Fungi are primitive plants which do not utilize photosynthesis, are capable of anaerobic growth, and draw nutrition from decaying vegetable matter. This last feature allows fungi to use hydrolytic enzymes to break down biopolymers and recycle nutrients through the ecosystem. Unlike other organisms, fungi use exoenzymes to digest their food before ingesting it. Fungi do not have stomachs; they live in their food. More than 70,000 species of fungi have been discovered, and scientists estimate that perhaps around 1.5 million species of fungi exist. In an environment that lacks adequate nutrients, most fungi form spores to survive in the soil. The spore formation is operationally significant and allows fungi to be stable, storable, and easily aerosolized.
Fungi are eukaryotic, non-vascular organisms. Typically, fungi are non-motile organisms, but several exceptions, such as chytrids, have motile phases. Fungi are characterized by a cell wall made of chitin rather than the cellulose, the material that make up plant cell walls. Most fungi have a life cycle that includes either sexual (meiotic) or asexual (mitotic) reproduction through the dissemination of spores by wind. In asexual reproduction, the spores are formed in the aerial mycelium, and in sexual reproduction, spores are the result of fusion of two cells and their nuclei. The wheat rust fungus spores have been discovered up to 4000 meters in the air and up to 900 miles away. On average, fungi have small nuclei with little repetitive DNA, and during mitosis, fungi's nuclear envelopes do not dissolve.
Types of Fungi
There are three categories of fungi based on how they acquire their food: saprophytes, parasites, and mutualists. Saprophytes feed on non-living material and recycle carbon, nitrogen, and mineral in the ecosystem. Parasites pillage nutrients from other organisms, and mutualists coexist with their host in a mutually beneficial relationship. Harmful fungi causes some mild infections in humans such as ringworm and athlete's foot, but also some serious diseases such as trichothecene mycotoxins derived from a common grain mold.
Roughly 100 species of fungi causes disease in humans. Superficial mycoses are fungal infections through the skin, hair, or nails. Ringworm or tinea is an example of superficial mycoses. Subcutaneous mycoses are infections that enter through the skin or dermis, usually through a wound. These infections are relatively rare and confined to tropical regions. One example of subcutaneous mycoses is Sporotrichosis caused by Sporothrix schenckii. Systemic mycoses are infections that enter through the lungs, gastrointestinal tract, or the blood stream. They can be primary or opportunistic fungi infections. An example is the inhalation of Histoplasma capsulatum that causes histoplasmosis. Opportunistic fungal infections such as aspergillosis, candidosis, and cryptococcosis attack a weakened immune system. When inhaled, some fungal spores produce allergies, and when ingested, some fungi produce hallucinogenic responses. Certain species of mold produces secondary metabolites or mycotoxins that are toxic to humans. One example is the fungus Claviceps purpurea that can be found on infected rye. The fungus causes Ergotism when ingested, a disease that induces burning pains (also known as St. Anthony's Fire) and often madness. Fungal diseases may respond to various antimicrobial.
In addition to infection, fungi such as mushrooms, truffles, and morels provide nourishment. 90% of vascular plants cannot grow without a type of fungi called mycorrhizae on their roots supplying them with nutrients. Antibiotics such as penicillin and cephalosporin, and medicines such as cyclosporine are also fungi. Yeast, another fungus, is a unicellular oval or spherical organism that reproduces through budding, not binary fission. Yeast is responsible for the fermentation process and for rising of dough to make bread.
History of Fungi
According to fossil records, the first fungi appeared in the Late Proterozoic period dating between 900 and 570 million years ago. Fungi developed to thrive in both terrestrial, fresh water, and marine environments. By the Pennsylvanian Epoch 320 to 286 million years ago, all modern classes of fungi were established on earth.
The first comprehensive description of fungi was written by Italian botanist Pier Antonio Micheli in 1729. At first, botanists and taxonomists placed fungi in the Plant Kingdom, but due to the unique characteristics of fungi, a new kingdom- the Kingdom Fungi- was established in the late 1960s. Some organisms once classified as fungi (slime molds, downy mildews, and water molds) were moved to the Kingdom Protista. Some scientists suggested the creation of another kingdom, the Kingdom Stramenopila, for these organisms.
Fungi as Biological Weapons Agents
Spores of mycotoxin-producing fungi are possible anti-personnel biological weapons agents due to their stability, ease of manufacture, and ease of dissemination in aerosol form. Several species of fungi are also effective weapons against domesticated animals: rinderpest against cattle, Newcastle Diseases and aspergillosis (brooder pneumonia) against poultry, and Foot and Mouth against a variety of farm animals. Fungi such as rice blast, stem rust, sugar beet curly top virus, and tobacco mosaic virus can also serve as anti-crops agents. Genetically modified anti-crops fungi could also serve as an environmentally friendly way for authorities to eradicate illegal crops such as marijuana, poppy, and coca plants.
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