Fungi - Overview
Introduction
Fungi are widely distributed throughout the environment and are eukaryotic non-photosynthetic heterotrophs that produce exoenzymes and obtain nutrients by absorption. Moulds and yeast represent the two main morphological types of fungi with multicellular moulds forming branching filaments called hyphae and unicellular yeasts having an oval or spherical appearence. Fungi grow aerobically and most are strict aerobes. Fungal reproduction can either be sexual or asexual and in some species both types can occur. Fungi are able to tolerate high osmotic pressures and acidic environments as low as pH 5. Most fungal species of veterinary importance are referred to as deuteromycetes although some pathogenic fungi do exist in other phyla.
Types of Fungi
Within the kindgom of Fungi there are four phyla; Ascomycota (ascomycetes), Basidiomycota (basidiomycetes) and Zygomycota (zygomycetes). These can be ditinguished by their sexual forms or telomorphs. Fungi imperfecti (deuteromycetes) do not have a sexual form and therefore represent a heterogenous fourth phyla.
Fungal species can be called saprophytic, parasitic or mutualistic. Mutualistic fungi have obligatory associations with microorganisms without which the fungi cannot complete it's own life cycle. Mutualistic fungi are non-pathogenic.
Fungal Structure
Hyphal cell walls formed by moulds provide the cell with a rigid structure that provides a high degree of protection against osmotic pressure. These hyphal cell walls are mainly composed of chitin and other polysaccharides. The cell wall of yeasts contains protein complexes with polysaccharides and in some species also lipids. In both species the cell wall is lined by a bilayered cell membrane. Yeasts and mould both have defined nuclei, nuclear membranes, mitochondria and networks of microtubules.
Growth and Reproduction
Fungal spores are able to germinate where environmental conditions are favourable. Fungal spores are the result of either sexual or asexual reproduction. When this occurs