Fungi, once considered plant-like organisms, are more closely related to animals than plants. Fungi are not capable of photosynthesis: they are heterotrophic because they use complex organic compounds as sources of energy and carbon. Some fungal organisms multiply only asexually, whereas others undergo both asexual reproduction and sexual reproduction with alternation of generations.
Most fungi produce a large number of spores, which are haploid cells that can undergo mitosis to form multicellular, haploid individuals. Like bacteria, fungi play an essential role in ecosystems because they are decomposers and participate in the cycling of nutrients by breaking down organic and inorganic materials to simple molecules. Fungi often interact with other organisms, forming beneficial or mutualistic associations. For example most terrestrial plants form symbiotic relationships with fungi.
The roots of the plant connect with the underground parts of the fungus forming mycorrhizae. Through mycorrhizae, the fungus and plant exchange nutrients and water, greatly aiding the survival of both species Alternatively, lichens are an association between a fungus and its photosynthetic partner usually an alga. Fungi also cause serious infections in plants and animals.
For example, Dutch elm disease, which is caused by the fungus Ophiostoma ulmi , is a particularly devastating type of fungal infestation that destroys many native species of elm Ulmus sp.
The elm bark beetle acts as a vector, transmitting the disease from tree to tree. Accidentally introduced in the s, the fungus decimated elm trees across the continent.
Many European and Asiatic elms are less susceptible to Dutch elm disease than American elms. In humans, fungal infections are generally considered challenging to treat. Unlike bacteria, fungi do not respond to traditional antibiotic therapy because they are eukaryotes.
Fungal infections may prove deadly for individuals with compromised immune systems. Fungi have many commercial applications. The food industry uses yeasts in baking, brewing, and cheese and wine making. Many industrial compounds are byproducts of fungal fermentation. Fungi are the source of many commercial enzymes and antibiotics. Fungi are unicellular or multicellular thick-cell-walled heterotroph decomposers that eat decaying matter and make tangles of filaments.
Fungi are eukaryotes and have a complex cellular organization. As eukaryotes, fungal cells contain a membrane-bound nucleus where the DNA is wrapped around histone proteins. A few types of fungi have structures comparable to bacterial plasmids loops of DNA. Fungal cells also contain mitochondria and a complex system of internal membranes, including the endoplasmic reticulum and Golgi apparatus. Unlike plant cells, fungal cells do not have chloroplasts or chlorophyll. Many fungi display bright colors arising from other cellular pigments, ranging from red to green to black.
The poisonous Amanita muscaria fly agaric is recognizable by its bright red cap with white patches. Pigments in fungi are associated with the cell wall. They play a protective role against ultraviolet radiation and can be toxic.
The poisonous Amanita muscaria : The poisonous Amanita muscaria is native to temperate and boreal regions of North America. The rigid layers of fungal cell walls contain complex polysaccharides called chitin and glucans. Chitin, also found in the exoskeleton of insects, gives structural strength to the cell walls of fungi. The wall protects the cell from desiccation and predators.
Next time you go walking in a forest during the summer months, take a look up and see if you can spot any branches missing their leaves. Homepage Why Microbiology Matters What is microbiology? Fungi Fungi can be single celled or very complex multicellular organisms. They are found in just about any habitat but most live on the land, mainly in soil or on plant material rather than in sea or fresh water.
A group called the decomposers grow in the soil or on dead plant matter where they play an important role in the cycling of carbon and other elements. Some are parasites of plants causing diseases such as mildews, rusts, scabs or canker. In crops fungal diseases can lead to significant monetary loss for the farmer. A very small number of fungi cause diseases in animals. Observing fungi in a Petri dish Educational resource for students: Observing fungal cultures in a Petri dish and learning about colony morphology.
Fungal diseases Fungal diseases can have a devastating effect on our health and our environment. The spores grow in special structures called sporangia on gills on the underside of the cap and they burst periodically.
The spores are released and dispersed by air currents, germinating if they land on a suitable food source. Go to www. Mushrooms keep best if they are stored free from moisture in cool conditions.
They are often sold packaged under plastic film where the reduced oxygen level increases shelf life. Cultivated mushrooms are usually cooked, which kills any harmful bacteria that may have contaminated them from soil, insect pests, rodents or handling during processing. The greatest risks are from faecal bacteria, Staphylococcus aureus and bacterial spores from the soil. However commercial mushroom production is carried out with great attention to hygiene and there have been few reported cases of food poisoning from this product.
Mushrooms are filamentous fungi that produce large, often edible fruiting bodies. They live on organic material, thriving on compost, fallen leaves and damp wood and any other dead plant or animal matter.
If the pasteurization starts with only , microbes only about , will survive. Fewer microbes will take a longer to multiply and reach the maximum population delaying the conversion of ammonia to mushroom food after pasteurization.
An effective pasteurization will eradicate harmful bacteria, nematodes, insects and fungi. Growers may make several compromises to this recommendation. Unless all the compost substrate surfaces and areas are exposed to this temperature range some destructive organisms may survive causing problems later in the crop.
Sometimes it is necessary to have a high override because the cross over time is lengthen to insure inconsistent compost substrate is properly pasteurized. The compromise with a high override temperature is that it will take longer to convert ammonia to protein after the pasteurization, because more good microbes are killed or inactivated.
To illustrate this concept we will consider the earlier example however we start pasteurization with the same number of microbes, e. Therefore it takes less time for the population to reach the maximum growth phase and the conversion of ammonia and carbohydrates continue at a faster rate. This is not to suggest to use a shorter crossover time to lower the override and reducing the kill during pasteurization to speed up conditioning.
The idea is to be prepared to handle the post-pasteurization more carefully after a higher override. After pasteurization many microbes have been killed or inactivated and they need to recover. A longer recovery time for the microbial activity causes compost substrate to have less heating ability immediately after pasteurization.
It is at this stage that the compost substrate may want to drop faster or go to low. Since fewer microbes are growing less oxygen is required and very little ventilation or fresh air is needed at this stage. Maintaining a flame in a Phase II room indicates there is enough oxygen in the room air. A slight tendency for the compost substrate temperature to rise indicates that the microbes are recovering and more activity is anticipated.
More oxygen may be needed and a little more ventilation will be required. Since less food is available at this stage than before pasteurization less ventilation is required for the remaining part of Phase II.
The longer the microbes in the compost substrate remain in this range with all the critical growth requirements available the faster the ammonia will be converted. The process of going through this temperature range will produce the most protein or the maximum amount of food for the mushroom.
Of course reality is different. There are many situations that arise where growers have to compromise Phase II management. Compromises are usually made when over or under composted material, wet or dry compost, or any combination of these conditions occur.
Dry compost substrate will be difficult to control and there may not be enough moisture for the microbes at the end of the Phase II. Wet or over composted material may have trouble because there is a lack of air or carbohydrates for the microbes to grow. Short compost substrate or too many compost substrate fines or balls are difficult areas to condition properly.
Some of the beneficial microbes growing during Phase II use other types of food besides ammonia. If this non-ammonia type food is left over competitor molds or weed molds may use these readily available compounds to grow and develop.
Not only may these undesirable molds be a concern it also means there is less food available for the mushroom. Near the completion of the phase II check for ammonia in the compost. The nose is usually the best tool, however there are ammonia testing kits and strips are available to supplement the nose test.
Once the next medium temperature compost substrate is near the lowest conditioning range, check that compost substrate before cooling any further. The warmest areas of the room may clear last and it is important to make sure those areas spend time in the lower temperature range.
The two main types of microbes found in compost substrate during Phase II are thermophilic fungi and actinomycetes. Their names are not as important as the way they grow. The actinomycetes generally prefer the higher temperature ranges. Their colonies of millions of individual cells or fragments appear as the white specs that some growers refer to as "firefang" or "flecking. They do not spread out and usually only grow where they are first originate with suitable food, water and temperature.
The thermophilic fungi are more thread-like. They have mycelium that looks similar to mushroom spawn growth so they are able to grow in a direction of the food or towards more favorable growing conditions.
They are able to penetrate the dense parts of the compost, such as fines or balls found in compost substrate that is excessively decomposed or too short. The plant-soil system can be used to explain the importance of growing different microbes during Phase II. When a plant root grows through soil the root is able to absorb food or nutrients from a distance away from the root surface. Roots obtain these nutrients by absorbing water and the nutrients dissolved in that water.
This water is called the soil solution. As the water and nutrients are adsorbed by the root a gradient is created which draws more water and food towards the root. Compost substrate is a complex material that microbes and the mushroom obtain their food and water. The soil is much more simple system than the rich decaying matter the mushroom extracts its food. Unlike the relatively simple plant-soil system, how the mushroom obtains its food and water from compost substrate is an unknown, yet probably similar, process.
How much of the root or mycelium is absorbing the nutrient is depends on a number of other factors. However, for this illustration we can assume most of the surface area of the microbe is able to absorb nutrients.
Let's consider the region a microbe may adsorb food may be called "area of conversion. Thermophilic fungi have a larger area of conversion because of the way they can grow through the dense compost substrate as a fine thread of mycelium.
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