Saccharomyces boulardii

Saccharomyces boulardii is a yeast first isolated in 1923 from lychee (Litchi chinensis) and mangosteen (Garcinia mangostana) fruit peels by the French scientist Henri Boulard. Early reports described S. boulardii as a distinct species with unique taxonomic, metabolic, and genetic characteristics; however, subsequent genomic analyses have shown that it is not a separate species but a lineage of Saccharomyces cerevisiae, sharing greater than 99% genomic sequence identity with other S. cerevisiae strains. As a result, it is often referred to as S. cerevisiae var. boulardii.

S. boulardii is used as a probiotic yeast, intended to transiently colonize the gastrointestinal tract and reduce the risk of certain gastrointestinal disorders. It is able to grow at human body temperature (37°C; 98.6°F). In healthy individuals, S. boulardii is generally regarded as nonpathogenic and nonsystemic, remaining confined to the gastrointestinal tract.

Henri Boulard reportedly became interested in the yeast after observing residents of Southeast Asia consuming lychee and mangosteen skins during cholera outbreaks, a practice believed to alleviate diarrheal symptoms.

S. boulardii has also been used as a model organism in molecular biology, and the CRISPR–Cas9 genome-editing system has been demonstrated to function effectively in this yeast.