The ChpR transcriptional regulator of Sinorhizobium meliloti senses 3,5,6-trichloropyridinol, a degradation product of the organophosphate pesticide chlorpyrifos.

The global use of organophosphate insecticides (OPPs) and the growing concern of off-target side effects due to OPP exposure has prompted the need for sensitive and economical detection methods. Here we set out to engineer a previously identified OPP responsive transcription factor, ChpR, from to respond to alternative OPPs and generate a repertoire of whole-cell biosensors for OPPs. The ChpR transcription factor and cognate promoter P have been shown to activate transcription in the presence of the OPP chlorpyrifos (CPF). Utilizing a GFP reporter regulated by ChpR in a whole-cell biosensor we found that the system responds significantly better to 3,5,6-trichloro-2-pyridinol (TCP), the main degradation product of CPF, compared to CPF itself. This biosensor was able to respond to TCP at 390 nM within 4 h compared to 50 µM of CPF in 7 h. The ChpR-P , and the activating ligand TCP, were able to regulate expression of a kanamycin resistance/sucrose sensitivity () selection/counterselection module suitable for high throughput mutagenesis screening studies. The ability to control both GFP and the module demonstrates the utility of this reporter for the detection of CPF affected areas. The ChpR-P system serves as an additional positive regulator switch to add to the growing repertoire of controllers available within synthetic biology.