Introduction to Fungi SHES2250
Introduction to Fungi
Mycology Subdiscipline of botany; ICBN eg. Penicillium, Neurospora, Saccharomyces Heterotrophic absorptive eukaryotes; nonphotosysnthetic cell wall contains chitin; produce spores Tight phylogenetic cluster Saprophytes, parasites - enzymes
> 100,000 spp.; size range: unicellular microscopic yeasts multicellular(filamentous) molds, mushrooms Habitat: soil, freshwater, marine Body of fungus = thallus Thallus of most multicellular fungi mycelium; hyphae Contains some of the most important organisms, in terms of their roles in ecology, economy, health and science
Hyphal cells contain 1 or 2 nuclei; separated by septa Septalpore: woroninbody Cell walls: 80-90% polysaccharide, protein, lipids-sterols, etc. Chemoorganotrphs Low pH, high temperature tolerant-ubiquitous Common contaminant of food products, microbial culture media and surfaces cell interiors may be connected by septa (septated) or coenocytic
Hyphae
The part of the fungus that feeds, grows, and ultimately may produce a mushroom or some other kind of reproductive structure. Morphology: cobwebby strands of subterranean white stuff. absorb nutrients: sugars, amino acids, nucleic acids secrete digestive enzymes to break down large molecules Once the hyphae attain a certain maturity and if surrounding conditions are right, very complex changes occur inside the hyphae, and their many-shaped, manycolored, interesting reproductive structures may be formed
All growth activity in filamentous fungi results in elongation of hyphae, the growth is unidimensional. Branches, once formed, elongate. Three dimensional structures consist of hyphae that are glued together by mucilage, and physically bound by specialised hyphae. Development is a dynamic process. Hyphae branch and in culture, the resultant mycelia consists of hyphae growing away from other hyphae. It is suggested that this results in a thorough exploration of the substrate maximising utilisation of the nutrients
Strands arise when hyphae grow in parallel. Both hyphae can continue to branch and aggregate Rhizomorphs are highly organised strands. The rhizomorph of Armillariamellea has an apical growing point. Cells of the outer layer of the rhizomorph are thickwalled, tightly packed, and walls melanised. Cells of the central region are thin walled. The entire rhizomorph is covered by fine hyphae which radiate out into the soil, and resemble the root hairs of a root.
When strands erect above the substrate, they may then form conidia on the termini. These structures are called synnemata, and the conidia are commonly present in mucilage. Thus the effect of the erect conidiophores is to present spores to passing arthropods for dispersal. Stalks of the fruiting body of agarics consist of parallel hyphae bound by fibre hyphae. Thus they are similar to erect rhizomorphs. They also have a dispersive function, and thus are similar to synnemata.
The sclerotia are organised structures. Sclerotia are initiated with hyphae aggregated into small knots within the mycelialmass. The knot increases in size and hyphae in the centre accumulate reserves from the connected mycelium. As the sclerotia increases in size, cells of the outer layer becomes melanised, and thick walled. These also become vacuolated, and eventually collapse, providing a protective layer over the surface. The giant sclerotia of Polyporus spp. is honeycombed by large cells which transparent material, thought to be a water reserve The process of development of complex structures is governed by genetic controls.
Reproduction: asexual, sexual Asexual-budding Sexual-haploid gametes unite-plasmogamy If nuclei fail to unite dikaryotic cells Nuclei fuse-karyogamy diploid cell Spores: asexual, sexual Motile spores-aquatic fungi; thick protective spores-terrestrial fungi Germinating spores single cells or germ tubes Dimorphism
Cultivation and Preservation
Isolation media-Potato dextrose agar, water agar, etc. Culture media-Sabourauds agar, Czapeks agar, etc. Culture condition: pH acidic temperature: Dermatophytes, mycoses-causing, psychrophilic, thermophilic
Preservation Serial transfer-agar slant Mineral oil Water storage Sterile soil/ sand Silica gel Freezing Drying on organic substrates/ paper Freeze-drying
