CAS BI 108 Lecture Notes - Lecture 3: Dimorphic Fungus, Hypha, Mycorrhiza

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11 Nov 2016

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Ecologically and economically important because: nosocomial infections, plant pathogens, food chain/decomposers, digestion, medicine, food and produce food, plant symbiots = the mycorrhizae. Mushroom = temporary above ground reproductive structure: pilus (stalk, cap, gills. Similarities: grow in ground, sessile, have a cell wall. Differences: cell wall made of chitin, lack chloroplasts. Life cycle of a fungus: haploid phase. Start with haploid spores formed by meiosis. Spores germinate and grow into haploid mycelia. Cells haploid, undergo mitosis to form fungal body. Fusion of two mating types, exchange of nuclei. Terminal cells of hyphae become sporangia (pair of haploid nuclei) Two haploid nuclei fuse to finally become zygote. Zygotes form in specialized cells on underside of cap called sporangia (sporangium) Zygotes undergo meiosis in sporangia to produce haploid spores. Fungi are classified into 3 basic groups based on reproduction: zygomycota (ex. Coprinus: deuteromycota = the false fungi, most pathogenic.

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Fungi Fungi are the great decomposers of the biosphere. Most plants form mycorrhizae with fungi to increase absorptive area without having to grow more roots, in this relationship fungi recieve carbohydrates from plants. Humans consume fungi, mushrooms, may use fungi as a source of drugs for blood pressure, antibiotics and immunosuppresive drugs. Fungi are used in biotechnology to produce fermetation products, and some have been very useful models to study gentics in eukaryotic cells that are unicellular such as yeasts. About one third of fungi may cause infections, mycoses, in plants, animals and humans. Fungi tolerate concentration of salt and sugar that plasmolyze bacteria in perserved foods exposed to air which contains fungal spores may germinate and may spoil food. Fungi have two body shapes, molds and yeasts. Mold are large and made of long filamentous hyphae. Hyphae form mats called mycelium ( plural is mycelia). Mycelia may extend for miles underground, making fungi the largest organism on earth. The visible portion of subterrean fungi are the fruitng bodies such as mushrooms. Yeasts are globular and unicellular. They may bud forming up 24 daughter cells from a single cell. When budding is incomplete it may produce a psuedohypa. Fungi that may exist in both body types are dimorphic fungi. In general, the yeast form of a dimorphic fungus is a pathogen, the filamentous form is not pathogenic. Examples are Histoplasmosis capsulatum (histoplasmosis) and Coccidiodes immitis (coccidioidomycosis). Fungi are saprobes, they absorb nutrients from the remains of dead plants or they lasso nematodes. Fungi may derive nutrients from a living plant utilizing haustoria which are modified hyphae that penetrate living plant tissue. Some fungi use melanin to absorb gamma rays which they convert to chemical energy. Some herbivores have fungi in thier gut microbiome to help digest plants. Zygomycota contains 1100 species and reproduces asexually through sporangiaspores, which form in a sac called a sporangium on a stalk called a sporangiaphore. An example is Nosema which is an obligate intracellular parasite in insects and honeybees. Ascomycota havd 32,000 species form haploid ascospores in sacs called ascus (asci plura) and reproduce asexually with condiospores which develop on the tips of hyphae on stalks called conidiophores. Examples are Claviceps purpurea, ergot, which grows on grain and causes abortions in cattle and hallucinations in humans. Penicillium the source of the first antibiotic discovered by Fleming in the 1940s. Saccharomyces, a facultative anaerobe, ferments sugar to produce alcohol and carbon dioxide gas and is used in baking and brewing. Neurospora was used as a model to study molecular biology, Beadle and Tatum established one gene one enzyme using this model organism.

14. Why are there more antibacterial drugs than antifungal drugs? Basidiomycota have fruiting bodies called basidiocarps. Basidiospores are dispersed by the wind and germinate in warm moist environments. An example is the pathogen Cryptococcus neoformans the leading cause of fungal meningitis

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CAS BI 108 Lecture Notes - Lecture 3: Dimorphic Fungus, Hypha, Mycorrhiza

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