Fungi

mold

A rapidly growing, asexually reproducing fungus. The mycelia of these fungi grow as saprobes or parasites on a variety of substrates. Early in life, a mold, a term that applies properly only to the asexual stage, produces asexual spores. Later the same fungus may reproduce sexually, producing zygosporangia, ascocarps, or basidiocarps.

Some fungi are pathogens

About 30% of the 100,000 known species of fungi are parasites, mostly on or in plants. Invasive ascomycetes have had drastic effects on forest trees, such as American elms and American chestnut, in the northeastern United States. Other fungi, such as rusts and ergots, infect grain crops, causing tremendous economic losses each year.

Lichens

Actually symbiotic association of photosynthetic microorganisms in a mesh of fungal hyphae. Photosynthetic partners are usually unicellular or filamentous green algae or cyanobacteria. Over 25,000 species have been described. Lichen in extreme environments, are the the only land "plants" that are tough enough to grow in Antartica. Some lichens in an experiment survived a bath in liquid nitrogen at minus 195 degrees. Some lichens have been found only about 400km from the South Pole. Lichens even grow on the summit of Mt Everest. Lichens may be the world's oldest organisms. One giant lichen in Michigan is thought to be over 10,000 years old. Lichen in the Arctic are more than 8,300 years old. Some scientists think they are functionally immortal-they will never die of old age ( but can be killed, of course). The fungal hyphae provides most of the lichens's mass and gives it its overall shape and structure. The algal component usually occupies an inner layer below the lichen surface. Lichen are not purely mutualistic, if haustoria form the fungal partner were to appear within the photosynthetic partner of a lichen, and if the growth rate of the photosynthetic partner consequently slowed substantially.

plasmogamy

Before karyogamy, the cytoplasmic fusion by the two parents.

Basidiomycetes

Elaborate fruiting body called baisidiocarp. Club fungi have long-lived dikaryotic mycelia. Approximately 25,000 fungi, including mushrooms, shelf fungi, puffballs, and rusts are classified in phylum Basidiomycota. The life cycle of a club fungus usually includes a long-lived dikaryotic mycelium.

Glomeromycetes

Formerly considered zygomycetes, but analysis of hundreds of fungal genomes put these into a separate monophyletic clade. They have arbuscular mycorrhizae. 160 known species, all are endomycorrhizae called arbuscular mycorrhizae that are symbiotic with plant roots. About 90% of all known plants have them.

Chitin

Fungal hyphae have cell walls, these are built mainly of chitin, a strong but flexible nitrogen-containing polysaccharide, identical to that found in arthropods. The adaptive advantage associated with the filamentous nature of fungal mycelia is primarily related to an extensive surface area well suited for invasive growth and absorptive nutrition.

Saprobic Fungi

Fungi absorb nutrients from nonliving organisms.

Parasitic Fungi

Fungi absorb nutrients from the cells of living hosts. Some parasitic fungi, including some that infect humans and plants, are pathogenic.

Mutualistic Fungi

Fungi also absorb nutrients from a host organism, but they reciprocate with functions that benefit their partner in some way. Some fungal species can kill herbivores while feeding off of sugars from its plant host. Examples: fungi can help increase drought tolerance in plants, fungi help break down wood in the guts of termites. Endophytes in leaves produce toxins that deter herbivores. Fungi help break down plant material in the guts of grazing mammals.

Fungi

Fungi are eukaryotes and most are multicellular. Fungi are heterotrophic and absorb their nutrients. While once groups with plants, fungi generally differ from other eukaryotes in nutritional mode, structural organization, growth, and reproduction. Molecular studies indicate that animals, not plants, are closer relative of fungi. Fungi are heterotrophs that acquire nutrients by absorbing small molecules from the surrounding medium. Fungi have an extremely high surface-area-to-volume ratio. The larger surface area allows for more material to be transported through the cell membrane. Roles are decomposition and predation. Plants are harmed by fungal pathogens. Plant depend on fungi as mutualistic symbionts. If all fungi in an environment perform decomposition were to suddenly die, then prokaryotes would benefit most, due tot eh fact that their fungal competitors have been removed. The diploid phase of the life cycle is shortest in fungus, most fungi are haploid except for a very brief diploid stage that is seen only when fungus reproduces sexually.

Absorptive Nutrition

Fungi are heterotrophs that acquire their nutrients by absorption. They absorb small organic molecules from the surrounding medium. The absorptive mode of nutrition is associated with the ecological roles of fungi as decomposers (saprobes), parasites or mutualistic symbionts. Extensive surface area and rapid growth adapt fungi for absorptive nutrition.

Beneficial Attributes of Fungi

Fungi decompose dead organisms, fallen leaves, feces, and other organic materials. Recycle vital chemical elements back to the environment in forms other organisms can assimilate. Most plants depend on mutualistic fungi that help their roots absorb minerals and water form the soil. Humans have cultivated fungi for centuries for food, to produce antibiotics and other drugs, to make bread rise and to ferment beer and wine. Both fungi and arthropods use chitin for support.

Coenocytic

Fungi that lack septa, consist of a continuous cytoplasmic mass with hundreds or thousands of nuclei. This results from repeated nuclear division without cytoplasmic division.

karyogamy

Fusion of nuclei. Fungi disperse and reproduce by releasing spores that are produced sexually. This is in many fungi with sexual life cycles, karyogamy, fusion of haploid nuclei contributed by two parents, occurs well after plasmogamy. The delay may be hours, day, or years.

Commercially Important Fungi

In addition to the benefits that we receive from fungi in their roles as decomposers and recyclers of organic matter, we use fungi in a number of ways. Most people have eaten mushrooms, the fruiting bodies ( basidiocarps) of subterranean fungi. Some mushrooms have toxins, potentially deadly. Hallucinogenic mushrooms used medicinally to relieve anxiety and fear of death in terminal cancer patients to help with PTSD, even to help patients quit smoking. Self-created air current help mushrooms disperse their spores. Mushrooms can increase the moisture of the air around them, creating convection current that make their own wind in order to help their spores disperse over a wide area.

heterokaryotic

In most fungui, karyogamy does not immediately follow plasmogamy, which consequently results in this heterokaryotic or dikaryotic cells. Many fungi have a heterokaryotic stage. The nuclei of fungal hyphae and spores of most species are haploid, except for transient diploid stages that form during sexual life cycles. However, some mycelia become genetically heterogenous through the fusion of two hyphae that have genetically different nuclei. In this heterokaryotic mycelium, the nuclei may remain in separate parts of the same mycelium or mingle and even exchange chromosomes and genes. One haploid genome may be able to compensate for harmful mutations in the other nucleus.

Mycelium

Interwoven mat of hyphae. Fungal mycelia can be huge, but they usually escape notice because they are subterranean. One giant individual of Armillaria ostoyae in Oregon is 3.4 miles in diameter and covers 2,200 acres of forest. It is at least 2,400 years old and weight hundreds of tons.

Four Fungal Forms

Molds, yeasts, lichens, and mycorrihizae are specialized lifestyles that evolved independently in diverse fungal taxa. Have evolved morphological and ecological adaptation for specialized ways of life. These have occurred independently among the zygote, fungi , sac fungi, and club fungi.

5 Phyla of Fungi

More than 100,000 species of fungi are known and mycologists estimate that there are actually about 1.5 million species worldwide. Molecular analyses supports the division of the fungi into: Chytrids (1,000 species), Zygomycetes (1,000 species), Glomermycetes (160 species), Ascomycetes (65,000 species), Basidiomycetes (30,000 species).

haustoria

Parasitic fungi usually have some hyphae modified as haustoria, nutrient-absorbing hyphal tips that penetrate the tissues of their host. Some fungi even have hyphae adapted for preying on animals.

chytrids

Phylum Chytridiomycota, chytrids may provide clues about fungal origins. Htey have motild spores with flagella. The chytrids are mainly aquatic. Some are saprobes, while others parasitize protists, plants, and animals. The presence of flagellated zoospores had been used as evidence for excluding chytrids from kingdom Fungi which lack flagellated cells. However recent molecule evidence supports the hypothesis that chytrids are the most primitive fungi. Like other fungi, chytrids used an absorptive mode of nutrition and have chitinous cells walls. While there are a few unicellular chytrids, most form coenocytic hyphae. Some key enzymes and metabolic pathways found in chytrids are shared with other fungal groups, but not with the so-called fungus-like protists. An invasive aquatic chytrid fungus is currently causing a mass extinction of frogs and salamanders all over the world.

Zygomycetes

Phylum zygomycota, zygote fungi form resistant structures during sexual reproduction, resistant zygosporangium as sexual stage. Most of the 600 zygomycete are terrestrial living in soil or on decaying plant and animal material. Zygomycete hyphae are coencytic, with septa found only in reproductive structures. The zygomycete Rhizopus can reproduce either asexually or sexually.

Ascomycetes

Sac like fungi produce sexual spores in saclike asci. Mycologists have described over 60,000 species of ascomycetes or sac fungi. They range in size and complexity from unicellular yeasts to elaborate cup fungi and morels. They are exolofically diverse. Some are devastating plant pathogens. Many are important saprobes, particularly if plant material. About half the ascomycete species live with algae in mutualistic associations called lichens. Some ascomycetes form mycorrhizae with plants or livve between mesophyll cells in leaves where they may help protect the plant tissue from insects by releasing toxins. Some Ascomycetes are among the most sought-after wild foods, such as black truffles. White truffles are said to be the most expensive food in the world-currently they go for about $3600 a pound. Ascomycetes are characterized by an extensive heterokaryotic stage during the formation of ascocarps and by the ascocarp itself ( a sac-like structure that hold the spores).

dikaryotic

The life cycle of a basiodiomycete usually includes a long-lived dikaryotic mycelium. As in ascomycetes, this extended dikaryotic stages provides many opportunities for genetic recombination events, in effect multiplying the result of a single mating.

hyphae

The vegetative bodies of most fungi are constructed of tiny filaments called hyphae that form an interwoven mat called a mycelium. Fungal hyphae have cell walls.

Humongous Fungus

World famous, earth's largest organism, a single fungus organisms in Oregon covers 2384 acres as big as 1665 football fields.

Basidium

a transient diploid stage. The significance of a transient diploid state in fungi is these sexual processess generate genetic variation. The sexual process of karyogamy and meiosis generate extensive genetic variation, a prerequisite for natural selection.

yeasts

are unicellular fungi that inhabit liquid or moist habitats, including plant sap and animal tissues. Yeasts reproduce asexually by simple cell division or budding off a parent cell. Some yeast reproduce sexually, forming asci (Ascomycota) or basidia (Basidiomycota), but others have no known sexual stage (imperfect fungi).

septa

most fungi are multicellular with hyphae divided into cells by cross walls or septa. These generally have pores large enough for ribosomes, mitochondria and even nuclei to flow from cell to cell

Mycorrihizae

mutualistic associations of plant roots and fungi, which enhance the absorption of nutrients and water. The anatomy of this symbiosis depends on the type of fungus. The extensions of the fungal mycelium from the mycorrhizae greatly increase the absorptive surface of the plant roots. The fungus provides minerals from the soil for the plant, and the plant provides organic nutrients. Mycorrihizae are enormously important in natural ecosystems and in agriculture. Almost all vascular plants have mycorrhizae and the Basidiomycota, Ascomycota, and Zygomycota all have members that form mycorrhizae. The fungi in these permanent associations periodicaly form fruiting bodies for sexual reproduction. Plant growth without mycorrhizae is often stunted.

Exoenzymes

powerful hydrolytic enzymes secreted by the fungus, digest food outside its body to simpler compounds that the fungus can absorb and use.