Engineering Saccharomyces boulardii for cell surface display of heterologous protein

Saccharomyces boulardii and Saccharomyces cerevisiae share over 99 % genetic similarity yet exhibit distinct metabolic traits. While the cell surface display system of S. cerevisiae is well-documented, the equivalent system in S. boulardii has yet to be fully characterized. This study investigates the cell surface display system of S. boulardii for the expression of a heterologous protein using different anchor proteins. Six strains expressing the enhanced green fluorescent protein (Egfp) and an anchor protein as a fusion protein were constructed to visualize the cell surface display system. Then a heterologous endo-inulinase protein was expressed with selected anchor proteins through fluorescence intensity comparison. Analysis by fluorescence microscopy revealed that the anchor protein Sed1 exhibited the highest fluorescence intensity. Furthermore, expressed selected anchor proteins and heterologous protein, endo-inulinase, the engineered strain could degrade and consume almost inulin in 72 h. Through endo-inulinase expression, we confirmed that not only Egfp but also heterologous protein is well expressed, and we successfully built an S. boulardii cell surface display system.