Table 1:

Bacteria engineered as diagnostics.

Diagnostic application	Detected compound or condition	Sensor type	Sensor genetic part	Circuit	Reporter	Strain	Ref.
Gut inflammation	Tetrathionate	TCS	Salmonella typhimurium TtrSR-PttrBCA	CI/Cro memory switch	β-galactosidase	E. coli NGF-1	[55]
Gut inflammation	Tetrathionate	TCS	Shewanella baltica TtrSR-PttrB	NA	GFP	EcN	[56]
Gut inflammation	Thiosulfate	TCS	Shewanella halifaxensis ThsSR-PphsA	NA	GFP	EcN	[56]
Gut bleeding	Heme	T-TF	E. coli O157:H7 ChuA-L. lactis HrtR-PL(HrtO)	NA	luxCDABE combined with microelectronics	EcN	[57]
Cholera	Cholera autoinducer 1 (CAI-1)	TCS	Engineered chimera†	TetR (inverter)	β-lactamase	L. lactis	[4]
Cell division	aTc	TF	TetR-Ptet	CI/Cro memory switch‡	β-galactosidase	E. coli NGF-1	[59]
Cancer	Tumors colonized by engineered EcN	NA	NA	NA	β-galactosidase converting LuGal into luciferin	EcN	[65]
Inflammation	Nitrogen oxides	TF	E. coli NsrR-PYeaR	BxbI or TP901-9 recombinases	GFP	E. coli DH5αZ1	[64]
Diabetes	Glucose	TCS	E. coli CpxAR-PcpxP	BxbI or TP901-9 recombinases	GFP	E. coli DH5αZ1	[64]

Abbreviations: AHL, N-acyl homoserine lactone; aTc, anhydrotetracycline; EcN, E. coli Nissle 1917; GFP, green fluorescent protein; TCS, two-component system, consisting of a histidine kinase and a response regulator; TF, transcription factor; T-TF, transporter-transcription factor; LuGal, a soluble conjugate of luciferin and galactose; NA, not applicable. If NA is present in the “Circuit” column, the sensor directly regulates expression of the reporter; otherwise, there is an additional circuit layer.

^†The TCS is an engineered chimera where the CAI-1-binding domain of V. cholerae CqsQ is fused to the signal transduction domain of Lactococcus lactis NisK. The chimeric histidine kinase interacts with the response regulator NisR.

^‡Switching occurs only in actively dividing engineered E. coli.