Yeasts are eukaryoticsingle-celled microorganisms classified as members the fungus kingdom. The first yeast originated hundreds of millions of years ago, and 1, species are currently identified. Yeasts, with their single-celled growth habit, can be contrasted with moldswhich grow hyphae. Fungal species that can take both forms depending on temperature or other conditions are called dimorphic fungi "dimorphic" means "having two forms".
Researchers have used it to gather information about the biology of the eukaryotic cell and ultimately human biology. Yeasts have recently been used to generate electricity in microbial fuel cells and produce ethanol for the biofuel industry. Yeasts do not form a single taxonomic or phylogenetic grouping. The term "yeast" is often taken as a synonym for Saccharomyces cerevisiae but the phylogenetic diversity of yeasts is shown by their placement in two separate phyla: The budding yeasts "true yeasts" are classified in the order Saccharomycetales within the phylum Ascomycota.
The word "yeast" comes from Old English gistgystand from the Indo-European root yes-meaning "boil", "foam", or "bubble".
Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeast-raised bread, as How do yeast reproduce sexually as drawings of 4,year-old bakeries and breweries. By the late 18th century, two yeast strains used in brewing had been identified: Saccharomyces cerevisiae top-fermenting yeast and S.
Ina method was developed to remove the liquid so the yeast could be prepared as solid blocks. InBaron Max de Springer developed a manufacturing process to create granulated yeast, a technique that was used until the first World War.
Fleischmann exhibited the product and a process to use it, as well as serving the resultant baked bread. Yeasts are chemoorganotrophsas they use organic compounds as a source of energy and do not require sunlight to grow. Carbon is obtained mostly from hexose sugars, such as glucose and fructoseor disaccharides such as sucrose and maltose. Some species can metabolize pentose sugars such as ribose,  alcohols, and organic acids.
Yeast species either require oxygen for aerobic cellular respiration obligate aerobes or are anaerobic, but also have aerobic methods of energy production facultative anaerobes. Unlike bacteriano known yeast species grow only anaerobically "How do yeast reproduce sexually" anaerobes.
Most yeasts grow best in a neutral or slightly acidic pH environment.
Yeasts vary in regard to the temperature range in which they grow best. In general, yeasts are grown in the laboratory on solid growth media or in liquid broths. Common media used for the cultivation of yeasts include potato dextrose agar or potato dextrose broth How do yeast reproduce sexually, Wallerstein Laboratories nutrient agaryeast peptone dextrose agar, and yeast mould agar or broth.
Home brewers who cultivate yeast frequently use dried malt extract and agar as a solid growth medium. This will change the yeast process. The appearance of a white, thready yeast, commonly known as kahm yeast, is often a byproduct of the lactofermentation or pickling of certain vegetables, usually the result of exposure to air.
Although harmless, it can give pickled vegetables a bad flavor and must be removed regularly during fermentation. Yeasts are very common in the environment, and are often isolated from sugar-rich materials. Examples include naturally occurring yeasts on the skins of fruits and berries such as grapes, apples, or peachesand exudates from plants such as plant saps or cacti.
Some yeasts are found in association with soil and insects. An Indian study of seven bee species and 9 plant species found 45 species from 16 genera colonise the nectaries of flowers and honey stomachs of bees. Most were members of the genus Candida ; the most common species in honey stomachs was Dekkera intermedia and in flower nectaries, Candida blankii. The yeast has a negative effect on the bacteria that normally produce "How do yeast reproduce sexually" to kill the parasite, so may affect the ants' health by allowing the parasite to spread.
Certain strains of some species of yeasts produce proteins called yeast killer toxins that allow them to eliminate competing strains. See main article on killer yeast. This can cause problems for winemaking but could potentially also be used to advantage by using killer toxin-producing strains to make the wine. Yeast killer toxins may also have medical applications in treating How do yeast reproduce sexually infections see "Pathogenic yeasts" section below.
Yeasts, like all fungi, may have asexual and sexual reproductive cycles. The most common mode of vegetative growth in yeast is asexual reproduction by budding. The nucleus of the parent cell splits into a daughter nucleus and migrates into the daughter cell.
The bud continues to grow until it separates from the parent cell, forming a new cell. Some yeasts, including Schizosaccharomyces pombereproduce by fission instead of budding,  thereby creating two identically sized daughter cells. In general, under high-stress conditions such as nutrient starvation, haploid cells will die; under the same conditions, however, diploid cells can undergo sporulation, entering sexual reproduction meiosis and producing a variety of haploid sporeswhich can go on to mate conjugatereforming the diploid.
The haploid fission yeast Schizosaccharomyces pombe is a facultative sexual microorganism that can undergo mating when nutrients are limiting. Katz Ezov et al. In nature, mating of haploid cells to form diploid cells is most often between members of the same clonal population and out-crossing is uncommon. Some pucciniomycete yeasts, in particular species of Sporidiobolus and Sporobolomycesproduce aerially dispersed, asexual ballistoconidia. The useful physiological properties of yeast have led to their use in the field of biotechnology.
Fermentation of sugars by yeast is the oldest and largest application of this technology. Many types of yeasts are used for making many foods: Yeasts include some of the most widely How do yeast reproduce sexually model organisms for genetics and cell biology. Alcoholic beverages are defined as beverages that contain ethanol C 2 H 5 OH. Beverages such as mead, wine, beer, or distilled spirits all use yeast at some stage of their production.
A distilled beverage is a beverage containing How do yeast reproduce sexually that has been purified by distillation.