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=Introduction=
=Introduction=
Although there are over 50,000 identified species of fungi, only a few hundred are known to be pathogenic, causing infections known as '''mycoses''' (mycology being the study of fungi). Fungi are nonphotosynthetic organisms which are restricted to a parasitic or saphrophytic exsistence. They are abundant in soil, vegetation, water and on decaying vegetation and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts).
Although there are over 50,000 identified species of fungi, only a few hundred are known to be pathogenic, causing infections known as '''mycoses''' (mycology being the study of fungi). Fungi are nonphotosynthetic organisms (lack chlorophyll) which are restricted to a parasitic or saphrophytic exsistence. They are abundant in soil, vegetation, water and on decaying vegetation and wood. Fungi have a eukaryotic cell structure and are able to grow as branching or filamentous forms (mycelia) or as single cells (yeasts).
=Structure=
Fungi are surrounded by a multi-laminate fibrous cell wall which provides rigidity, shape, determines the cellular volume and enables the cell to maintain turgor. The cell wall is composed of polysaccharides and carbohydrates (chitin and cellulose).
Inside the cell wall lies the thin, cytoplasmic cell membrane. The cell membrane is composed of lipid and protein and regulates the passage of substances into and out of the cell, such as metabolites and waste products. Important metabolites are taken up by active transport as the cell membrane is relatively impermeable. The cell membrane is also the first barrier to toxic materials entering the cell and is important in degredation of extra-cellular nutrients.
Reserve materials such as fats, glycogen and protein are stored as granules in the cytoplasm. As the cell ages, vacuoles appear which also contain reserves of metabolites and provide turgor to help keep the cell's shape and are important in growth of the organism.
=Types of Fungi=
=Types of Fungi=
There are two principle types of fungi, the moulds and the yeasts. Fungal '''hyphae''' are the branching tubular structures of moulds which become entwined as the fungi grows to form a '''mycelium'''. Hyphae are divided by cross walls into '''septa'''. There are arial (above the surface) and surface hyphae. The aerial hyphae produce spores which are reproductive fungal cells. There are two main types of spore produced, '''conidiospores''' and '''sporangiospores'''. These produce asexual spores called '''conidia''' which are relatively resistant to physical and chemical agents.
There are two principle types of fungi, the moulds and the yeasts. The moulds are further divided into filamentous or dimorphic fungi.
Filamentous fungal '''hyphae''' are the branching tubular structures of moulds which become entwined as the fungi grows to form a '''mycelium'''. Hyphae grow by apical elongation as new wall material is laid down constantly at the tips of the terminal and lateral branches. Septate hyphae are divided by cross walls into '''septa'''. Each septum has a small central pore (dolipore) maintaining protoplasmic continuity throughout the hyphae allowing rapid nutrient transport and nuclear migration. Dead or damaged parts of septate hyphae are cut off by a plug blocking the septal pore. Non-septate hyphae only form cross walls to cut off dead or damaged parts of the hyphae and to delimit reproductive organs. There are arial (above the surface) and vegetative (surface) hyphae. The aerial hyphae produce spores which are reproductive fungal cells and vegetative mycelium have an assimilative function. There are two main types of spore produced, '''conidiospores''' and '''sporangiospores'''. These produce asexual spores called '''conidia''' which are relatively resistant to physical and chemical agents.
Dimorphic fungi develop as a mycelium or into another form depending on environmental conditions. There is usually as yeast like parasitic phase and a mycelial saprophytic phase. Dimorphic fungi show phenotypic duality and more than one physiological factors may be involved in dimorphic changes.
The yeasts range from 3µm to 5µm and are oval or spherical cells. '''Pseudohyphae''' are produced by some yeasts which are chains of irregular yeast cells. '''Dimorphic fungi''' change from the mycelial form into yeasts in certain conditions, e.g. 37°C or when inside animal tissue.
The yeasts range from 3µm to 5µm and are oval or spherical cells. '''Pseudohyphae''' are produced by some yeasts which are chains of irregular yeast cells. '''Dimorphic fungi''' change from the mycelial form into yeasts in certain conditions, e.g. 37°C or when inside animal tissue. Yeasts reproduce mainly by budding of the oval, unicellular or round thallus. The daughter cells may remain attach to the aprent yeast cells for several generations forming chains or colonies. To identify yeasts, the ability to assimilate sugar and nitrogen and the fermentation of various sugar compounds is studied.
=Fungal Reproduction=
=Fungal Reproduction=