Abstract
Selenium-enriched yeast (selenium yeast) are one of the most popular sources of selenium supplementation used in the agriculture and human nutritional supplements industries. To enhance the production efficiency of selenium yeast, we sought to develop a method to identify, and ultimately select for, strains of yeast with enhanced selenium accumulation capabilities. Selenite resistance of four genetically diverse strains of Saccharomyces cerevisiae was assayed in various conditions, including varying carbon sources, nitrogen sources, and phosphate amounts, and they were correlated with selenium accumulation in a commercially relevant selenium-containing growth medium. Glycerol- and selenite-containing media was used to select for six yeast isolates with enhanced selenite resistance. One isolate was found to accumulate 10-fold greater selenium (0.13 to 1.4 mg Se g−1 yeast) than its parental strain. Glycerol- and selenium-containing medium can be used to select for strains of yeast with enhanced selenium accumulation capability. The methods identified can lead to isolation of industrial yeast strains with enhanced selenium accumulation capabilities that can result in greater cost efficiency of selenium yeast production. Additionally, the selection method does not involve the construction of transgenic yeast, and thus produces yeasts suitable for use in human food and nutrient supplements.
Highlights
Selenium is an essential element for humans and animals
The amount obtained naturally is often insufficient for the optimal growth and development of animals; to meet optimal levels in animals, organic selenium supplements are often added to animal feed [2]
To create selenium-enriched yeast, cells are grown in liquid medium with a species of inorganic selenium present, which is taken up and converted to an organic species that is more assimilated by animals
Summary
Selenium is an essential element for humans and animals. It is naturally found in its inorganic form in the crust of the earth, dispersed throughout the world, though it is more concentrated in some regions than others [1]. Researchers have achieved >98% replacement of methionine by selenomethionine, and up to 3 mg total selenium per g dry weight [4,8,9] This is significantly greater than the amounts of selenium in commercial yeast. One reason for the disparity between selenium content in commercial and laboratory strains of yeast is due to a precise, and costly, manipulation of laboratory growth medium into which the selenite and yeast are inoculated. These changes to medium are likely to be too costly to reproduce on a commercial scale
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