Design of a Transcriptional Biosensor for the Portable, On-Demand Detection of Cyanuric Acid

Rapid molecular biosensing is an emerging application
area for
synthetic biology. Here, we engineer a portable biosensor for cyanuric
acid (CYA), an analyte of interest for human and environmental health,
using a LysR-type transcription regulator (LTTR) from Pseudomonas within the context of Escherichia coli gene expression
machinery. To overcome cross-host portability challenges of LTTRs,
we rationally engineered hybrid Pseudomonas–E. coli promoters by integrating DNA elements required for transcriptional
activity and ligand-dependent regulation from both hosts, which enabled E. coli to function as a whole-cell biosensor for CYA.
To alleviate challenges of whole-cell biosensing, we adapted these
promoter designs to function within a freeze-dried E. coli cell-free system to sense CYA. This portable, on-demand system robustly
detects CYA within an hour from laboratory and real-world samples
and works with both fluorescent and colorimetric reporters. This work
elucidates general principles to facilitate the engineering of a wider
array of LTTR-based environmental sensors.