SRP436595 PRJNA970530 Effect of FOS and S. boulardii on intestinal microbiota of healthy primary and secondary school students in an in vitro fermentation model Fructo-oligosaccharides (FOS) is a typical prebiotic with both physiological characteristics of water-soluble dietary fiber and super bifidus factor, which is widely used in functional foods and healthcare products. Saccharomyces boulardii is a kind of fungal probiotic which is often used to assist in the treatment of diarrhea in clinic. At present, synbiotics composed of prebiotics and probiotics have attracted wide attentions, but the correlative study on the combination of FOS and S. boulardii is still rare. Therefore, in this study, the intervention effect of FOS, S. boulardii and their combination on intestinal microbiota of healthy primary and secondary school students was analyzed by in vitro simulated fermentation technology. These results revealed that S. boulardii alone could not effectively regulate the structure and metabolism of intestinal microbiota in the absence of carbon sources. While FOS alone and the combination of FOS/S. boulardii can effectively regulate intestinal microbiota. Both of them can significantly inhibit the growth of potential pathogens Escherichia-Shigella and Bacteroides and the excessive production of harmful gases H2S and NH3, significantly promote the growth of probiotic bacteria Bifidobacterium and Lactobacillus, significantly reduce the environmental pH, and significantly promote a variety of physiological functions related to synthesis and metabolism. The difference is that FOS can also significantly promote the growth of probioticbacteria Faecalibacterium and Blautia and the production of acetic acid, while the combination of FOS/S. boulardii can significantly inhibit the growth of Collinsella, extremely significantly promote the growth of Lactobacillus, and further improve the relative abundance of functional genes of Carbon metabolism and Pyruvate metabolism. In conclusion, the combination of FOS/S. boulardii can exert a different effect in regulating intestinal microbiota compared to using it alone. The results of this study can provide new insights for the development of both as synbiotics.