: coupling of harvesting and inoculating stabilizes the mutualism between termites and fungi.". Biol Lett. 2: 209-212. PMID 17148364. Nikoh N, Fukatsu T. (2000). "Interkingdom host jumping underground: phylogenetic analysis of entomoparasitic fungi of the genus Cordyceps.". Mol Biol Evol. 17: 2629-2638. PMID 10742053. Perotto S, Bonfante P. (1997). "Bacterial associations with mycorrhizal fungi: close and distant friends in the rhizosphere.". Trends Microbiol. 5: 496-501. PMID 9447662. These interactions can be mutualistic or antagonistic in nature, or in case of commensal fungi are of no apparent benefit or detriment to the host. Arnold AE, Mejía LC, Kyllo D, Rojas EI, Maynard Z, Robbins N, Herre EA. (2003). "Fungal endophytes limit pathogen damage in a tropical tree.". Proc. Natl. Acad. Sci. USA 100: 15649-15654. PMID 14671327. Paszkowski U. (2006). "Mutualism and parasitism: the yin and yang of plant symbioses.". Curr Opin Plant Biol. 9: 364-370. PMID 16713732. Hube B. (2004). "From commensal to pathogen: stage- and tissue-specific gene expression of Candida albicans.". Curr Opin Microbiol. 7: 336-341. PMID 15288621.
Mycorrhizal symbiosis between plants and fungi is one of the most well-known plant-fungus associations and is of significant importance for plant growth and persistence in many ecosystems; over 90% of all plant species engage in some kind of mycorrhizal relationship with fungi and are dependent upon this relationship for survival.Volk, Tom. Tom Volk\'s Fungi FAQ. Retrieved on 2006-09-21.Wong, George. Symbiosis: Mycorrhizae and Lichens. Retrieved on 2006-09-21. Knowledge of nitrogen transfer between plants and beneficial fungi expands southwestfarmpress.com. 2005-06-10 Retrieved 2007-04-06. The mycorrhizal symbiosis is ancient, dating to at least 400 million years ago.Remy W, Taylor TN, Hass H, Kerp H (1994). "4-hundred million year old vesicular-arbuscular mycorrhizae.". Proc. Natl. Acad. Sci 91: 11841-11843. PMID 11607500. It often increases the plant\'s uptake of inorganic compounds, such as nitrate and phosphate from soils having low concentrations of these key plant nutrients.van der Heijden MG, Streitwolf-Engel R, Riedl R, Siegrist S, Neudecker A, Ineichen K, Boller T, Wiemken A, Sanders IR (2006). "The mycorrhizal contribution to plant productivity, plant nutrition and soil structure in experimental grassland". New Phytol. 172: 739-752. PMID 17096799. In some mycorrhizal associations, the fungal partners may mediate plant-to-plant transfer of carbohydrates and other nutrients. Such mycorrhizal communities are called "common mycorrhizal networks". Selosse MA, Richard F, He X, Simard SW (2006). "Mycorrhizal networks: des liaisons dangereuses?". Trends Ecol Evol. 21: 621-628. PMID 16843567.
Lichens are formed by a symbiotic relationship between algae or cyanobacteria (referred to in lichens as "photobionts") and fungi (mostly various species of ascomycetes and a few basidiomycetes), in which individual photobiont cells are embedded in a tissue formed by the fungus.Brodo, Irwin M.; Sylvia Duran Sharnoff (2001). Lichens of North America. Yale University Press. ISBN 0300082495. As in mycorrhizas, the photobiont provides sugars and other carbohydrates, while the fungus provides minerals and water. The functions of both symbiotic organisms are so closely intertwined that they function almost as a single organism.
Many insects also engage in mutualistic relationships with various types of fungi. Several groups of ants cultivate fungi in the order Agaricales as their primary food source, while ambrosia beetles cultivate various species of fungi in the bark of trees that they infest.Fungi and Insect Symbiosis www.botany.hawaii.edu. Retrieved 2007-04-06. Termites on the African Savannah are also known to cultivate fungi.Pascal Jouquet, Virginie Tavernier, Luc Abbadie and Michel Lepage. Nests of subterranean fungus-growing termites (Isoptera, Macrotermitinae) as nutrient patches for grasses in savannah ecosystems. African Journal of Ecology. 2005. Vol 43, 191–196
However, many fungi are parasites on plants, animals (including humans), and other fungi. Serious fungal pathogens of many cultivated plants causing extensive damage and losses to agriculture and forestry include the rice blast fungus Magnaporthe oryzae,Talbot NJ (2003). "On the trail of a cereal killer: Exploring the biology of Magnaporthe grisea.". Annu Rev Microbiol. 57: 177-202. PMID 14527276. tree pathogens such as Ophiostoma ulmi and Ophiostoma novo-ulmi causing Dutch elm disease,Paoletti M, Buck KW, Brasier CM. (2006). "Selective acquisition of novel mating type and vegetative incompatibility genes via interspecies gene transfer in the globally invading eukaryote Ophiostoma novo-ulmi.". Mol Ecol. 15: 249-262. PMID 16367844. and Cryphonectria parasitica responsible for chestnut blight, Gryzenhout M, Wingfield BD, Wingfield MJ. (2006). "New taxonomic concepts for the important forest pathogen Cryphonectria parasitica and related fungi.". FEMS Microbiol Lett. 258: 161-172. PMID 16640568. and plant-pathogenic fungi in the genera Fusarium, Ustilago, Alternaria, and Cochliobolus; fungi with the potential to cause serious human diseases, especially in persons with immuno-deficiencies, are in the genera Aspergillus, Candida, Cryptoccocus,Nielsen K, Heitman J. (2007). "Sex and virulence of human pathogenic fungi.". Adv Genet. 57: 143-173. PMID 17352904. Brakhage AA (2005). "Systemic fungal infections caused by Aspergillus species: epidemiology, infection process and virulence determinants.". Curr. Drug Targets 6: 875-886. PMID 16375671. Histoplasma,Kauffman CA. (2007). "Histoplasmosis: a clinical and laboratory update". Clin Microbiol Rev. 20: 115-132. PMID 17223625. and Pneumocystis. Cushion MT, Smulian AG, Slaven BE, Sesterhenn T, Arnold J, Staben C, Porollo A, Adamczak R, Meller J. (2007). "Transcriptome of Pneumocystis carinii during Fulminate Infection: Carbohydrate Metabolism and the Concept of a Compatible Parasite.". PLoS ONE 2: e423. PMID 17487271. Several pathogenic fungi are also responsible for relatively minor human diseases, such as athlete’s foot and ringworm. Some fungi are predators of nematodes, which they capture using an array of devices such as constricting rings or adhesive nets.ILLUSTRATIONS for Predatory Fungi, wood Decay and the Carbon Cycle www.uoguelph.ca. Retrieved 2007-04-06.
Growth of fungi as hyphae on or in solid substrates or single cells in aquatic environments is adapted to efficient extraction of nutrients from these environments, because these growth forms have high surface area to volume ratios. These adaptations in morphology are complemented by hydrolytic enzymes secreted into the environment for digestion of large organic molecules, such as polysaccharides, proteins, lipids, and other organic substrates into smaller molecules. Pereira JL, Noronha EF, Miller RN, Franco OL. (2007). "Novel insights in the use of hydrolytic enzymes secreted by fungi with biotechnological potential.". Lett Appl Microbiol. 44: 573-581. PMID 17576216. Schaller M, Borelli C, Korting HC, Hube B. (2007). "Hydrolytic enzymes as virulence factors of Candida albicans.". Mycoses 48: 365-377. PMID 16262871. Farrar JF (1985). "Carbohydrate metabolism in biotrophic plant pathogens.". Microbiol Sci. 2: 314-317. PMID 3939987. These molecules are then absorbed as nutrients into the fungal cells.
Traditionally, the fungi are considered heterotrophs, organisms that rely solely on carbon fixed by other organisms for metabolism. Fungi have evolved a remarkable metabolic versatility that allows many of them to use a large variety of organic substrates for growth, including simple compounds as nitrate, ammonia, acetate, or ethanol.Marzluf GA (1981). "Regulation of nitrogen metabolism and gene expression in fungi". Microbiol Rev. 45: 437-461. PMID 6117784. Heynes MJ (1994). "Regulatory circuits of the amdS gene of Aspergillus nidulans". Antonie Van Leeuwenhoek. 65: 179-782. PMID 7847883. Recent research raises the possibility that some fungi utilize the pigment melanin to extract energy from ionizing radiation, such as gamma radiation for "radiotrophic" growth. Dadachova E, Bryan RA, Huang X, Moadel T, Schweitzer AD, Aisen P, Nosanchuk JD, Casadevall A. (2007). "Ionizing radiation changes the electronic properties of melanin and enhances the growth of melanized fungi". PLoS ONE 2: e457. PMID 17520016. It has been proposed that this process might bear some similarity to photosynthesis in plants, but detailed biochemical data supporting the existence of this hypothetical pathway are presently lacking.
Mold covering a decaying peach over a period of six days. The frames were taken approximately 12 hours apart.
Though fungi are part of the opisthokont clade, all phyla except for the chytrids have lost their posterior flagella.The Protistan Origins of Animals and Fungi Emma T. Steenkamp, Jane Wright and Sandra L. Baldauf. Molecular Biology and Evolution 2006 23(1):93-106; doi:10.1093/molbev/msj011. Retrieved 2007-04-06. Fungi are unusual among the eukaryotes in having a cell wall that, besides glucans (e.g., β-1,3-glucan) and other typical components, contains the biopolymer chitin.Stevens DA, Ichinomiya M, Koshi Y, Horiuchi H. (2006). "Escape of Candida from caspofungin inhibition at concentrations above the MIC (paradoxical effect) accomplished by increased cell wall chitin; evidence for beta-1,6-glucan synthesis inhibition by caspofungin.". Antimicrob Agents Chemother. 50: 3160-3161.. PMID 16940118.
Many fungi grow as thread-like filamentous microscopic structures called hyphae, and an assemblage of intertwined and interconnected hyphae is called a mycelium. Alexopoulos CJ, Mims CW, Blackwell M (1996). Introductory Mycology. John Wiley and Sons. ISBN 0471522295. Hyphae can be septate, i.e., divided into hyphal compartments separated by a septum, each compartment containing one or more nuclei or can be coenocytic, i.e., lacking hyphal compartmentalization. However, septa have pores, such as the doliporus in the basidiomycetes that allow cytoplasm, organelles, and sometimes nuclei to pass through. Coenocytic hyphae are essentially multinucleate supercells.Chang, Shu-ting; Philip G. Miles (2004). Mushrooms: Cultivation, Nutritional Value, Medicinal Effect and Environmental Impact. CRC Press. ISBN 0849310431. In some cases, fungi have developed specialized structures for nutrient uptake from living hosts; examples include haustoria in plant-parasitic fungi of nearly all divisions, and arbuscules of several mycorrhizal fungi,“Fungal Biology” at The University of Sydney Retrieved on 26 June 2007 which penetrate into the host cells for nutrient uptake by the fungus.
Fungal mycelia can become visible macroscopically, for example, as concentric rings on various surfaces, such as damp walls, and on other substrates, such as spoilt food (see figure), and are commonly and generically called mould (American spelling, mold); fungal mycelia grown on solid agar media in laboratory petri dishes are usually referred to as colonies, with many species exhibiting characteristic macroscopic growth morphologies and colours, due to spores or pigmentation.
Specialized fungal structures important in sexual reproduction are the apothecia, perithecia, and cleistothecia in the ascomycetes, and the fruiting bodies of the basidiomycetes, and a few ascomycetes. These reproductive structures can sometimes grow very large, and are well known as mushrooms.
Fungal hyphae are specifically adapted to growth on solid surfaces and within substrates, and can exert astoundingly large penetrative mechanical forces. The plant pathogen, Magnaporthe grisea, forms a structure called an appressorium specifically designed for penetration of plant tissues, and the pressure generated by the appressorium, which is directed against the plant epidermis can exceed 8 MPa (80 bars). Howard RJ, Ferrari MA, Roach DH, Money NP (1991). "Penetration of hard substrates by a fungus employing enormous turgor pressures". Proc Natl Acad Sci U S A. 88: 11281-11284. PMID 1837147. The generation of these mechanical pressures is the result of an interplay between physiological processes to increase intracellular turgor by production of osmolytes such as glycerol, and the morphology of the appressorium. Wang ZY, Jenkinson JM, Holcombe LJ, Soanes DM, Veneault-Fourrey C, Bhambra GK, Talbot NJ (2005). "The molecular biology of appressorium turgor generation by the rice blast fungus Magnaporthe grisea". Biochem Soc Trans. 33: 384-388. PMID 15787612.
Fungi on a fence post near Orosí, Costa Rica.
Reproduction of fungi is complex, reflecting the heterogeneity in lifestyles and genetic make up within this group of organisms. Many fungi reproduce both sexually or asexually, depending on conditions in the environment. These conditions trigger genetically determined developmental programs leading to the expression of specialized structures for sexual or asexual reproduction. These structures aid both reproduction and efficient dissemination of spores or spore-containing propagules.
Asexual reproduction via vegetative spores or through mycelial fragmentation is common in many fungal species and allows more rapid dispersal than sexual reproduction. In the case of the "Fungi imperfecti" or Deuteromycota, which lack a sexual cycle, it is the only means of propagation. Asexual spores, upon germination, may found a population that is clonal to the population from which the spore originated, and thus colonize new environments.
Sexual reproduction with meiosis exists in all fungal phyla, except the Deuteromycota. It differs in many aspects from sexual reproduction in animals or plants. Many differences also exist between fungal groups and have been used to discriminate fungal clades and species based on morphological differences in sexual structures and reproductive strategies. Experimental crosses between fungal isolates can also be used to identify species based on biological species concepts. The major fungal clades have initially been delineated based on the morphology of their sexual structures and spores; for example, the spore-containing structures, asci and basidia, can be used in the identification of ascomycetes and basidiomycetes, respectively. Many fungal species have elaborate vegetative incompatibility systems that allow mating only between individuals of opposite mating type, while others can mate and sexually reproduce with any other individual or itself. Species of the former mating system are called heterothallic, and of the latter homothallic. Metzenberg RL, Glass NL. (1990). "Mating type and mating strategies in Neurospora.". Bioessays 12: 53-59. PMID 2140508.
Most fungi have both a haploid and diploid stage in their life cycles. In all sexually reproducing fungi, compatible individuals combine by cell fusion of vegetative hyphae by anastomosis, required for the initiation of the sexual cycle. Ascomycetes and basidiomycetes go through a dikaryotic stage, in which the nuclei inherited from the two parents do not fuse immediately after cell fusion, but remain separate in the hyphal cells (see heterokaryosis).
In ascomycetes, dikaryotic hyphae of the hymenium form a characteristic hook at the hyphal septum. During cell division formation of the hook ensures proper distribution of the newly divided nuclei into the apical and basal hyphal compartments. An ascus (plural asci) is then formed, in which karyogamy (nuclear fusion) occurs. These asci are embedded in an ascocarp, or fruiting body, of the fungus. Karyogamy in the asci is followed immediately by meiosis and the production of ascospores. The ascospores are disseminated and germinate and may form a new haploid mycelium.
Sexual reproduction in basidiomycetes is similar to that of the ascomycetes. Compatible haploid hyphae fuse to produce a dikaryotic mycelium. However, the dikaryotic phase is more extensive in the basidiomycetes, in many cases also present in the vegetatively growing mycelium. A specialized anatomical structure, called a clamp connection, is formed at each hyphal septum. As with the structurally similar hook in the ascomycetes, formation of the clamp connection in the basidiomycetes is required for controlled transfer of nuclei during cell division, to maintain the dikaryotic stage with two genetically different nuclei in each hyphal compartment. A basidiocarp is formed in which club-like structures known as basidia generate haploid basidiospores after karyogamy and meiosis.Reproduction of fungi MicrobiologyBytes, 2007-01-18. Retrieved 2007-04-06. The most commonly known basidiocarps are mushrooms, but they may also take many other forms (see Morphology section).
In zygomycetes, haploid hyphae of two individuals fuse, forming a zygote, which develops into a zygospore. When the zygospore germinates, it quickly undergoes meiosis, generating new haploid hyphae, which in turn may form asexual sporangiospores. These sporangiospores are means of rapid dispersal of the fungus and germinate into new genetically identical haploid fungal colonies, able to mate and undergo another sexual cycle followed by the generation of new zygospores, thus completing the lifecycle.
Both asexual and sexual spores or sporangiospores of many fungal species are actively dispersed by forcible ejection from their reproductive structures. This ejection ensures exit of the spores from the reproductive structures as well as travelling through the air over long distances. Many fungi thereby possess specialized mechanical and physiological mechanisms as well as spore-surface structures, such as hydrophobins, for spore ejection. These mechanisms include, for example, forcible discharge of ascospores enabled by the structure of the ascus and accumulation of osmolytes in the fluids of the ascus that lead to explosive discharge of the ascospores into the air. Trail F. (2007). "Fungal cannons: explosive spore discharge in the Ascomycota". FEMS Microbiol Lett. 276: 12-18. PMID 17784861. The forcible discharge of single spores termed ballistospores involves formation of a small drop of water (Buller\'s drop), which upon contact with the spore leads to its projectile release with an initial acceleration of more than 10,000
