A Nitrate/Nitrite Biosensor Designed with an Antiterminator for In Vivo Diagnosis of Colitis Based on Bacteroides thetaiotaomicron.

Bacteroides thetaiotaomicron is a common microorganism in the human gut that has been linked to health benefits. Furthermore, it is an emerging synthetic biology chassis with the potential to be modified into diagnostic or therapeutic engineered probiotics. However, the absence of biological components limits its further applications. In this study, we developed an antiterminator microbial whole-cell biosensor (MWCB) based on B. thetaiotaomicron. The antiterminator-based element allows the chassis to detect colitis in mice by responding to nitrate and nitrite in an inflammatory environment. In particular, the nitrate/nitrite-inducible promoter was obtained by combining the constitutive promoter with the inducible terminator. Subsequently, the promoter and RBS were replaced to optimize a sensitive and specific response to nitrate/nitrite. A preliminary in vitro assessment was conducted to ascertain the functionality of the biosensor. Its in vivo sensing ability was evaluated in a chemically induced mouse model of ulcerative colitis (UC). The results demonstrated that the MWCB exhibited a robust response to colitis, with a notable positive correlation between the intensity of the response and the level of inflammation. This novel sensing element may provide a new avenue for the development of components for unconventional chassis, like B. thetaiotaomicron. It will also facilitate the development of engineered probiotics based on B. thetaiotaomicron, thereby providing patients with a wider range of medical treatment options.