Ascomycota

The Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya, whose members are commonly known as the Sac Fungi. They are the largest phylum of Fungi, with over 30,000 species. Characteristically, when reproducing sexually, they produce nonmotile spores in a distinctive type of microscopic cell called an "ascus", meaning "sac" or "wineskin"). These spores are called ascospores. However, some members of the Ascomycota do not reproduce sexually and do not form asci or ascospores. These members are assigned to Ascomycota based upon morphological and/or physiological similarities to ascus-bearing taxa, and in particular by phylogenetic comparisons of DNA sequences.This monophyletic grouping is an extremely significant and successful group of organisms. Familiar examples of sac fungi include morels, truffles, brewer's yeast and baker's yeast, Dead Man's Fingers, cup fungi, and the majority of lichens (loosely termed "ascolichens") such as Cladonia. Many plant-pathogenic fungi belong to the Ascomycota. Commonly seen examples include apple scab, ergot, black knot, and the powdery mildews. Species of ascomycetes are also popular in the laboratory. Sordaria fimicola, Neurospora crassa and several species of yeasts are used in many genetics and cell biology experiments. Penicillium species on cheeses and in the antibiotic industry are examples of asexual taxa, otherwise known as anamorphs, that belong in the Ascomycota. Prior to definitive phylogenetic research, molds such as Penicillium were sometimes classified in an artificial phylum, called the Deuteromycota.The Ascomycota are present in all land ecosystems worldwide – they even occur in Antarctica – and their spores and hyphal fragments are distributed through the atmosphere and freshwater environments, as well as ocean beaches and tidal zones. The distribution of individual species is very variable: some are found on all continents, while for example the white truffle Tuber magnatum, which is much sought after for culinary purposes, only appears in isolated locations in Italy and France. Plant parasitic species are often restricted by their host distributions. Cyttaria is only found on Nothofagus (Southern Beech) in the Southern Hemisphere.One of their most harmful roles is as the agent of many plant diseases. For instance:    * Dutch Elm Disease, caused by the closely related species Ophiostoma ulmi and Ophiostoma novo-ulmi, has led to the death of many elms in Europe and North America.    * The originally Asian Cryphonectria parasitica is responsible for attacking Sweet Chestnuts (Castanea sativa), and virtually eliminated the once-widespread American Chestnut (Castanea dentata),    * A disease of Maize (Zea mays), which is especially prevalent in North America, is brought about by Cochliobolus heterostrophus.    * Taphrina deformans causes leaf curl of peach.    * Uncinula necator is responsible for the disease Powdery mildew, which attacks grapevines.    * Species of Monilia cause brown rot of stone fruit such as peaches (Prunus persica) and sour cherries (Prunus ceranus).    * Members of the Ascomycota such as Stachybotrys chartarum are responsible for fading of woollen textiles, which is a common problem especially in the tropics.    * Blue-green, red and brown moulds attack and spoil foodstuffs - for instance Penicillium italicum rots oranges.    * Cereals infected with Fusarium graminearum contain mycotoxins like deoxynivalenol (DON), which can lead to skin and mucous membrane lesions when eaten by pigs.    * Ergot (Claviceps purpurea) is a direct menace to humans when it attacks wheat or rye and produces highly poisonous and carcinogenic alkaloids, causing ergotism if consumed. Symptoms include hallucinations, stomach cramp, and a burning sensation in the limbs ("Saint Anthony's Fire").    * Aspergillus flavus, which grows on peanuts and other hosts, generates aflatoxin, which damages the liver and is highly carcinogenic.    * Candida albicans, a yeast which attacks the mucous membranes, can cause an infection of the mouth or vagina called thrush or candidiasis, and is also blamed for "yeast allergies".    * Fungi like Epidermophyton cause skin infections but are not very dangerous for people with healthy immune systems. However if the immune system is damaged they can be life-threatening; for instance, Pneumocystis jiroveci is responsible for severe lung infections which occur in AIDS patients.On the other hand, ascus fungi have brought some important benefits to humanity.    * The most famous case may be that of the mould Penicillium chrysogenum (formerly Penicillium notatum), which, probably to attack competing bacteria, produces an antibiotic which, under the name of Penicillin, triggered a revolution in the treatment of bacterial infectious diseases in the 20th century.    * The medical importance of Tolypocladium niveum as an immunosuppressor can hardly be exaggerated. It excretes Ciclosporin, which, as well as being given during organ transplants to prevent rejection, is also prescribed for auto-immune diseases such as multiple sclerosis, although there is some doubt over the long-term side-effects of the treatment.    * Some ascomycete fungi can be altered relatively easily through genetic engineering procedures. They can then produce useful proteins such as insulin, human growth hormone, or TPa, which is employed to dissolve blood clots.    * The red bread mold Neurospora crassa is an important model organism in biology, of which the genome has now been fully sequenced.    * Baker's Yeast (Saccharomyces cerevisiae) is used to make bread, beer and wine, during which process sugars such as glucose or sucrose are fermented to make alcohol and carbon dioxide. In the case of bread-making, the alcohol evaporates and the carbon dioxide serves to make the dough rise.    * Enzymes of Penicillium camemberti play a role in the manufacture of the cheeses Camembert and Brie, while those of Penicillium roqueforti do the same for Gorgonzola, Roquefort and Stilton.    * In Asia Aspergillus oryzae is added to a pulp of soaked soya beans to make soy sauce.    * Finally, some members of the Ascomycota are eaten with relish; morels (Morchella) and truffles (Tuber) are some of the most sought-after fungus delicacies.

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