Novel insights in genetic transformation of the probiotic yeast Saccharomyces boulardii

Saccharomyces boulardii (S. boulardii) is a probiotic yeast related to Saccharomyces cerevisiae (S. cerevisiae) but with distinct genetic, taxonomic, and metabolic properties. S. cerevisiae has been used extensively in biotechnological applications. Currently, many strains are available, and multiple genetic tools have been developed, which allow the expression of several exogenous proteins of interest with applications in the fields of medicine, biofuels, the food industry, and scientific research, among others. Although S. boulardii has been widely studied due to its probiotic properties against several gastrointestinal tract disorders, very few studies addressed the use of this yeast as a vector for expression of foreign genes of interest with biotechnological applications. Here we show that, despite the similarity of the two yeasts, not all genetic tools used in S. cerevisiae can be applied in S. boulardii. While transformation of the latter could be obtained using a commercial kit developed for the former, consequent screening of successful transformants had to be optimized. We also show that several genes frequently used in genetic manipulation of S. cerevisiae (e.g., promoters and resistance markers) are present in S. boulardii. Sequencing revealed a high rate of homology (>96%) between the orthologs of the two yeasts. However, we also observed some of them are not eligible to be targeted for transformation of S. boulardii. This work has important applications toward the potential of this probiotic yeast as an expression system for genes of interest.