Fig. 3.
Engineering L. lactis probiotic strain for the detection of cholera infection. HR4M, a functional hybrid receptor variant was constructed by fusing transmembrane ligand binding domain of CqsS from V. cholerae with the signal transduction domain of NisK from L. lactis. The V. cholerae-sensing element consists of a HR4M-NisR two-component sensing system and a TetR-Pxyltet signaling system. In the absence of CAI-1, the phosphorylated NisR activates the expression of tetR, which is a transcriptional repressor for the promoter Pxyltet, thus lead to inhibition of the reporter gene. In the presence of CAI-1, the HR4M-NisR two-component sensing system stops its phosphorelay, thus repressing the expression of tetR and resulting in the activation of the reporter gene