24: Fungi Flashcards
Characteristics of Fungi, Classifications of Fungi, Ecology of Fungi, Fungal Parasites and Pathogens, Importance of Fungi in Human Life (175 cards)
1
Q
How many species of fungi are there?
A
The kingdom Fungi includes an enormous variety of living organisms collectively referred to as Eumycota, or true Fungi. While scientists have identified about 100,000 species of fungi, this is only a fraction of the 1.5 million species of fungus likely present on Earth.
2
Q
What are some examples of fungi?
A
Edible mushrooms, yeasts, black mold, and the producer of the antibiotic penicillin, Penicillium notatum, are all members of the kingdom Fungi.
3
Q
Are fungi autotrophic or heterotrophic?
A
Fungi are not capable of photosynthesis; they are heterotrophic because they use complex organic compounds as sources of energy and carbon.
4
Q
What are the fungi reproduction strategies?
A
Some fungal organisms multiply only asexually, whereas others undergo both asexual reproduction and sexual reproduction with alternation of generations. Most fungi produce a large number of spores, which are haploid cells that can undergo mitosis to form multicellular, haploid individuals.
5
Q
What are mycorrhizae?
A
A mutualistic relationship between a plant and a fungus. Mycorrhizae are connections between fungal hyphae, which provide soil minerals to the plant, and plant roots, which provide carbohydrates to the fungus.
6
Q
What is Dutch elm disease?
A
A serious infection caused by the fungus Ophiostoma ulmi. It is a particularly devastating type of fungal infestation that destroys many native species of elm (Ulmus sp.). The fungus infects the vascular system of the tree, which blocks water flow within the plant and mimics drought stress. The elm bark beetle acts as a vector, transmitting the disease from tree to tree. Accidentally introduced in the early 1930s, the fungus decimated elm trees across the continent. Many European and Asiatic elms are less susceptible to Dutch elm disease than American elms.
7
Q
What is the impact of fungal infections on humans?
A
In humans, fungal infections are generally considered challenging to treat. Unlike bacteria, fungi do not respond to traditional antibiotic therapy, since they are eukaryotes. Fungal infections may prove deadly for individuals with compromised immune systems.
8
Q
What are some of the commercial applications of fungi?
A
The food industry uses yeasts in baking, brewing, and cheese and wine making. Many industrial compounds are byproducts of fungal fermentation. Fungi are the source of many commercial enzymes and antibiotics.
9
Q
What is a spore?
A
A haploid cell that can undergo mitosis to form a multicellular, haploid individual.
10
Q
What is a coenocytic hypha?
A
Single hypha that lacks septa and contains many nuclei.
11
Q
What are facultative anaerobes?
A
Organisms that can perform both aerobic and anaerobic respiration and can survive in oxygen-rich and oxygen-poor environments.
12
Q
What is a haustoria?
A
Modified hypha on many parasitic fungi that penetrate the tissues of their hosts, release digestive enzymes, and/or absorb nutrients from the host.
13
Q
What does it mean to be heterothallic?
A
Describes when only one mating type is present in an individual mycelium.
14
Q
What does it mean to be homothallic?
A
Describes when both mating types are present in mycelium.
15
Q
What is a hypha?
A
Fungal filament composed of one or more cells. Plural: hyphae.
16
Q
What is karyogamy?
A
Fusion of nuclei.
17
Q
What is a mycelium?
A
Mass of fungal hyphae.
18
Q
What is mycology?
A
Scientific study of fungi.
19
Q
What are obligate aerobes?
A
Organisms, such as humans, that must perform aerobic respiration to survive.
20
Q
What are obligate anaerobes?
A
Organisms that only perform anaerobic respiration and often cannot survive in the presence of oxygen.
21
Q
What is plasmogamy?
A
Fusion of cytoplasm.
22
Q
What is a saprobe?
A
Organism that derives nutrients from decaying organic matter; also saprophyte.
23
Q
What is a septum?
A
Cell wall division between hyphae. Plural: septa
24
Q
What is a sporangium?
A
Reproductive sac that contains spores.
25
What is a thallus?
Vegetative body of a fungus. May be unicellular or multicellular.
26
What is a yeast?
General term used to describe unicellular fungi.
27
What are some reasons why fungi were previously classified as plants?
Fungi arose mostly sessile and seemingly rooted in place. They possess a stem-like structure similar to plants, as well as having a root-like fungal mycelium in the soil.
28
When did fungi first evolve?
Based on fossil evidence, fungi appeared in the pre-Cambrian era, about 950 million years ago.
29
Where are fungi found in the phylogenetic tree?
Molecular biology analysts of the fungal genome demonstrates that fungi are more closely related to animals than plants. They are a polyphyletic group of organisms that share characteristics, rather than sharing a common ancestor.
30
Which degrees are usually required to become a mycologist?
Mycology is a branch of microbiology, and many mycologists start their careers with a degree in microbiology. To become a mycologist, a bachelor's degree in a biological science (preferably majoring in microbiology) and a master's degree in mycology are minimally necessary.
31
What are some fields that mycologists can specialize in?
Taxonomy and fungal genomics, molecular and cellular biology, plant pathology, biotechnology, or biochemistry.
32
In what ways may mycologists practice medicine?
Some medical microbiologists concentrate on the study of infectious diseases caused by fungi (mycoses).
33
What are some examples of fungal infections identified and controlled by mycologists in collaboration with cross-disciplinary scientists?
Mycologists collaborate with zoologists and plant pathologists to identify and control difficult fungal infections, such as the devastating chestnut blight, the mysterious decline in frog populations in many areas of the world, or the deadly epidemic called white nose syndrome, which is decimating bats in the eastern United States.
34
What are some ways in which mycologists are employed in the public sector?
Government agencies hire mycologists as research scientists and technicians to monitor the health of crops, national parks, and national forests.
35
What are some ways in which mycologists are employed in the private sector?
Mycologists are employed in the private sector by companies that develop chemical and biological control products or new agricultural products, and by companies that provide disease control services.
36
Why are mycologists employed in the food industry?
Because of the key role played by fungi in the fermentation of alcohol and the preparation of many important foods, scientists with a good understanding of fungal physiology routinely work in the food technology industry.
37
How is mycology used in wine-making?
Oenology, the science of wine making, relies not only on the knowledge of grape varietals and soil composition, but also on a solid understanding of the characteristics of the wild yeasts that thrive in different wine-making regions. It is possible to purchase yeast strains isolated from specific grape-growing regions.
38
Who discovered the process of fermentation?
The great French chemist and microbiologist, Louis Pasteur, made many of his essential discoveries working on the humble brewer's yeast, thus discovering the process of fermentation.
39
Does horizontal gene transfer occur in fungi?
A few types of fungi have structures comparable to bacterial plasmids, however the horizontal transfer of genetic information from one mature fungus to another rarely occurs in fungi.
40
In what ways do fungal cells differ from plant cells?
Unlike plant cells, fungal cells do not have chloroplasts or chlorophyll.
41
What are some properties of fungal pigments?
Many fungi display bright colors arising from other cellular pigments, ranging from red to green to black. Pigments in fungi are associated with the cell wall and play a protective role against ultraviolet radiation. Some fungal pigments are toxic.
42
What is *Amanita muscaria* (fly agaric)?
A poisonous mushroom native to temperate and boreal regions of North America that is recognizable by its bright red cap and white patches.
43
What are some properties of fungal cell walls?
Like plant cells, fungal cells have a thick cell wall. The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans. Chitin, also found in the exoskeleton of insects, gives structural strength to the cell walls of fungi. The wall protects the cell from desiccation and predators.
44
How do the plasma membranes of fungal cells differ from those of animal cells?
Fungi have plasma membranes similar to other eukaryotes, except that the structure is stabilized by ergosterol: a steroid molecule that replaces the cholesterol found in animal cell membranes.
45
What is the motility of fungi?
Most members of the kingdom Fungi are nonmotile. Flagella are produced only by the gametes in the primitive phylum Chytridiomycota.
46
What are dimorphic fungi?
Dimorphic fungi can change from the unicellular to multicellular state depending on environmental conditions.
47
What are some examples of unicellular fungi?
*Saccharomyces cerevisiae* (baker's yeast) and the *Candida* species, including *Candida albicans* (the agent of candidiasis and thrush, a common fungal infection)
48
What are the morphological stages of multicellular fungi?
Most fungi are multicellular organisms. They display two distinct morphological stages: the vegetative and reproductive. The vegetative stage consists of a tangle of slender thread-like structures called hyphae, whereas the reproductive stage can be more conspicuous.
49
How large are hyphae?
Although individual hyphae must be observed under a microscope, the mycelium of a fungus can be very large.
50
What is *Armillaria ostoyae/Armillaria solidipes* (honey mushroom)?
A giant fungus that is considered to be the largest organism on Earth, spreading across more than 2000 acres of underground soil in eastern Oregon. It is estimated to be at least 2400 years old.
51
What is the effect of *Neotestudina rosati* on humans?
The mycelium of the fungus *Neotestudina rosati* can be pathogenic to humans. The fungus enters through a cut or scrape and develops a mycetoma, a chronic subcutaneous infection.
52
Are fungal hyphae separated by septa?
Most fungal hyphae are divided into separate cells by endwalls called septa (septated). In most phyla of fungi, tiny holes in the septa allow for the rapid flow of nutrients and small molecules from cell to cell along the hypha. They are described as perforated septa. The hyphae in bread molds (which belong to the phylum *Zygomycota*) are not separated by septa. Instead, they are formed by large cells containing many nuclei, an arrangment described as coenocytic hyphae.
53
In which environmental conditions can fungi be found?
Fungi thrive in environments that are moist and slightly acidic, and can grow with or without light. They vary in their oxygen requirement. Most fungi are obligate aerobes, other species are obligate anaerobes, and some are intermediate, being facultative anaerobes.
54
What is an example of fungi that are obligate anaerobes?
The chytridiomycetes that reside in the rumen of cattle are obligate anaerobes.
55
Do yeasts require oxygen?
Yeasts are facultative anaerobes. The alcohol produced from yeast fermentation is used in wine and beer production.
56
In what ways is fungal nutrition similar to animal nutrition?
Like animals, fungi are heterotrophs; they use complex organic compounds as a source of carbon, rather than fix carbon dioxide from the atmosphere as do some bacteria and most plants. In addition, fungi do not fix nitrogen from the atmosphere. Like animals, they must obtain it from their diet. As with animal cells, the polysaccharide of storage is glycogen, rather than starch, as found in plants.
57
In what ways is fungal nutrition different from that of animals?
Unlike most animals, which ingest food and then digest it internally in specialized organs, fungi perform these steps in the reverse order; digestion precedes ingestion. First, exoenzymes are transported out of the hyphae, where they process nutrients in the environment. Then, the smaller molecules produced by this external digestion are absorbed through the large surface area of the mycelium.
58
What role do fungi play in an ecosystem?
Fungi are mostly saprobes; they obtain their nutrients from dead or decomposing organic matter: mainly plant material. Fungal exoenzymes are able to break down insoluble polysaccharides, such as the cellulose and lignin of dead wood, into readily absorbable glucose molecules. The carbon, nitrogen, and other elements are thus released into the environment.
59
How can fungi be used in bioremediation?
Because of their varied metabolic pathways, fungi fulfill an important ecological role and are being investigated as potential tools in bioremediation. For example, some species of fungi can be used to break down diesel oil and polycyclic aromatic hydrocarbons (PAHs). Other species take up heavy metals, such as cadmium and lead.
60
What are some examples of parasitic fungi in plants?
Smut and Dutch elm disease.
61
What are some examples of parasitic fungi in humans?
Athlete's foot and candidiasis (thrush).
62
What are some nutrition strategies for fungi in nitrogen-poor environments?
In environments poor in nitrogen, some fungi resort to predation of nematodes (small non-segmented roundworms). Species of *Arthrobotrys* fungi have a number of mechanisms to trap nematodes. One mechanism involves constricting rings within the network of hyphae. The rings swell when they touch the nematode, gripping it in a tight hold. The fungus penetrates the tissue of the worm by extending specialized hyphae called haustoria.
63
What are perfect vs. imperfect fungi?
Perfect fungi reproduce both sexually and asexually, while the so-called imperfect fungi reproduce only asexually (by mitosis).
64
In which type of reproduction are fungal spores produced?
In both sexual and asexual reproduction.
65
What are some ways in which spores are dispersed?
Fungi produce spores that disperse from the parent organism by either floating on the wind or hitching a ride on an animal.
66
How large are fungal spores compared to plant seeds?
Fungal spores are smaller and lighter than plant seeds.
67
What are three ways that asexual reproduction is performed in fungi?
Fungi reproduce asexually by fragmentation, budding, or producing spores. Fragments of hyphae can grow new colonies. Somatic cells in yeast form buds.
68
How is budding performed in fungi?
During budding (a type of cytokinesis), a bulge forms on the side of the cell, the nucleus divides mitotically, and the bud ultimately detaches itself from the mother cell.
69
What is *Histoplasma capsulatum*?
A pathogenic yeast that primarily infects lungs but can spread to other tissues, causing histoplasmosis, a potentially fatal disease.
70
How are spores used by fungi in asexual reproduction?
The most common mode of asexual reproduction is through the formation of asexual spores. Spores allow the fungi to expand their distribution and colonize new environments. They may be released from the parent thallus either outside or within a special reproductive sac called a sporangium.
71
What is the fungi life cycle?
First, there is a (1*n*) mycelium. During sexual reproduction, there are three stages which lead to formation of haploid (1*n*) spores: plasmogamy, karyogamy, and meiosis. During germination, a multi-cellular (1*n*) mycelium is formed. Sexual reproduction may be repeated, or asexual reproduction may occur, where mitosis generates spores, which then germinate into (1*n*) mycelia.
72
What are the different types of asexual spores?
Conidiospores are unicellular or multicellular spores that are released directly from the tip or side of the hypha. Other asexual spores originate in the fragmentation of a hypha to form single cells that are released as spores; some of these have a thick wall surrounding the fragment. Yet others bud off the vegetative parent cell. Sporangiospores are produced in a sporangium.
73
Why does sexual reproduction occur in fungi?
Sexual reproduction introduces genetic variation into a population of fungi. In fungi, sexual reproduction often occurs in response to adverse environmental conditions.
74
How are mating types used by fungi in sexual reproduction?
During sexual reproduction, two mating types are produced. When both mating types are present in the same mycelium, it is called homothallic, or self-fertile. Heterothallic mycelia require two different, but compatible, mycelia to reproduce sexually.
75
What are the stages of sexual reproduction?
Although there are many variations in fungal sexual reproduction, all include the following three stages. First, during plasmogamy (literally, "marriage or union of cytoplasm"), two haploid cells fuse, leading to a dikaryotic stage where two haploid nuclei coexist in a single cell. During karyogamy ("nuclear marriage"), the haploid nuclei fuse to form a diploid zygote nucleus. Finally, meiosis takes place in the gametangia (singular, gametangium) organs, in which gametes of different mating types are generated. At this stage, spores are disseminated into the environment.
76
What is used to stabilize plant plasma membranes?
Phytosterols (similar to cholesterol in animals and ergosterol in fungi).
77
What are arbuscular mycorrhizae?
Mycorrhizae commonly involving glomeromycetes in which the fungal hyphae penetrate the cell walls of the plant root cells (but not the cell membranes).
78
What is an ascocarp?
Fruiting body of ascomycetes.
79
What is Ascomycota?
(Also, sac fungi) phylum of fungi that contains the majority of known fungi, and that store spores in an ascus (plural: asci), a sac-like structure that contains haploid ascospores.
80
What is a basidiocarp?
Fruiting body that protrudes from the ground and bears the basidia.
81
What is Basidiomycota?
(Also, club fungi) phylum of fungi that produce club-shaped structures (basidia) that contain spores.
82
What is a basidium?
The swollen terminal cell of a hypha in a basidiocarp.
83
What is Chytridiomycota?
(Also, chytrids) simplest and most primitive phylum of *Eumycota* (true fungi) that live in water and produce gametes with flagella.
84
What is Deuteromycota?
Former phylum of fungi that do not have a known sexual reproductive cycle (imperfect fungi - presently members of two phyla: Ascomycota and Basidiomycota).
85
What are ectomycorrhizae?
Mycorrhizal fungi that surround the roots with a mantle (similar to a sheath) and have a Hartig net that extends into the roots between cells (ecto="outside"), but that do not penetrate the root cells of the plant.
86
What is Glomeromycota?
Phylum of fungi that form symbiotic relationships with the roots of trees.
87
What is mold?
Tangle of visible mycelia with a fuzzy appearance.
88
What is Zygomycota?
(Also, conjugated fungi) relatively small phylum of fungi that form a zygote contained in a zygospore.
89
What is a zygospore?
Structure with a thick cell wall that contains the zygote in zygomycetes.
90
What properties and characteristics are used to classify fungi?
The kingdom Fungi contains five major phyla that were established according to their mode of sexual reproduction or using molecular data. Polyphyletic, unrelated fungi that reproduce without a sexual cycle, are placed for convenience in a sixth group called a "form phylum". Not all mycologists agree with this scheme. Rapid advances in molecular biology and the sequencing of 18S rRNA (a part of RNA) continue to show new and different relationships between the various categories of fungi.
91
What are the five true phyla of fungi?
The Chytridiomycota (Chytrids), the Zygomycota (conjugated fungi), the Ascomycota (sac fungi), the Basidiomycota (club fungi), and the recently described Phylum Glomeromycota.
92
What is the difference between "-mycota" and "-mycetes"?
"-mycota" is used to designate a phylum while "-mycetes" formally denotes a class or is used informally to refer to all members of the phylum.
93
When did chytrids evolve?
The evolutionary record shows that the first recognizable chytrids appeared during the late pre-Cambrian period, more than 500 million years ago.
94
What are some properties of chytrids?
Like all fungi, chytrids have chitin in their cell walls, but one group of chytrids has both cellulose and chitin in the cell wall. Most chytrids are unicellular; a few form multicellular organisms and hyphae, which have no septa between cells (coenocytic). They produce gametes and diploid zoospores that swim with the help of a single flagellum.
95
What is a zoospore?
A motile asexual spore that uses a flagellum for locomotion.
96
What is the ecological habitat of chytrids?
The ecological habitat and cell structure of chytrids have much in common with protists. Chytrids usually live in aquatic environments, although some species live on land. Some species thrive as parasites on plants, insects, or amphibians, while others are saprobes.
97
What is *Allomyces*?
A chytrid species whose reproductive cycle includes both asexual and sexual phases. *Allomyces* produces diploid or haploid flagellated zoospores in a sporangium.
98
What is *Rhizopus stolonifer*?
A zygomycete and familiar bread mold, which rapidly propagates on the surfaces of breads, fruits, and vegetables.
99
What is the ecological environment of zygomycetes?
Most species are saprobes, living off decaying organic material; a few are parasites, particularly of insects.
100
What commercial role do zygomycetes play?
The metabolic products of certain species of *Rhizopus* are intermediates in the synthesis of semi-synthetic steroid hormones.
101
What is the zygomycete life cycle?
In the beginning, there are spores. They may reproduce asexually or sexually. If asexually, mitosis ensues, forming mycelia, which then germinate into spores. If sexually, germination ensues, and mycelia form. If the two mating types (+ and –) are in close proximity, extensions called gametangia form between them. During plasmogamy, fusion between + and – mating types results in a zygosporangium with multiple haploid nuclei. The zygosporangium forms a thick, protective coat. In karyogamy, the nuclei fuse to form a zygote (2*n*) with multiple diploid nuclei. In meiosis and germination, a sporangium (1*n*) grows on a short stalk. Haploid spores are formed inside. Then germination occurs, and the cycle is repeated.
102
What is vegetative reproduction?
Any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or a specialized reproductive substructure.
103
How do zygomycetes reproduce?
Zygomycetes have a thallus of coenocytic hyphae in which the nuclei are haploid when the organism is in the vegetative stage. The fungi usually reproduce asexually by producing sporangiospores. The black tips of bread mold are the swollen sporangia packed with black spores. When spores land on a suitable substrate, they germinate and produce a new mycelium. Sexual reproduction starts when conditions become unfavorable. Two opposing mating strains (type + and type –) must be in close proximity for gametangia from the hyphae to be produced and fuse, leading to karyogamy. The developing diploid zygospores have thick coats that protect them from desiccation and other hazards. They may remain dormant until environmental conditions are favorable. When the zygospore germinates, it undergoes meiosis and produces haploid spores, which will, in turn, grow into a new organism. This form of sexual reproduction in fungi is called conjugation (although it differs markedly from conjugation in bacteria and protists), giving rise to the name "conjugated fungi".
104
What commercial role do ascomycetes play?
Many ascomycetes are of commercial importance. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies. *Aspergillus oryzae* is used in the fermentation of rice to produce sake.
105
In what ways do ascomycetes act as parasites?
Some ascomycetes parasitize plants and animals, including humans. For example, fungal pneumonia poses a significant threat to AIDS patients who have a compromised immune system. Ascomycetes not only infest and destroy crops directly; they also produce poisonous secondary metabolites that make crops unfit for consumption.
106
How are ascomycete hyphae structured?
Filamentous ascomycetes produce hyphae divided by perforated septa, allowing streaming of cytoplasm from one cell to the other. Conidia and asci, which are used respectively for asexual and sexual reproductions, are usually separated from the vegetative hyphae by blocked (non-perforated) septa.
107
How does reproduction occur in ascomycetes?
Asexual reproduction is frequent and involves the production of conidiophores that release haploid conidiospores. Sexual reproduction starts with the development of special hyphae from either one of two types of mating strains. The "male" strain produces an antheridium and the "female" strain develops an ascogonium. At fertilization, the antheridium and the ascogonium combine in plasmogamy without nuclear fusion. Special ascogenous, dikaryotic hyphae arise, in which pairs of nuclei migrate: one from the "male" strain and one from the "female" strain. In each ascus, two or more haploid ascospores fuse their nuclei in karyogamy. During sexual reproduction, thousands of asci fill a fruiting body called the ascocarp. The diploid nucleus gives rise to haploid nuclei by meiosis. The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia.
108
Why are mushroom-producing basidiomycetes sometimes referred to as "gill fungi"?
Because of the presence of gill-like structures on the underside of the cap, where the "gills" are actually compacted hyphae on which the basidia are borne.
109
What are some examples of Basidiomycota?
Smuts and rusts, which are important plant pathogens; toadstools, and shelf fungi stacked on tree trunks. Most edible fungi belong to the phylum Basidiomycota; however some basidiomycetes produce deadly toxins. For example, *Cryptococcus neoformans* causes severe respiratory illness.
110
What is a fairy ring?
The fruiting bodies of a basidiomycete forming in a ring. The best-known fairy ring fungus has the scientific name *Marasmius oreades*. The body of this fungus, its mycelium, is underground and grows outward in a circle. As it grows, the mycelium depletes the soil of nitrogen, causing the mycelia to grow away from the center and leading to the "fairy ring" of fruiting bodies where there is adequate soil nitrogen.
111
How do basidiomycetes reproduce?
The lifecycle of basidiomycetes includes alternation of generations. Spores are generally produced through sexual reproduction, rather than asexual reproduction. The club-shaped basidium carries spores called basidiospores. In the basidium, nuclei of two different mating strains fuse (karyogamy), giving rise to a diploid zygote that then undergoes meiosis. The haploid nuclei migrate into basidiospores, which germinate and generate monokaryotic hyphae. The mycelium that results is called a primary mycelium. Mycelia of different mating strains can combine and produce a secondary mycelium that contains haploid nuclei of two different mating strains. This is the dikaryotic stage of the basidiomyces lifecycle and it is the dominant stage. Eventually, the secondary mycelium generates a basidiocarp, which is a fruiting body that protrudes from the ground - this is what we think of as a mushroom. The basidiocarp bears the developing basidia on the gills under its cap.
112
What are some characteristics of deuteromycetes?
Since they do not possess the sexual structures that are used to classify other fungi, they are less well described in comparison to other members. Most members live on land, with a few aquatic exceptions. They form visible mycelia with a fuzzy appearance and are commonly known as mold.
113
How do deuteromycetes reproduce?
Reproduction of the fungi in this group is strictly asexual and occurs mostly by production of asexual conidiospores. Some hyphae may recombine and form heterokaryotic hyphae. Genetic recombination is known to take place between the different nuclei.
114
What impact do deuteromycetes have on humans?
The food industry relies on them for ripening some cheeses. The blue veins in Roquefort cheese and the white crust on Camembert are the result of fungal growth. The antibiotic penicillin was originally discovered on an overgrown Petri plate, on which a colony of *Penicillium* fungi killed the bacterial growth surrounding it. Other fungi in this group cause serious diseases, either directly as parasites (which infect both plants and humans), or as producers of potent toxic compounds, as seen in the aflatoxins released by fungi of the genus *Aspergillus*.
115
How do glomeromycetes function as symbionts?
Fossil records indicate that trees and their root symbionts share a long evolutionary history. It appears that all members of this family form arbuscular mycorrhizae: the hyphae interact with the root cells forming a mutually beneficial association where the plants supply the carbon source and energy in the form of carbohydrates to the fungus, and the fungus supplies essential minerals from the soil to the plant.
116
How do glomeromycetes reproduce?
The glomeromycetes do not reproduce sexually and do not survive without the presence of plant roots. Although they have coenocytic hyphae like the zygomycetes, they do not form zygospores. DNA analysis shows that all glomeromycetes probably descended from a common ancestor, making them a monophyletic lineage.
117
What are lichen?
Close association of a fungus (usually a member of the Ascomycota or Basidiomycota phyla) with a photosynthetic organism (a eukaryotic alga or a prokaryotic cyanobacterium) that benefits both partners.
118
What is a mycorrhiza?
Mutualistic association between fungi and vascular plant roots.
119
What are soredia?
Clusters of algal cells and mycelia that allow lichens to propagate.
120
In what habitats can fungi be found?
Although fungi are primarily associated with humid and cool environments that provide a supply of organic matter, they colonize a surprising diversity of habitats, from seawater to human skin and mucous membranes. Chytrids are found primarily in aquatic environments. Other fungi thrive in the dry and sandy soil of the southwestern United States. Fungi that parasitize coral reefs live in the ocean. However, most members of the Kingdom Fungi grow on the forest floor, where the dark and damp environment is rich in decaying debris from plants and animals. In these environments, fungi play a major role as decomposers and recyclers, making it possible for members of the other kingdoms to be supplied with nutrients and live.
121
How does fungal digestion facilitate their role as decomposers?
The ability of fungi to degrade many large and insoluble molecules is due to their mode of nutrition, as digestion precedes ingestion. Fungi produce a variety of exoenzymes to digest nutrients. The enzymes are either released into the substrate or remain bound to the outside of the fungal cell wall. Large molecules are broken down into small molecules, which are transported into the cell by a system of protein carriers embedded in the cell membrane. Because the movement of small molecules and enzymes is dependent on the presence of water, active growth depends on a relatively high percentage of moisture in the environment.
122
How do shelf fungi damage trees?
Shelf fungi, so called because they grow on trees in a stack, attack and digest the trunk or branches of a tree. While some shelf fungi are found only on dead trees, others can parasitize living trees and cause eventual death, so they are considered serious tree pathogens.
123
Which types of organisms do fungi form mutalistic associations with?
Fungi form mutualistic associations with many types of organisms, including cyanobacteria, algae, plants, and animals.
124
How many plant species engage in mycorrhizae?
Somewhere between 80 and 90% of all plant species have mycorrhizal partners.
125
How do fungi and plants benefit from mycorrhizae?
In mycorrhizal association, the fungal mycelia use their extensive network of hyphae and large surface area in contact with the soil to channel water and minerals from the soil into the plant. In exchange, the plant supplies the products of photosynthesis to fuel the metabolism of the fungus.
126
Which fungal phyla engage in ectomycorrhizae?
Ascomycota, Basidiomycota, and Zygomycota.
127
How do glomeromycetes engage in mycorrhizae?
Glomeromycete fungi form vesicular-arbuscular interactions with arbuscular mycorrhiza (sometimes called endomycorrhizae). In these mycorrhiza, the fungi form arbuscules that penetrate root cells and are the site of the metabolic exchanges between the fungus and the host plant. The arbuscules (from the Latin for little trees) have a shrub-like appearance.
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How do orchids engage in mycorrhiza?
Orchids are epiphytes that form small seeds without much storage to sustain germination and growth. Their seeds will not germinate without a mycorrhizal partner (usually a basidiomycete). After nutrients in the seed are depleted, fungal symbionts support the growth of the orchid by providing necessary carbohydrates and minerals. Some orchids continue to be mycorrhizal throughout their lifecycle.
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What are endophytes?
Fungi that live inside plant tissue without damaging the host. Endophytes release toxins that repel herbivores, or confer resistance to environmental stress factors, such as infection by microorganisms, drought, or heavy metals in soil.
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How are fungi thought to have affected the evolution of the root system in plants?
A well-accepted theory proposes that fungi were instrumental in the evolution of the root system in plants and contributed to the success of angiosperms. The bryophytes (mosses and liverworts), which are considered the most primitive plants and the first to survive on dry land, do not have a true root system; some have vesicular-arbuscular mycorrhizae and some do not. They depend on a simple rhizoid (an underground organ) and cannot survive in dry areas. True roots appeared in vascular plants. Vascular plants that developed a system of thin extensions from the rhizoids (found in mosses) are thought to have had a selective advantage because they had a greater surface area of contact with the fungal partners than the mosses and liverworts, thus availing themselves of more nutrients in the ground.
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How did mycorrhizae evolve?
Fossil records indicate that fungi preceded plants on dry land. The first association between fungi and photosynthetic organisms on land involved moss-like plants and endophytes. These early associations developed before roots appeared in plants. Slowly, the benefits of the endophyte and rhizoid interactions for both partners led to present-day mycorrhizae; up to about 90% of today's vascular plants have associations with fungi in their rhizosphere.
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Why are mycorrhizal fungi considered primitive?
The fungi involved in mycorrhizae display many characteristics of primitive fungi; they produce simple spores, show little diversification, do not have a sexual reproductive cycle, and cannot live outside of a mycorrhizal association.
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In which habitats are lichens found?
Lichens display a range of colors and textures and can survive in the most unusual and hostile habitats. They cover rocks, gravestones, tree bark, and the ground in the tundra where plant roots cannot penetrate. Lichens can survive extended periods of drought, when they become completely desiccated, and then rapidly become active once water is available again.
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What are the benefits of lichens to fungi and their photosynthetic partners?
Generally, neither the fungus nor the photosynthetic organism can survive alone outside of their symbiotic relationship. The body of a lichen, referred to as a thallus, is formed of hyphae wrapped around the photosynthetic partner. The photosynthetic organism provides carbon and energy in the form of carbohydrates. Some cyanobacteria fix nitrogen from the atmosphere, contributing nitrogenous compounds to the association. In return, the fungus supplies minerals and protection from dryness and excessive light by encasing the algae in its mycelium. The fungus also attaches the symbiotic organism to the substrate.
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How do lichens grow and reproduce?
The thallus of lichens grows very slowly, expanding its diameter a few millimeters per year. Both the fungus and the alga participate in the formation of dispersal units for reproduction called soredia, which are dispersed by wind and water and form new lichens.
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How can lichens be used to monitor air quality?
Lichens are extremely sensitive to air pollution, especially to abnormal levels of nitrogen and sulfur. The U.S. Forest Service and National Park Service can monitor air quality by measuring the relative abundance and health of the lichen population in an area.
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What ecological roles do lichens play?
Caribou and reindeer eat lichens, and they provide cover for small invertebrates that hide in the mycelia. In the production of textiles, weavers used lichens to dye wool for many centuries until the advent of synthetic dyes.
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How do fungi form mutualistic associations with arthropods?
Arthropods depend on the fungus for protection from predators and pathogens, while the fungus obtains nutrients and a way to disseminate spores into new environments.
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How do scale insects engage in mutualistic relationships with fungi?
The fungal mycelium of some species of Basidiomycota covers and protects the scale insect colonies. The scale insects foster a flow of nutrients from the parasitized plant to the fungus.
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How do leaf-cutting ants engage in mutualistic relationships with fungi?
The leaf-cutting ants of Central and South America literally farm fungi. They cut disks of leaves from plants and pile them up in gardens. Fungi are cultivated in these disk gardens, digesting the cellulose in the leaves that the ants cannot break down. Once smaller sugar molecules are produced and consumed by the fungi, the fungi in turn become a meal for the ants. The insects also patrol their garden, preying on competing fungi. Both ants and fungi benefit from the association. The fungus receives a steady supply of leaves and freedom from competition, while the ants feed on the fungi they cultivate.
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How are fungal spores dispersed via fungivores?
Animal dispersal is important for some fungi because an animal may carry spores considerable distances from the source. Fungal spores are rarely completely degraded in the gastrointestinal tract of an animal, and many are able to germinate when they are passed in the feces. Some dung fungi actually require passage through the digestive system of herbivores to complete their lifecycle.
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What is a black truffle?
The black truffle - a prized gourmet delicacy - is the fruiting body of an underground mushroom. Almost all truffles are ectomycorrhizal, and are usually found in close association with trees. Animals eat truffles and disperse the spores. In Italy and France, truffle hunters use female pigs to sniff out truffles. Female pigs are attracted to truffles because the fungus releases a volatile compound closely related to a pheromone produced by male pigs.
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Why does protection from light actually benefit the photosynthetic partner in lichens?
Protection from excess light that may bleach photosynthetic pigments allows the photosynthetic partner to survive in environments unfavorable to plants.
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What is commensalism?
Symbiotic relationship in which one member benefits while the other member is not affected.
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What is mycetismus?
Ingestion of toxins in poisonous mushrooms.
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What is mycosis?
Fungal infection.
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What is mycotoxicosis?
Poisoning by a fungal toxin released in food.
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What is parasitism?
Symbiotic relationship in which one member of the association benefits at the expense of the other.
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What is ergot?
A disease of cereal crops (especially of rye) caused by the fungus *Claviceps purpurea*. Although the fungus reduces the yield of cereals, the effects of the ergot's alkaloid toxins on humans and animals are of much greater significance. In animals, the disease is referred to as ergotism. The most common signs and symptoms are convulsions, hallucination, gangrene, and loss of milk in cattle. The active ingredient of ergot is lysergic acid, which is a precursor of the drug LSD.
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What are some examples of fungal pathogens that affect crops?
Ergot, smuts, rusts, and powdery or downy mildew.
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What is *Botrytis cinerea*?
The fungus that causes grey rot, which can destroy a grape crop. Controlled infection of grapes by *Botrytis*, however, results in noble rot, a condition that produces strong and much-prized dessert wines.
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What are aflatoxins?
Toxic, carcinogenic compounds released by fungi of the genus *Aspergillus*. Periodically, harvests of nuts and grains are tainted by aflatoxins, leading to massive recall of produce. This sometimes ruins producers and causes food shortages in developing countries.
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Where in animals do many fungal infections occur?
Many fungal infections are superficial; that is, they occur on the animal's skin. Termed cutaneous ("skin") mycoses, they can have devastating effects.
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What is *Batrachochytrium dendrobatidis*?
A chytrid fungus which infects the skin of frogs and presumably interferes with gaseous exchange. It is responsible for the decline of the world's frog population.
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What is *Pseudogymnoascus destructans*?
A cold-loving fungus which causes white-nose syndrome in bats, which appears as a white ring around the mouth of the bat. It has killed more than a million bats in the United States, and it disseminates its deadly spores in caves where bats hibernate.
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What are dermatophytes?
Fungi that cause the superficial mycoses of the epidermis, hair, and nails, but rarely spread to the underlying tissue. These fungi are often misnamed "dermatophytes", from the Greek words *dermis* meaning skin and *phyte* meaning plant, although they are not plants. Dermatophytes are also called "ringworms" because of the red ring they cause on skin. They secrete extracellular enzymes that break down keratin (a protein found in hair, skin, and nails), causing conditions such as athlete's foot and jock itch. These conditions are usually treated with over-the-counter topical creams and powders, and are easily cleared. More persistent superficial mycoses may require prescription oral medications.
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How do systemic mycoses work?
Systemic mycoses spread to internal organs, most commonly entering the body through the respiratory system.
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What is coccidioidomycosis (valley fever)?
Coccidioidomycosis (valley fever) is commonly found in the southwestern United States, where the fungus (*Coccidioides immitis*) resides in the dust. Once inhaled, the spores develop in the lungs and cause pneumonia with symptoms similar to those of tuberculosis.
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What is histoplasmosis?
Histoplasmosis is caused by the dimorphic fungus *Histoplasma capsulatum*. It also causes pulmonary infections, and in rarer cases, swelling of the membranes of the brain and spinal cord.
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What are opportunistic mycoses?
Fungal infections that are either common in all environments, or part of the normal biota. They mainly affect individuals who have a compromised immune system. Patients in the late stages of AIDS suffer from opportunistic mycoses that can be life threatening.
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What is *Candida*?
A yeast, and a common member of the natural biota, that can grow unchecked and infect the vagina or mouth (oral thrush) if the pH of the surrounding environment, the person's immune defenses, or the normal population of bacteria are altered.
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How can mushroom picking be dangerous?
Mycetismus can occur when poisonous mushrooms are eaten. It causes a number of human fatalities during mushroom-picking season. Many edible fruiting bodies of fungi resemble highly poisonous relatives, and amateur mushroom hunters are cautioned to carefully inspect their harvest and avoid eating mushrooms of doubtful origin. The adage "there are bold mushroom pickers and old mushroom pickers, but there are no old, bold mushroom pickers" is unfortunately true.
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Why can superficial mycoses in humans lead to bacterial infections?
Dermatophytes that colonize skin break down the keratinized layer of dead cells that protects tissues from bacterial invasion. Once the integrity of the skin is breached, bacteria can enter the deeper layers of tissues and cause infections.
164
How do fungi function as natural insecticides?
As animal pathogens, fungi help to control the population of damaging pests. These fungi are very specific to the insects they attack, and do not infect animals or plants. Fungi are currently under investigation as potential microbial insecticides, with several already on the market.
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What is *Beauveria bassiana*?
A fungus that is used as a pesticide and being tested as a possible biological control agent for the spread of emerald ash borer. *Beauveria bassiana* parasitizes emerald ash borers, appearing as white fuzz on the body of the insect. It has been released in a number of mid-western and eastern states.
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How are fungi used in agriculture and gardening?
Mycorrhizal fungi inoculants are available as soil amendments from gardening supply stores and are promoted by supporters of organic agriculture.
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How are fungi used in gastronomy?
Mushrooms figure prominently in the human diet. Morels, shiitake mushrooms, chanterelles, and truffles are considered delicacies. The humble meadow mushroom, *Agaricus campestris*, appears in many dishes. Molds of the genus *Penicillium* ripen many cheeses.
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How are fungi of the genus *Penicillium* used to ripen cheeses?
They originate in the natural environment such as the caves of Roquefort, France, where wheels of sheep milk cheese are stacked in order to capture the molds responsible for the blue veins and pungent taste of the cheese.
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What is a morel?
Ascomycete mushroom much appreciated for its delicate taste.
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How are fungi used in the production of beer and wine?
Fermentation - of grains to produce beer, and of fruits to produce wine - is an ancient art that humans in most cultures have practiced for millennia. Wild yeasts are acquired from the environment and used to ferment sugars into CO2 and ethyl alcohol under anaerobic conditions. It is possible to purchase isolated strains of wild yeasts from different wine-making regions.
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How did Louis Pasteur contribute to beer production?
Louis Pasteur was instrumental in developing a reliable strain of brewer's yeast, *Saccharomyces cerevisiae*, for the French brewing industry in the late 1850s. This was one of the first examples of biotechnology patenting.
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How are fungi used in medicine?
Many secondary metabolites of fungi are of great commercial importance. Antibiotics are naturally produced by fungi to kill or inhibit the growth of bacteria, limiting their competition in the natural environment. Important antibiotics, such as penicillin and the cephalosporins, are isolated from fungi. Valuable drugs isolated from fungi include the immunosuppressant drug cyclosporine (which reduces the risk of rejection after organ transplant), the precursors of steroid hormones, and ergot alkaloids used to stop bleeding.
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How are fungi used as hallucinogens?
Psilocybin is a compound found in fungi such as *Psilocybe semilanceata* and *Gymnopilus junonius*, which have been used for their hallucinogenic properties by various cultures for thousands of years.
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How are fungi used as model organisms?
As simple eukaryotic organisms, fungi are important model research organisms. Many advances in modern genetics were achieved by the use of the red bread mold *Neurospora crassa*. Additionally, many important genes originally discovered in *S. cerevisiae* served as a starting point in discovering analogous human genes. As a eukaryotic organism, the yeast cell produces and modifies proteins in a manner similar to human cells, as opposed to the bacterium *Escherichia coli*, which lacks the internal membrane structures and enzymes to tag proteins for export. This makes yeast a much better organism for use in recombinant DNA technology experiments. Like bacteria, yeasts grow easily in culture, have a short generation time, and are amenable to genetic modification.
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How did the development of modern yeast strains contribute to the production of artisinal breads?
Historically, artisinal breads were produced by capturing wild yeasts from the air. Prior to the development of modern yeast strains, the production of artisinal breads was long and laborious because many batches of dough had to be discarded, because the dough was often contaminated by toxic spores that float in the air. It was one of Louis Pasteur's achievements to purify reliable strains of baker's yeast to produce bread consistently.
