Chapter 26 The Fungi (Eumycota)
Overview on Fungi are found wherever moisture, the appropriate temperature and suitable organic nutrients are present exist primarily as filamentous hyphae mycelium = a mass of hyphae fungi secrete exoenzymes to digest insoluble matter, then absorb the solubilized nutrients have two reproductive structures sporangia form asexual spores gametangia form sexual gametes
True fungi fungus (pl., fungi) eucaryotic spore-bearing chemoorganoheterotrophs with absorptive metabolism reproduce sexually and asexually belong to kingdom Fungi (Eumycota) within domain Eucarya
Some terms fungus mycology mycologists mycotoxicology mycoses eucaryotic organisms that are spore-bearing, have absorptive nutrition, lack chlorophyll and reproduce sexually and asexually mycology study of fungi mycologists scientists who study fungi mycotoxicology study of fungal toxins and their effects mycoses diseases caused by fungi
Distribution primarily terrestrial few aquatic species many are pathogenic in plants or animals some form associations mycorrhizae – associations with plant roots lichens – associations with algae or cyanobacteria
Importance beneficial impact detrimental impact decomposers industrial fermentations fermented foods and beverages steroids, antibiotics and other drugs research model eucaryotic organisms detrimental impact major cause of plant diseases cause of many animal, including human, diseases
Table 26.1
Structure thallus body or vegetative structure of a fungus cell walls usually composed of chitin polysaccharide consisting of N-acetyl glucosamine residues
Yeasts unicellular fungi reproduce asexually, often by budding reproduce sexually by formation of spores
For clarity, the plasma membrane has been drawn separated from the cell wall. In a living cell the plasma membrane adheres tightly to the cell wall. Figure 26.4
Molds filamentous fungi hyphae (s., hypha) mycelium (pl. mycelia) the filaments of a mold may be coenocytic (no cross walls) or have septa (cross walls) mycelium (pl. mycelia) bundles or tangled masses of hyphae
Figure 26.5
Figure 26.6
diagrammatic representation of hyphal tip Figure 26.7
Table 26.2
Dimorphism some fungi change from yeast form (Y) to mold form (M) YM shift in animals, Y in host and M outside host in plants, M in host and Y outside host
Nutrition and Metabolism most are saprophytes obtain nutrients from dead organic material secrete hydrolytic enzymes chemoorganoheterotrophs glycogen in primary storage polysaccharide most are aerobic some are facultative anaerobes obligate anaerobic fungi are found in rumen of cattle
Reproduction asexual reproduction sexual reproduction transverse fission budding spore production sexual reproduction involves union of compatible nuclei followed by formation of sexual spores (zygospores, ascospores, or basidiospores)
Figure 26.8
Sexual reproduction zygote formation several mechanisms fusion of gametes fusion of gametangia gamete-producing bodies fusion of hyphae
Sexual reproduction + and – Pheromones - proteins Two different strains + and – Pheromones - proteins Attract negative strain – mate + and - fuse to make zygote Differentiates into a sexual spore Environmental conditions Nutrient depletion
Zygomycota zygomycetes form coenocytic hyphae containing numerous haploid nuclei most are saprophytes a few are plant and animal parasites some of industrial importance foods, antibiotics and other drugs, meat tenderizer, and food coloring
Reproduction in Fungi Figure 26.10 A drawing of the generalized life cycle for fungi showing the alternation of haploid and diploid stages. Some fungal species do not pass through the dikaryotic stage. The asexual (haploid) stage is used to produce spores that aid in the dissemination of the species. The sexual (diploid) stage involves the formation of spores that survive adverse environmental conditions (e.g., cold, dryness, heat). Figure 26.10 Rhizopus nigricans – common bread mold
Ascomycota ascomycetes (sac fungi) considerable human impact during sexual reproduction produce ascus (pl., asci) containing haploid ascospores considerable human impact food spoilage and plant diseases edible mushrooms, and food and beverage production research can be filamentous or yeast form filamentous forms have septate hyphae and asexual reproduction by conidiospores
Figure 26.13
Life cycle of ascomycetes Life cycle of ascomycetes. Sexual reproduction involves the formation of asci and ascospores. With the ascus, karyogamy is followed by meiosis to produce the ascospores. This figure shows sexual reproduction and ascocarp morphology of a cup fungus. Figure 26.14 (a)
Life cycle of ascomycetes Life cycle of ascomycetes. Sexual reproduction involves the formation of asci and ascospores. With the ascus, karyogamy is followed by meiosis to produce the ascospores. This figure shows sexual reproduction and ascocarp morphology of a cup fungus. Figure 26.14 (b)
Basidiomycota basidiomycetes (club fungi) human impact during sexual reproduction form basidium human impact decomposers edible mushrooms pathogens of humans, other animals, and plants e.g., Cryptococcus neoformans – cryptococcosis systemic infection, primarily of lungs and central nervous system
Figure 26.15
Glomeromycota considered zygomycetes by some major importance as endomycorrhizal symbionts of vascular plants form intracellular associations within roots of almost all herbaceous plants and tropical trees Fungi delivers soil nutrients Plant provides carbohydrates
Claviceps purpurea Grows on grains – rye Toxin – ergot Ergotism Hallucination Constriction of the capillaries – gangrene Middle ages
Figure 24.10 Hard mass of hypha Ergot of Rye