As far as is described in the literature, E. coli pks+ have not yet been observed in the gut stem niche, but were shown to form biofilms together with the anaerobe B. fragilis on the colonic epithelium of colorectal cancer patients.50 It is well known that tumor tissue is hypoxic compared to healthy tissue,29 and thus could present another favorable environment for colibactin production. The gene discussed is ARAF; the disease is colorectal cancer.