Fungi Biology PDF

Fungi  Learning Outcomes To understand the basic cell biology of fungi. To understand the differences between the two main types of fungi, and their respective reproduction cycles. To provide examples of different fungi in relation to their habitat....

Fungi  Learning Outcomes To understand the basic cell biology of fungi. To understand the differences between the two main types of fungi, and their respective reproduction cycles. To provide examples of different fungi in relation to their habitat. Armillaria solidipes, Smithsonian  Fungi Fungi are eukaryotic, multicellular organisms. Growth varies between species; it can be through budding in yeast, or through the production of hyphum or spores, which can be spread over long distances. Britannica “In 1998 a team from the US Forest Service set out to investigate the cause of large tree die-offs in the Malheur National Forest in east Oregon.” BBC University of Utah  “Tree-killing” fungi! “They identified affected areas in aerial photographs and collected root samples from 112 dead and dying trees, mostly firs. Tests showed all but four of the trees had been infected with the honey fungus Armillaria solidipes. By observing which ones fused and which ones rejected each other, they found that 61 of the trees had been struck down by the same clonal colony – individuals with identical genetic make-up that all BBC originated from one organism.” Armillaria solidipes, Smithsonian  Armillaria solidipes largest living mushroom The largest was found in Oregon, America, and measures 2.4 miles across!  Infectious fungi of humans Perhaps the most well-known fungus that causes human disease is Candida albicans. This yeast-like fungus causes thrush in humans, well as gastro-intestinal disease. C. albicans is a commensal fungus, which is part of the normal flora of the body. This means that it is usually present, but will cause disease if there is an imbalance in host biochemistry, or another infection is present, for example. Exodontia CDC  Lichens University of Maryland Royal Botanic Gardens, Edinburgh Chytridiomycosis in frog Fungal growth on skin  Pathogenesis of chytridiomycetes Batrachochytridium dendrobatidis Affects frogs world wide. Fungal spores come in to contact with susceptible skin. Possibly spread via South African clawed toads which were used in pregnancy testing. This frog is not affected by the fungus, but many other species are. May kill up to 80% of population of some frog species!  Overview of Fungal Classification  Fungal classification In general, fungi are classified into one of two types – Yeasts – Filamentous Filamentous species, Yeast species, Saccharomyces cerevisiae Phanerochaete chrysosporium Some examples of commonly encountered fungi in our daily lives & the environment.  Examples of filamentous fungi associated with food-borne disease Example: Mucor sp = bread mould Example: Phytophthora infestans = potato blight  Edible Fungi? Mushrooms Group: Basidiomycetes Edible example: Agaricus spp. = edible mushroom Agaricus blazei https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/agaric  Edible Fungi? Non-edible example: Entaloma sinuatum = poisonous firstnature Example of a yeast species of fungus (Alberts, 2008) Group: Ascomycetes Example: Saccharomyces cerevisiae = baker’s yeast and brewer’s yeast  Example of a filamentous species of fungus & human infectious disease University of Adelaide Deuteromycetes Examples: Trychophyton spp. Fungal Nutrition  Fungal Nutrition A large number of fungi act to break down dead organic matter to act as a source of food: i.e. fungi are saprophytic (saprophytes) – e.g. mushrooms Many are parasitic: they obtain nutrients from living organisms- e.g. pathogens such as Trichphyton species causing athlete’s foot.  Saprophytes Fungi are the principle decomposers in every ecosystem. They can break down most organic compounds including lignin, a compound that is a major component of wood and is very difficult to break down or digest. Key Gardens Laetiporus sulphureus  Phanerochaete chrysosporium This environmental fungus produces the extracellular enzyme ligninase. Researchgate  Lignin degradation by fungi The composition of lignin varies between species of plant. However, it accounts for approximately 10-30% of cellulose related materials, and therefore represents a large amount of biological resource, in terms of available food. Phanerochaete chrysosporium is a white-rot fungus capable of breaking down this substance. Researchgate  Lignin degradation by fungi Phanerochaete sp. have only been recovered from environmental samples for analysis a relatively few number of times. Therefore, information on abundance is rather limited. Picture In the image, the white material (sometimes known as a “cobweb” appearance) is actually a mass of meiotic spores lying on top of the main fungal body on the plant (tree) surface. woodwildpark  Factors affecting lignin degradation Conditions which favour the growth of white-rot fungi, including adequate nitrogen, moisture, and temperature, all appear to be important in encouraging lignin decomposition. 5 to 11% increase in anaerobic digestability of barley straw has been noted after 3 to 4 week aerobic incubations at 30°C with white-rot fungal species. Therefore, the importance of the environment must be noted when observing this organism (the conditions within host animal tissues is also important for parasitic fungi.)  Fungal Nutrition: parasitism Parasitic fungi are those which cause infectious disease. All pathogenic organisms express virulence factors which facilitate one or more aspect of a disease. These can be detected by DNA analysis (e.g. PCR) and can be ‘typed’. What sort of samples do you think we can use to ‘type’ a fungal pathogen?  Plant-fungi interactions Some fungi can live within plants as endophytes. These fungi grow between the plant cortex cells to cause disease. Not all associations are disadvantageous. Some fungi produce alkaloids, which can enter the plant sap and make it resistant to insect predation.  Plant-fungi interactions It has been shown that infection of plants by Gymnosporangium asiaticum alters the metabolism of the plant, leading to a decrease in the available sugars within the plant host itself. This has been suggested to be responsible for dampening down plant metabolism in terms of cell wall synthesis and lesion repair, which could exacerbate the infection. This is an example of host-pathogen interactions, but within a plant, not an animal. Nature.com Yeasts  Candida albicans The microscopy image shows the larger yeast cells, with the arrows indicating buds. researchgate  Candida sp Candida sp are yeasts which reproduce by budding C. albicans is an opportunistic pathogen. Meaning that if conditions are favourable, then it will be able to manifest disease. Otherwise, it exists as a commensal organism. Most common manifestations are ‘thrush’ and sometimes oral Candidiasis.  Candida albicans C. albicans is a yeast type of fungus, meaning that it reproduces by budding. It is a commensal member of the normal microbiota of humans, and can cause incidents of disease. “Candida yeasts normally reside in the intestinal tract and can be found on mucous membranes and skin without causing infection; however, overgrowth of these organisms can cause symptoms to develop.” CDC Oral candidiasis www.thachers.org Basic yeast cell anatomy Sciencedirect.com  Reproduction in yeast Yeast reproduce by budding. This is a vegetative out-growth where the daughter cell is similar, but smaller, than that of the parent. researchgate  Yeast life cycle 4 5 6 3 7 2 1 Filamentous Fungi Trichophyton rubrum spore hyphum University of Adelaide  Athlete’s foot (caused by Trychophyton rubrum) Australasian College of Dermatologists  Fungal anatomy: Hyphum Filamentous fungal growth is is achieved through the production of a mycelium, which consists of numerous hyphum. Hyphum are long cylindrical-like structures that constitute many individual cells joined together. mitochondrion vacuole nucleus cell wall septa (former cell wall between individual cells)  Hyphum & Mycelia vacuole nucleus mitochondrion cell wall septa Mycellium Hyphum  Unicellular spores Multicellular hyphum  Aspergillus fumigatus Conidia A = conidia A B = hyphum & mycelia (main body of the fungus) These type of fungus are also referred to either filamentous fungi or molds. B  Fruiting bodies These are large structures that are very similar to those found on the underside of the head of mushrooms. They are designed to disseminate spores on the wind, or by contact with passing animals. They originate from hyphum coming through the plant tissue of the tree, and breaking through the bark. Reproduction: filamentous fungi 5 6 4 7 3 2 1  “Zombie fungi” – headline-grabbing! Scientificamerican “Cordyceps” fungi have been identified in numerous parts of the world, such as South East Asia, as being responsible for modifying the behaviour of their animal hosts.  “Zombie fungi” The ability of the fungus to alter behaviour of the host insect is remarkable. It has been suggested as an extreme example of natural selection. “A striking example of a parasite's extended phenotype are diverse fungi that cause insects to die while attached to leaves. This death grip behavior functions to secure the insects in an ideal location for spore dispersal from the fruiting body that sprouts from the dead insects.” Electron microscope images of animal-plant-fungi interactions  “Zombie fungi” https://www.youtube.com/watch?v=XuKjBIBBAL8  Summary Points Fungi are EUKARYOTIC – same basic anatomy as animal & plant cells, but with some unique features (e.g. cell wall composition). There are two main types (yeasts and filamentous); each has its own unique reproduction cycle, which you need to know. The two types of fungal nutrition are: – Saprophytic & parasitic – Learn examples of species in relation to specific habitats relevant to course discipline.  Further Reading Brock Biology of Microorganisms – Chapter 18 (page 635) Pepper et al. Environmental Microbiology – Chapter 2.3 (page 39)