Design and Optimization of a Two-Component TorRST-Based Biosensor for Detection and Degradation of Trimethylamine N-Oxide

In mammals, Trimethylamine N-oxide (TMAO) is involved in various physiological processes, and is considered a biomarker for multiple diseases. As a natural molecule found in marine organisms, TMAO is also an important indicator of seafood freshness. In this study, a TMAO biosensor was developed in <i>Escherichia coli</i> harnessing TorRST two-component system. By using a cascade amplification circuit based on HrpRS-P<i>_hrpL</i>, the biosensor's dynamic range was increased from 4.1- to 10.3-fold. By optimizing the affinity between the regulatory protein TorR and DNA binding sites in promoters, the concentration for 50% of maximal effect (EC₅₀) value was reduced from 1008 to 141 μM. The biosensor was successfully used for aquatic sample detection. By introducing an exogenous TMAO degradation pathway into <i>E. coli</i> Nissle 1917, a probiotic chassis capable of TMAO detection, transportation, and degradation was constructed, providing an effective tool for rapid detection of TMAO and prevention of multiple diseases.