Transcript Ch31-2
Matt Ponzini, Shane D’Cruz, and Nikhil Popat Diversity of Fungi 100,000+ species of Fungi are known (Estimated to be 1.5 Million worldwide) Fungi Classified into 4 divisions 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 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 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 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 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 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. 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