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19. Functions of yeast ― Potential of new industrial yeast

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If yeast does not exist on earth, then there will be no tasty bread or good beer in the world. Besides bread and alcoholic drinks, yeast is also used to make wine, soy sauce, miso etc. Yeast is a single-celled microorganism and contributes to the production of seasonings and fermented foods that directly affect our diet. Yeast is also used as nutrient source when culturing other microorganisms and cells, it is also used in a wide range of fields such as yeast extract and enzymes that decompose alcohol. Yeast belongs to the fungus kingdom, and about 2,000 species have been identified so far.

The yeast (Saccharomyces spp.) used for making bread and alcoholic beverages belongs to the spore-forming group called Ascomycota. The genus Saccharomyces includes not only the so-called “conventional yeast” but also yeasts which have been used as model organisms for research. In mid-1930s, the Carlsberg Institute in Belgium succeeded in producing spores by culturing yeast under oligotrophic conditions. Later, at the University of Washington in the United States, it was discovered that the spores of some Saccharomyces yeasts can propagate vegetatively, and produce spores without mating. Due to this property, analysis of trait segregation has become possible with spores, and has greatly contributed to the development of genetics and molecular biology.

On the other hand, about 100 yeast species with functions and properties different from those of Saccharomyces yeast have been reported to date. Some of these yeasts are heat-resistant and can be cultured and fermented at temperatures above 40°C. Yeasts with thick and robust cell walls and yeasts which can grow and ferment under strong acidic conditions have also been isolated. These yeast species are called as non-conventional yeast, and are expected to have high industrial potential for oil and fat production, surfactant production, biodegradable plastic decomposition etc.

At JIRCAS, we are using yeast species which have not been put to practical use yet, such as Pichia kudriavzebii and Kluyveromyces marxianus, as experimental materials to investigate their functionality and potential as “new industrial yeasts”. Focusing on the cell wall components of new industrial yeast promote immune activation of animal cells, we are investigating the effect of yeast cell wall in activation of the immune response in animals. An example of practical application, we are developing of livestock feed that suppresses mastitis in dairy cows by utilizing the immune activation effect of yeast. Until now, antibiotics have been used to eliminate mastitis in dairy cows, but the spread of resistant bacteria due to heavy use of antibiotics poses a threat. We are conducting experiments and data analysis using new industrial yeast and candidate feed materials, aiming to develop nutritional supplements that can be used to reduce dependence on antibiotics in the future.

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Contributor: MURATA Yoshinori (Biological Resources and Post-harvest Division)

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