**History and Classification**:
– The term ‘yeast’ originates from Old English and has been traced back to Egyptian ruins.
– Anton van Leeuwenhoek first observed yeast microscopically in 1680.
– Louis Pasteur demonstrated the role of living yeasts in alcoholic fermentation in 1857.
– Yeasts are eukaryotic, single-celled microorganisms classified under the fungus kingdom.
– There are over 1,500 recognized yeast species, constituting 1% of described fungal species.
– Yeasts reproduce asexually through processes like budding.
– Saccharomyces cerevisiae is a well-studied yeast species used in baking, brewing, and research.
**Nutrition, Growth, and Reproduction**:
– Yeasts are chemoorganotrophs, using organic compounds as an energy source.
– They can metabolize various sugars, alcohols, and organic acids.
– Yeasts can be obligate aerobes, facultative anaerobes, or anaerobic with aerobic energy production.
– Most yeasts grow best in neutral or slightly acidic pH environments.
– Yeasts have varying temperature ranges for optimal growth.
– Yeasts reproduce through budding, conjugation, and spore formation.
– Asexual reproduction by budding is common, while some yeasts reproduce by fission.
**Ecology and Industrial Applications**:
– Yeasts are commonly found in sugar-rich environments, fruits, and plant exudates.
– They play a role in natural fermentation processes and are important components of microbial ecosystems.
– Some yeasts are used in the production of fermented foods, beverages, and biotechnological applications.
– Yeasts like Saccharomyces cerevisiae are used in baking, brewing, and various industrial processes.
– Candida albicans is an opportunistic pathogen causing infections in humans.
– Yeasts are utilized in microbial fuel cells, biofuel production, and electricity generation.
**Ecological Role and Marine Yeasts**:
– Yeasts are found in association with soil, insects, skin flora, gut flora, and deep-sea environments.
– They dominate fungal succession during fruit decay and colonize nectaries of flowers and honey stomachs of bees.
– Marine yeasts are isolated from marine environments and can produce bioactive substances.
– Some marine yeasts originate from terrestrial habitats and are used in bioethanol production with seawater-based media.
**Uses in Biotechnology and Alcoholic Beverages**:
– Yeasts are used in biotechnology for fermentation of sugars and in the production of bread, beer, wine, and xylitol.
– They are essential in making alcoholic beverages like mead, wine, beer, and distilled spirits.
– Alcoholic beverages contain ethanol produced by yeast fermentation.
– Distilled spirits like whiskey and rum are prepared by distilling ethanol solutions.
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitute 1% of all described fungal species.
| Yeast | |
|---|---|
| |
| Saccharomyces cerevisiae, a species of yeast | |
.svg)
| |
| Cross-sectional labelled diagram of a typical yeast cell | |
Scientific classification
| |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Phyla and subphyla with yeast species | |
Basidiomycota p. p. | |
Some yeast species have the ability to develop multicellular characteristics by forming strings of connected budding cells known as pseudohyphae or false hyphae, or quickly evolve into a multicellular cluster with specialised cell organelles function. Yeast sizes vary greatly, depending on species and environment, typically measuring 3–4 µm in diameter, although some yeasts can grow to 40 µm in size. Most yeasts reproduce asexually by mitosis, and many do so by the asymmetric division process known as budding. With their single-celled growth habit, yeasts can be contrasted with molds, which grow hyphae. Fungal species that can take both forms (depending on temperature or other conditions) are called dimorphic fungi.
The yeast species Saccharomyces cerevisiae converts carbohydrates to carbon dioxide and alcohols through the process of fermentation. The products of this reaction have been used in baking and the production of alcoholic beverages for thousands of years. S. cerevisiae is also an important model organism in modern cell biology research, and is one of the most thoroughly studied eukaryotic microorganisms. Researchers have cultured it in order to understand the biology of the eukaryotic cell and ultimately human biology in great detail. Other species of yeasts, such as Candida albicans, are opportunistic pathogens and can cause infections in humans. Yeasts have recently been used to generate electricity in microbial fuel cells and to 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 Ascomycota and the Basidiomycota. The budding yeasts or "true yeasts" are classified in the order Saccharomycetales, within the phylum Ascomycota.