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Fungal Diversity I. Introduction II. Fungal Phyla

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1 Fungal Diversity I. Introduction II. Fungal Phyla
Reading: Chap. 31 I. Introduction A. What is a fungus? B. What does a fungus do? C. Basic fungal life cycle D. Who cares about fungi? II. Fungal Phyla A. Overview B-E. Life cycles of the phyla III. Fungal mutualisms A. Lichens B. Mycorrhizae Fungal Diversity II. Ecological importance: A. base of the food chain in aquatic ecosystems, both marine and freshwater; populations are controlled by seasonal climate shifts, predation, or nutrient limitation. Many very productive aquatic habitats - antarctic oceans, areas of upwelling off the Pacific coasts of N and S America are so because of abundant nutrients for phytoplankton. [Starr, fig. 37.3, OH 357]

2 Characteristics of Fungi
Non-motile eukaryotes lacking chlorophyll Contain nucleus, mitochondria, 80S ribosomes Plasma membrane contains ergosterol instead of cholesterol. Cell wall is composed of chitin and various glucans, mannans, and complex polysaccharides Larger than bacteria Relatively simple nutritional requirements, wide range of growth rates Form visible colonies in days to weeks Unicellular or multicellular depending on the species

3 Molds Multicellular, tubular structures (hyphae)
Hyphae can be septate (regular crosswalls) or nonseptate (coenocytic) depending on the species (grow by apical extension) Vegetative hyphae grow on or in media (absorb nutrients); form seen in tissue, few distinguishing features Aerial hyphae contain structures for production of spores (asexual propagules); usually only seen in culture

4 Fungi The parts: Fig. 31.1 Cell walls - made of chitin. Same material that is in the external skeletons of arthropods - insects, arachnids, and crustaceans.

5 Molds - identification
Identification based on colony morphology (pigment, texture) and morphology of reproductive structures Conidia - spores formed by budding (blastoconidia) or disarticulation of existing hypha (arthroconidia) Sporangiospores - produced by free-cell formation within sporangium in nonseptate molds 1 1 Conidiopspores Phialides Vesicle Conidiophore Septate hyphae 3 sporangium sporangiophore Endospores Nonseptate hyphae 5. rhizoids 2 3 4 2 5 4 5

6 YEASTS Also yeasts - single-celled e.g., Saccharomyces cerevisiae
Candida albicans 31.15

7 Yeasts Unicellular, 3-5 µm, reproduce by budding (blastoconidia formation) or fission Identified by microscopic morphology (grow on cornmeal agar) and biochemical tests (sugar assimilation, enzymatic activity). Molds and yeast are not exclusive forms, some species may exist in both yeast and mold forms (dimorphism).

8 Colonial Morphology of Fungi
Cryptococcus neoformans Trichophyton tonsurans Wangiella dermatitidis Candida albicans T. menta-grophytes Aspergillus fumigatus

9 FUNGAL LIFE CYCLE Asexual - budding or cell division Sexual - fusion of 2 mating types spore formation

Organic compounds needed for growth saprophytes as feed on dead organic matter Adapted to: growth at pH growth on surfaces growth under high osmotic conditions growth at low water levels growth in low nitrogen environments growth on unusual nutrient sources

11 B. What does a fungus do? Absorptive heterotroph Such as: Mutualist
Parasite/pathogen Mutualist Detritivore

12 Also eat: - wood in houses, boats, fences; - food; - other materials - cloth, paint, leather, waxes, jet fuel, petroleum, paper, wire insulation, photographic film, - to name a few. What do all of these materials have in common? They are all C-based.

13 C. Basic fungal life cycle
2. Fertilization doesn’t happen all at once Plasmogamy - fusion of cytoplasm Karyogamy - fusion of nuclei (gametes) heterokaryotic dikaryotic fig. 31.2

14 Classification of Fungi
Taxonomy is based on structural features of the teleomorph (sexual phase). Zygomycota - includes all fungi with nonseptate hyphae Ascomycota - includes most human pathogens Basidiomycota - mainly saprobes or plant pathogens Deuteromycota (fungi imperfecti) Sexual phase unknown or doesn’t exist. Some can be assigned to above groups based on phylogenetic analysis.

15 B. Zygomycota 1. No dikaryotic growth
2. Both sexual and asexual sporangia

16 C. Ascomycota - Life cycle
1. Dikaryotic growth 2. Fruiting body: ascocarp 3. Fertile layer with asci 4. Eight ascospores per ascus (sac) 5. Asexual reproduction via conidia

17 D. Basidiomycota - Life cycle
1. Dikaryotic growth 2. Fruiting body: basidiocarp 3. Fertile layer on gills with basidia (“clubs”) 4. Four spores per basidium 5. Asexual reproduction is rare

18 E. Deuteromycota - “fungi imperfecti”
1. Not a true phylum (not a natural group): polyphyletic 2. Fungi with no known sexual reproduction 3. Asexual reproduction by conidia

19 III. Fungal mutualisms Definitions:
Symbiosis - 2 organisms living together in intimate physical contact Mutualism - both organisms benefit from the relationship Parasitism - one benefits, one loses Commensalism - one benefits, other not affected

20 A. Lichens 1. Partners a. Fungal partner - gives protection
- mostly Ascomycetes (~25,000 spp.) - only found in lichens (not free-living) b. Photosynthetic partner - gives fixed carbon (sugars) - green alga or cyanobacterium - can be free-living

21 A. Lichens 2. Anatomy a. most of lichen body is fungal hyphae
b. photosynthetic partner in a distinct layer c. sexual reproduction of fungal partner only d. asexual reproduction: soredia, fragmentation 2. Anatomy medulla

22 Figure 29.9a Ectomycorrhizal fungi (EMF) Root cells EMF Figure: 29.9a
Caption: (a) Ectomycorrhizal fungi (EMF) form a dense network around the roots of plants. The combination of root and fungus is called a mycorrhiza. The drawing shows how the interaction works in EMF. Note that their hyphae penetrate the intercellular spaces of the root, but do not enter the cells themselves.  EMF

23 A. Lichens 3. Morphology fruticose crustose foliose

24 A. Lichens 4. Importance a. rock weathering, soil formation in primary succession - acid secretion - trapping particulates nitrogen fixation (cyanobacteria) b. Indicators: susceptible to pollutants

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