Pichia anomala is a most interesting yeast species, from a number of environmental, industrial and medical aspects. This yeast has been isolated from very diverse natural habitats (e.g. in foods, insects, wastewaters etc.) and it also exhibits wide metabolic and physiological diversity. Some of the activities of P. anomala, particularly its antimicrobial action, make it a very attractive organism for biological control applications in the agri-food sectors of industry. Being a 'robust' organism, it additionally has potential to be exploited in bioremediation of environmental pollutants. This paper provides an overview of cell physiological characteristics (growth, metabolism, stress responses) and biotechnological potential (e.g. as a novel biocontrol agent) of P. anomala and compares such properties with other yeast species, notably Saccharomyces cerevisiae, which remains the most exploited industrial microorganism. We await further basic knowledge of P. anomala cell physiology and genetics prior to its fuller commercial exploitation, but the exciting biotechnological potential of this yeast is highlighted in this paper.
The ascomycetous yeast Pichia anomala is frequently associated with food and feed products, either as a production organism or as a spoilage yeast. It belongs to the nonSaccharomyces wine yeasts and contributes to the wine aroma by the production of volatile compounds. The ability to grow in preserved food and feed environments is due to its capacity to grow under low pH, high osmotic pressure and low oxygen tension. A new application of P. anomala is its use as a biocontrol agent, which is based on the potential to inhibit a variety of moulds in different environments. Although classified as a biosafety class-1 organism, cases of P. anomala infections have been reported in immunocompromised patients. On the other hand, P. anomala killer toxins have a potential as antimicrobial agents. The yeast can use a broad range of nitrogen and phosphor sources, which makes it a potential agent to decrease environmental pollution by organic residues from agriculture. However, present knowledge of the physiological basis of its performance is limited. Recently, the first studies have been published dealing with the global regulation of the metabolism of P. anomala under different conditions of oxygenation.
Yeast Physiology And Biotechnology Pdf Download
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There have been many numerous books in recent years dealing with yeast molecular biology and genetics, but very few of them examine the subject of yeast physiology. This book fills this vital gap in the literature by comprehensively covering salient areas of yeast growth and metabolism and their linkage to biotechnology.
Yeasts are the world's premier industrial micro-organisms. In addition to their wide exploitation in the production of foods, beverages and pharmaceuticals, yeasts also play significant roles as model eukaryotic cells in furthering our knowledge in the biological and biomedical sciences. In order for modern biotechnology to fully exploit the activities of yeasts, it is essential to appreciate aspects of yeast cell physiology. In recent years, however, our knowledge of yeast physiological phenomena has lagged behind that of yeast genetics and molecular biology. Yeast Physiology and Biotechnology redresses the balance by linking key aspects of yeast physiology with yeast biotechnology. Individual chapters provide broad and timely coverage of yeast cytology, nutrition, growth and metabolism - important aspects of yeast cell physiology which are pertinent to the practical uses of yeasts in industry. The final chapter reviews traditional, modern and emerging biotechnologies in which roles of yeasts in the production of industrial commodities and their value in biomedical research are fully discussed. Relevant aspects of classical and modern yeast genetics and molecular biology are fully integrated into the appropriate chapters. This up-to-date and fully referenced book is aimed at advanced undergraduate and postgraduate bioscience students,but will also prove to be a valuable source of information for yeast researchers and technologists.
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.[1][2][3] They are estimated to constitute 1% of all described fungal species.[4]
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.[8] 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.[9] 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[10] 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,[11] 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,[12] within the phylum Ascomycota.
The word "yeast" comes from Old English gist, gyst, and from the Indo-European root yes-, meaning "boil", "foam", or "bubble".[13] Yeast microbes are probably one of the earliest domesticated organisms. Archaeologists digging in Egyptian ruins found early grinding stones and baking chambers for yeast-raised bread, as well as drawings of 4,000-year-old bakeries and breweries.[14] Vessels studied from several archaeological sites in Israel (dating to around 5,000, 3,000 and 2,500 years ago), which were believed to have contained alcoholic beverages (beer and mead), were found to contain yeast colonies that had survived over the millennia, providing the first direct biological evidence of yeast use in early cultures.[15] In 1680, Dutch naturalist Anton van Leeuwenhoek first microscopically observed yeast, but at the time did not consider them to be living organisms, but rather globular structures[16] as researchers were doubtful whether yeasts were algae or fungi.[17] Theodor Schwann recognized them as fungi in 1837.[18][19]
By the late 18th century two yeast strains used in brewing had been identified: Saccharomyces cerevisiae (top-fermenting yeast) and S. pastorianus (bottom-fermenting yeast). S. cerevisiae has been sold commercially by the Dutch for bread-making since 1780; while, around 1800, the Germans started producing S. cerevisiae in the form of cream. In 1825, a method was developed to remove the liquid so the yeast could be prepared as solid blocks.[21] The industrial production of yeast blocks was enhanced by the introduction of the filter press in 1867. In 1872, Baron Max de Springer developed a manufacturing process to create granulated yeast, a technique that was used until the first World War.[22] In the United States, naturally occurring airborne yeasts were used almost exclusively until commercial yeast was marketed at the Centennial Exposition in 1876 in Philadelphia, where Charles L. Fleischmann exhibited the product and a process to use it, as well as serving the resultant baked bread.[23]
Yeasts are chemoorganotrophs, as 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 fructose, or disaccharides such as sucrose and maltose. Some species can metabolize pentose sugars such as ribose,[25] 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 bacteria, no known yeast species grow only anaerobically (obligate anaerobes). Most yeasts grow best in a neutral or slightly acidic pH environment.
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, Wallerstein Laboratories nutrient agar, yeast 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. The fungicide cycloheximide is sometimes added to yeast growth media to inhibit the growth of Saccharomyces yeasts and select for wild/indigenous yeast species. 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. It is usually the result of exposure to air. Although harmless, it can give pickled vegetables a bad flavor and must be removed regularly during fermentation.[27]
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 peaches), and exudates from plants (such as plant saps or cacti). Some yeasts are found in association with soil and insects.[28][29] Yeasts from the soil and from the skins of fruits and berries have been shown to dominate fungal succession during fruit decay.[30] The ecological function and biodiversity of yeasts are relatively unknown compared to those of other microorganisms.[31] Yeasts, including Candida albicans, Rhodotorula rubra, Torulopsis and Trichosporon cutaneum, have been found living in between people's toes as part of their skin flora.[32] Yeasts are also present in the gut flora of mammals and some insects[33] and even deep-sea environments host an array of yeasts.[34][35] 2351a5e196
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