Lecture 3. The fungal cell - II

Transcription

1 Lecture 3 The fungal cell - II Asexual reproduction - formation of conidiospores (mitotic spores) Typical of Ascomycota Induction / suppression of conidiogenesis is controlled by both genetic and environmental factors.

2 Asexual reproduction - formation of conidiospores (mitotic spores) Typical of Ascomycota From Kendrick BLASTIC THALLIC Asexual reproduction - formation of conidiospores (mitotic spores) Diversity of forms in the Ascomycota ==> taxonomic distinction - Conidiophore - Conidium / conidia - Phialide arthrospores: resulting from hyphal fragmentation; usually produced in chains; e.g., Geotrichum

3 Asexual reproduction chlamydospores Chlamydospore: a chlamydospore is a thick-walled mitotic spore; it generally acts as a resting spore (dormancy before germination) Chlamydospores formed by the mycelium in culture of Fusarium oxysporum ( Chlamydospore formed by hyphae in the gills of the mushroom Nyctalis parasitica (left) and N. asterophora (right) (from J. Beck; cemachampi.blogs.sudouest.fr/) Chlamydospores and arthrospores can be produced by members of both Ascomycota and Basidiomycota. Asexual reproduction - formation of sporangiophores that contain mitotic spores Typical of Zygomycota

4 Important definitions and concepts: Anamorph: the asexual state in the life cycle of a fungus. Teleomorph: the sexual state in the life cycle of a fungus Holomorph: the whole fungus, anamorph + teleomorph Cell secretion, uptake of nutriments, and release of metabolites and other metabolites preparation of the environment for further growth; recognition systems C, N, H20, minerals, amino acids, etc... Decay or organic debris, etc. The stomach of a fungus is outside itself!

5 Nutrient requirements - Carbon source - Nitrogen source --- fungi do not assimilate atmospheric N but can use many other simple and abundant source of N, including nitrates (NO3), amino-acids (e.g., asparagine), ammonium, urea, etc. - Traces of mineral nutriments, in particular phosphorus (production of ATP) and iron ==> Simple culture media suffice for the cultivation of many fungi, e.g.: - Malt extract agar (MA) - Potato dextrose agar (PDA) - Yeast extract agar Liquid media: as above but without agar but many fungi cannot be cultured in these simple media. and there are still many fungi that humans have still not been able to cultivate (or domesticate!) These include - most obligate symbiotic and parasitic species. - they are called obligate biotrophic Fungi use a broad range of carbon substrate

6 Hyphal trophism to food sources Kinetics of fungal growth

7 Temperature and fungal growth - Examples Thermophiles Mesophiles Psychrophiles ph and fungal growth - Examples

8 Hyphal differentiation to facilitate transport or storage or nutriments Mycelial cords and rhizomorphs are vegetative hyphal formation for transport of nutrients, generally across nutrient free environments (they facilitate the spread of a fungus individual to a new site). They are quite common in wood rotting fungi(e.g., for a root pathogens to spread from root to root) and often present in mycorrhizal fungi. Mycelial cords have simpler morphology than rhizomorphs. Rhizomorphs often have a tick, black (melanized) external cell layer, and a lumen (= hole in the center). Sclerotia:hyphal bodies specialized in dormant survival; usually dense; can be very large in some Basidiomycetes (several cm across, e.g., in Pleurotus tuberregium). Are produced for instance in the plant pathogens Sclerotina spp., in the ergot fungus Claviceps purpurea, and in both some mycorrhizal and saprophytes Basidiomycota. Sclerotia of Sclerotina sp., From Kendrick; /CHAP4b.htm Sclerotia of Lignosus rhinocerus; / pages/ Mycelial cords and rhizomorphs are common in wood or litter decaying fungi From Clemencon, 1977 Anatomy of Hymenomycetes

9 Hyphal differentiation in the mycelial cord of Serpula lacrymans Mycelial cords of Serpula similis growing underneath a decaying fallen trunk From Clemencon, 1977 Anatomy of Hymenomycetes ca. 5 cm - dry rot of wood - cords can spreads several meters, including across plaster and brick walls in buildings!

10 Armillaria Smith, M., J. Bruhn and J. Anderson, The fungus Armillaria bulbosa is among the largest and oldest living organisms. Nature 356: Read more at apr2002.html

11 Secondary metabolites of ecological and human importance; examples Muscarin Amanita muscaria nausea, vomiting, hallucinations Phallotoxins A. virosa, A. phalloides liver damage and often death Psilocybin Psilocybe spp., Inocybe spp., Panaeolus spp. hallucinations Cyclosporin Trichoderma polysporum immunosuppressant to prevent organ rejection in transplant - Enzymes --- Amylases: starch conversions --- Pectinases: clarification of fruit juices --- Lipases: dairy products, detergents --- Phenol-oxydases, laccases: lignin degradation (applications in the paper industry) ---> food processing,flavoring; e.g., Penicillium roquefortii, P. camembertii (cheese), Rhizopus oligosporus (covert soybean to tempeh in Indonesian dishes, etc. Taxonomic notes: Oomycota are not Fungi Number of known species ca. 2,000 ca. 32,000 ca. 30,000 ca. 16,000 Deuteromycota is an artificial taxonomic groups for asexual stages (mostly for Ascomycota anamorphs) Many more antibiotic from fungal origin are known today, however, the taxonomic distribution pattern remains the same: Ascomycota anamorphs >> Basidiomycota >> Ascomycota teleomorphs