Download Ch31-2

Matt Ponzini, Shane D’Cruz, and
Nikhil Popat
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Diversity of Fungi
100,000+ species of
Fungi are known
(Estimated to be 1.5
Million worldwide)
Fungi Classified
into 4 divisions
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Division Chytridiomycota
Link between Fungi and Protists
Chytrids are mainly aquatic
Absent of flagellated cells as a membership requirement for Kingdom
Fungi
Chytrids are classified as Protists though
Recent studies show Chytrids and Fungi have similar sequences of
proteins and nucleic acids
Fungal Characteristics of Chytrids
Absorptive mode of nutrition
Cell walls made of chitin
Also contain some key enzymes and metabolic pathways common
among Fungi
Molecular evidence supports hypothesis that Chytrids are the most
primitive Fungi
Fungi evolved from Protists that had flagella --->Chytrids are only
Fungi retaining flagella
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Division Zygomycota
600 Zygomycetes
Mostly terrestrial ---> Live in Soil or decaying plant or animal material
Mycorrhizae- mutualistic associations with the roots of plants (Fig. 31.16; Pg. 585)
Black Bread Mold (Rhizopus stolonifer) is a common zygomycete
Hyphae spread out over food, penetrate it, and absorb nutrients
Bulbous Black Sporangia develop at the tip of the upright hyphae (Fig.
31.6; Pg. 578)
Hundreds of haploid spores develop and are dispersed
throughout the air
Spores that land on moist food germinate
If food is used up the Rhizopus reproduce sexually (Fig. 31.6; Pg. 578)
The zygosporangia are resistant to freezing and drying and are metabolically inactive.
When conditions approve haploid spores are released that colonize the new substrate.
Some zygomycetes can aim their spores. i.e. ---> Pilobolus
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Division Ascomycota
Over 600,000 species
Ascomycota- Sac Fungi
Live in Marine,
Freshwater, and Terrestrial
Habitats
Some of the most
devastating Pathogens
½ Live in symbiotic
associations with algae
called Lichens
Develop sexual spores in
Saclike Asci.
Ascocarps --->
Macroscopic Fruiting bodies
Coidia ---> Naked spores
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Basidiomycota
Approximately 25,000 fungi, including mushrooms, shelf fungi, puffballs, and rusts are
classified in the division Basidiomycota.
Basidium =A reproductive appendage that produces sexual spores on the gills of
mushrooms / Latin for “little pedestal”
Club-like shape of Basidium gives rise to the common name club fungus
Basidiomycetes are important decomposers of wood and other plant material
*includes: mycorrhiza (mutualistic associations of plant roots and fungi)-forming
mutualists and plant parasites
Saprobic basidiomycetes are best at decomposing wood
Rusts and Smuts are particularly destructive plant parasites
Life cycle of a club fungus usually includes a long lived dikaryotic mycelium
* mycelium (the densely branched network of hyphae [filaments that make up body of
fungus] in a fungus) with two haploid nuclei per cell, one from each parent
* mycelium reproduces sexual by producing elaborate fruiting bodies called
basidiocarps(Mushrooms are one example)
* A mushroom may release a billion basidiospores
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Molds are a type of fungus that grow rapidly and reproduce asexually
Myceli of these fungi grow as a saprobe or parasites on a variety of
substrates
Early in life a mold produces asexual spores
Mold applies to only these asexual stages and later the same fungus may
reproduce sexually, producing zygosporongia, ascocarps, or basidiocarps.
Unknown Molds: have no known sexual stages and are often referred to
as deuteromycetes(imperfect fungi).
*reproduce asexually by creating spores which they release
The most unusual fungi are predatory and trap and kill small protists/
animals(roundworms or nematodes)
Commercial Uses:
*Pharmaceutical companies grow mold in large liquid cultures and
extract antibiotics
*Penicillin is produced by ascomycetes belonging to a species of
Penicilium
*Other Penicilium species are important fermenters on the surface of
blue cheese, Brie and Camembert
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Yeasts
Yeasts are unicellular fungi that inhabit liquid or moist habitats, including
plant sap and animal tissues
They reproduce asexually by simple cell division or by the pinching of
small “bud cells” off a parent cell
Some yeasts reproduce sexually by forming asci or basidia, and are
classified as Ascomycota or Basidiomycota
Humans have used yeast to raise bread and ferment alcoholic beverages
for thousands of years, but only recently have they been separated into
pure cultures for more controlled human use
The yeast saccharomyces cerevisiae, an ascomycete, is the most important
of all human fungi
The tiny yeast cells are very active metabolically, and release small
bubbles of CO2 that leaven bread
Cultured anaerobically in breweries and wineries, Saccharomyces
ferments sugar to alcohol
Researchers also use it to study the molecular genetics of eukaryotes
because it is easy to culture and manipulate.
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Lichens
A lichen is a symbiotic association of millions of photosynthetic
microorganisms held together in a mesh of fungal hyphae
The fungal component is most commonly an ascomycete, but several
basidiomycete lichens are known.
The photosynthetic partners are usually unicellular or filamentous green
algae or cyanobacteria.
The merger of fungus and alga is so complete that lichens are actually
given genus and species names, as though they were single organisms.
Mycorrhizae
Mycorrhizae are mutualistic associations of plant roots and fungi
The word mycorrhizae means “fungus roots” referring to the structures
formed by both root cells and hyphae from the associated fungus
Mycorrhizae are extremely important in natural ecosystems and
agriculture
Over 95% of all vascular plants have mycorrhizae
Half of all species of mushroom-forming basidiomycetes live as
mycorrihizae with oak, birch, and pine trees