Geller et al. found that Gamaproteobacteria expressing a long form of cytidine deaminase (CDD) can convert the active form of gemcitabine (2′2′-difluorodeoxycytidine) into its inactive form (2′2′-difluorodeoxyuridine) in colon cancer models [71]. This evidence concerns the gene CDA and malignant colon neoplasm.