Chapter 12 The Eukaryotes: Fungi

Mitochondrion degenerates The Three-Domain System Eukarya Origin of mitochondria Fungi Animals Bacteria Origin of chloroplasts Amebae Mitochondria Slime molds Archaea Cyanobacteria Plants Ciliates Extreme halophiles Proteobacteria Green algae Chloroplasts Methanogens Dinoflagellates Hyperthermophiles Diatoms Gram-positive bacteria Euglenozoa Thermotoga Giardia Horizontal gene transfer occurred within the community of early cells. Mitochondrion degenerates Nucleoplasm grows larger

Domain Eukarya –Kingdom Fungi Yeasts, Molds and Mushrooms Eukaryotic First classified as plants, fungi are now considered different enough from plants to be placed in a separate kingdom Though the appearance of many fungi may resemble plants, they are probably more closely related to animals.

Mycology is the study of fungi Unicellular (yeasts) and multicellular. Fungi come in a wide variety of sizes and forms. Cell wall - chitin, glucans, mannans. Chemoheterotrophic – saprophytes and parasites Absorptive - Fungi secrete exoenzymes into the environment , than absorb the digested nutrients. Can metabolize complex carbohydrates Many fungi absorb nutrients directly from the soil. Many others feed on dead and decaying organisms (decomposers), and therefore have an important role in the recycling of nutrients in natural systems. Others feed on living organisms. Aerobic or facultative anaerobic. Nonmotile Have asexual and sexual reproductive cycles Develop from spores or hyphal fragments Resistant to osmotic pressure Preferred growing at pH 5 Many have great economic importance.

Morphological groups of Fungi 1. The single-celled fungi are yeasts 2. The multicellular fungi are molds 3. Dimorphism Grow as molds in vitro on artificial culture medium, but as yeasts in vivo in infected tissue.

1. Yeasts Unicellular fungi (nonfilamentous) Can use oxygen Capable of facultative anaerobic growth Asaxual reproduction - mitosis Fission yeasts divide symmetrically daughter cells separated by formation of a septa in the center (fission) Budding yeasts divide asymmetrically protuberance(bud) elongates parent cell’s nucleus divides one nuclei migrate to the bud cell wall material is then laid down between the bud and parent cell the bud eventually breaks away If fails to separate - pseudohyphae Sexual reproduction - meiosis Form zygote Form spores Figure 12.3

2. Multicellular Fungi The fungal thallus (body) consists of hyphae ( long filaments of cells joined together) A mass of hyphae is called mycelium. A hypha is a tubular structure that grows by elongation. Septate hyphae - contain cross-walls (septa) Coenocytic hyphae - contain no septa (long, continuous cells with many nuclei) Table 12.1

Mold mycelium Vegetative hyphae The portion that obtain nutrients Fungal hyphae have a small volume but large surface area, enhancing the fungal absorptive capacity Aerial hyphae The portion concerned with reproduction Produce spores Figure 12.2

3. Dimorphic fungi Pathogenic dimorphic fungi are yeast like at 37°C and mold like at 25°C Figure 12.4

Fungal Life Cycle Asexual reproduction (haploid cells) Sexual reproduction (diploid zygote)

Asexual reproduction Binary fission - fission yeast Budding – yeast By fragmentation (mold hyphae) Asexual spores (molds) Formed by individual fungi through mitosis ( exact copy of the parent) Formed on the ends of aerial hyphae of one organism

Asexual spores 1. Sporangiospore – spores are enclosed in a sac 2. Conidiospore - no sac Arthrospore fragmentation of septate hypha Blastoconidium buds coming off the parent cell Condida produced in chain Chlamydospore enlargement within the hypha segment Figure 12.1

Sexual reproduction Sexual spores– form after the fission of two haploid nuclei from opposite mating type cells of the same species Plasmogamy Haploid donor cell (+) nucleus penetrates cytoplasm of recipient cell (–) Karyogamy (+ ) and (–) nuclei fuse Zygote (2N) Meiosis Diploid nucleus produces haploid nuclei (sexual spores) (N) Sexual spores produced by fungi characterize the phyla

Sexual spores 1. Zygospore Fusion of haploid cells produces one zygospore 2. Ascospore Formed in a sac (ascus) 3. Basidiospore Formed externally on a pedestal (basidium) Figure 12.6

Zygomycota Conjugation fungi Type of hyphae - Coenocytic Asexual spores - Sporangiospores Sexual spores- zygospores. Rhizopus nigricans, Common bread mold – Mucor a genus of about 40 species molds commonly found in soil and on plant surfaces, as well as in rotten vegetable matter (Opportunistic, systemic mycoses)

The Life Cycle of a Zygomycota Figure 12.6

Ascomycota Type of hyphae - Septate Asexual spores - Conidiospores. Sexual spores – Ascospores (in a sac - sac fungi) Opportunistic pathogens Aspergillus (black house mold) -opportunistic, systemic mycosis Blastomyces dermatitidis, Histoplasma capsulatum (systemic mycoses) Microsporum, Trichophyton (cutaneous mycoses) Saccharomyces (bread and beer yeast) Soy sauce production – fermenting soy beans

The Life Cycle of an Ascomycota Yeast comes in two mating types—"a" and “α” (alpha) - haploid Or as slightly larger diploid cell that carries both "a" and “α” Spore formation Under high stress conditions, haploid cells will generally die; When diploid cell runs out of food, undergo sporulation - entering sexual reproduction (meiosis) and producing a variety of haploid spores of the two different mating types, Spores remain enclosed in a tough shell until times improve. Then these spores burst forth and start looking for mates of the opposite type; as soon as they find a suitable mate, they fuse (conjugate) together. Saccharomyces life cycle

Basidiomycota Type of hyphae - Septate. Asexual spores - Conidiospores. Sexual spores - Basidiospores Cryptococcus neoformans (systematic mycosis) often found in soil which has been contaminated by bird excrements lung infection fungal meningitis

The Life Cycle of a Basidiomycota Figure 12.8

Anamorphic fungi Teleomorphic fungi - Produce sexual and asexual spores. Anamorphic fungi - Produce asexual spores only. rRNA sequencing places most in Ascomycota, a few are Basidiomycota Penicillium (green fruit mold) Sporothrix (subcutaneous mycosis) Stachybotrys, Coccidioides, Pneumocystis (systemic mycoses) Candida albicans (Cutaneous mycoses)

Fungi Identification Physical appearance Colony characteristics Reproductive spores Fungi differ from bacteria: Like acidic environments (pH 5) Resistant to osmotic pressure Grow in low moisture Require less nitrogen Can metabolize complex carbohydrates Table 12.1

Lichens Mutualistic combination of Fungus and a Photosynthesizing partner Fungus provides holdfast Photosynthesizing partner - Alga or Cyanobacteria -, produces and secretes carbohydrates Lichens colonize habitats that are unsuitable for either the alga or the fungus alone. Lichens may be classified on the basis of morphology as crustose, foliose, or fruticose. Lichens are used for their pigments and as air quality indicators.

Economic Effects of Fungi Ecological Role: decomposing organic matter; indispensable in nutrient cycling and exchange Some human and plant pathogens Some spoil food Biothechnology Food and beverage production Antibiotics Vaccine production Biological control of pests - entomopathogenic fungi

Fungal Diseases (mycoses) Fungal infections classified on the degree of tissue involvement and mode of entry into the host: Superficial mycoses - localized to the skin, the hair, and the nails. Cutaneous mycoses (dermatomycoses) - affect hair, skin, nails Subcutaneous mycoses - beneath the skin Systemic mycoses - deep within body Opportunistic mycoses - caused by normal microbiota or fungi that are normally not pathogenic

Learning objectives List the defining characteristics of fungi. Differentiate between sexual and asexual reproduction, and describe each of these processes in fungi. List the defining characteristics of the three phyla of fungi Identify beneficial and harmful effects of fungi. Describe the roles of the fungus and the alga in a lichen.