Engineered spermidine-secreting Saccharomyces boulardii ameliorate colitis and colon cancer in mice

Experimental studies suggest that the probiotic yeast Saccharomyces boulardii can mitigate the symptoms of inflammatory bowel disease. However, these results are equivocal and S boulardii probiotic therapy has not gained widespread acceptance in clinical practice. To assess whether the therapeutic properties of S boulardii might be improved upon, we engineered S boulardii to overproduce and secrete spermidine, a pro-regenerative natural metabolite. We employed CRISPR gene deletion and transposon-mediated gene integration to manipulate expression of key enzymes in the polyamine synthetic and transport pathways. We tested the engineered yeast by oral gavage of mice treated with azoxymethane and dextran sulfate sodium to induce chronic colitis and colon cancer. We demonstrate that oral delivery of spermidine-secreting S boulardii in mice populates the gastrointestinal tract with viable spermidine-secreting S boulardii cells and raises free spermidine levels in the gastrointestinal tract. Strikingly, spermidine-secreting S boulardii strains were significantly more effective than wild-type S boulardii in reducing dextran sulfate sodium-induced colitis as well as colitis-associated colon cancer in mice. These results suggest that in situ spermidine secretion by engineered synthetic biotic yeast strains may be an effective and low-cost therapy to mitigate inflammatory bowel disease and colon cancer.