Colorectal cancer includes tumors affecting a segment of the large intestine (colon) and rectum. It is treatable and, in most cases, curable when detected early, before it hasn’t spread to other organs. However, the diagnosis requires a biopsy, made ​​by handset introduced via rectum. Noticeably, this procedure is highly invasive and often inhibits patients to submit to this practice, hampering the discovery of cancer at an early stage and thereby reducing the chances of effective treatment and cure.

On our institution, a modified probiotic strain of Saccharomyces cerevisiae was isolated from local beverage. Our objective is to introduce this strain as a new probiotic chassis on iGEM, and also to develop a gene circuit that allows it to detect one or more stool biomarkers for colorectal cancer on the intestine and report with a color change on the feces. We chose L-DNA (long DNA molecules) as biomarker, and designed a chimeric protein using TALE DNA-Binding Domains and a split version of mCherry. This protein can detect certain repetitive sequences on DNA and emit red fluorescence, which when measured serve as proxy for the DNA size. Since RFP emission falls on the visible spectrum, it can also be used for staining the feces, allowing for a patient consuming the probiotic to become aware of the possibility of the developing problem just by checking on the color of their stool.