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article imageMystery of unique probiotic yeast solved with CRISPR

By Tim Sandle     Sep 3, 2019 in Science
Microbiologists have found discovered that the yeast Saccharomyces boulardii produces high amounts of acetic acid. By locating the genetic basis for this, the researchers could cancel the acetic acid production to find its probiotic effect.
Saccharomyces boulardii has some special properties. The yeast was discovered In 1923 by Henri Boulard from lychees mangosteen fruit in South East Asia. This yeast has some useful probiotic properties and it has subsequently been commercialized for treatment of diarrhea and other intestinal diseases (the gastrointestinal take-over by "bad" bacteria). The commercial names for the yeast include Enterol, Floratil, Sanifort, Génolevure, Ultralevure, Bioflor, and Florastor.
Whole-genome DNA sequence analysis reveal that S. boulardii is related to the yeast S. cerevisiae, which is used in used in baking, beer brewing, wine making, bioethanol production, among other uses (so close that S. boulardii is now considered to be a subspecies of S. cerevisiae). Despite the genetic closeness, S. boulardii can be used as probiotic for gastrointestinal conditions whereas S. cerevisiae cannot. Why this is so remained a mystery, until now.
Scientists led by Professor Johan Thevelein (Leuven Center for Microbiology) have discovered has now discovered that S. boulardii can exert antibacterial activity due to its production of very high levels of acetic acid, and this acid (the basis of vinegar) strongly inhibits the growth of most bacteria.
Commenting on how this was discovered, Professor Thevelein explains in commentary sent to Digital Journal: "We were able to identify in more than eight years of tenacious research the genetic basis of this trait. We found two unique mutations in S. boulardii, that are responsible for the production of acetic acid. These mutations can act as a genetic ‘fingerprint’ that allows us to distinguish between these two types of yeast.”
The study reveals for the first time a genetic difference between S. boulardii and S. cerevisiae and it provides a scientific explanation for the superior probiotic potency of the former.
With the new finding, the scientists were able to implement CRISPR/Cas genome editing to abolish acetic acid production completely as well as switch high into very high acetic acid producers and vice versa. These modified yeast strains can now be used for the examination of acetic acid production for the probiotic power of S. boulardii in laboratory animals and to establish a reliable scientific basis for the probiotic potency of S. boulardii.
READ MORE: Revolutionizing the CRISPR method
This could lead towards improved treatments for intestinal diseases. The study has been published in the journal Genome Research, titled "Unique genetic basis of the distinct antibiotic potency of high acetic acid production in the probiotic yeast Saccharomyces cerevisiae var. boulardii."
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