Engineering a Gut Biosensor for the Detection of Colitis Using the Probiotic Yeast Strain Saccharomyces Boulardii

Inflammatory bowel disease presents a diagnostic challenge in that periodically monitoring inflammation within the intestine is difficult without invasive methods. A more convenient method to detect intestinal inflammation would be helpful to confirm clinical diagnoses and to evaluate the efficacy of therapeutic approaches. There is increased interest in using probiotics for in situ detection of intestinal diseases since they are able to survive passage through the intestine providing an opportunity to design genetically encoded biosensors to detect disesase biomarkers. Here we describe progress towards an intestinal inflammation biosensor in the probiotic yeast, Saccharomyces boulardii. We recently engineered an oxidative stress sensing biosensor within S. boulardii that has a very strong and sensitive response towards reactive oxygen species- a common marker of inflammation. Based on this sensor, we are developing a probiotic yeast reporter that could be ingested by a patient, recovered in a stool sample, plated, and visually inspected to see if it had encountered inflammation. To this end, we modified a Cre/lox system to switch the characteristic colony colour of S. boulardii from white to red upon detection of reactive oxygen species through the excision of a genomically integrated lox-flanked ADE2 cassette; the final output is then the fraction of plated red and white colonies. Here, we present results on the optimization and tuning of the oxidative stress sensor, along with preliminary results from a DSS mouse model of colitis. We believe that the results of our work could prove useful for the development of other probiotic yeast-based biosensors.