Table 2.

Transcription factors used as sensor elements in WCBs for heavy metal detection.

Transcription Factor (TF)	Type	Genes Controlled	Organisms	WCB Applications	References
MerR	Activator	merA (mercury reductase), merB (permease), merC (metallothionein)	E. coli, P. aeruginosa PAO1, P. putida	Detection of mercury in seawater and lakes using GFP, RFP, violacein, pyocyanin, Luciferase	[95,96,97,98,99,100,101,102]
ArsR/SmtB	Repressor	arsA, arsB, arsC (E. coli); arsC, arsD, arsR (B. subtilis)	P. aeruginosa PAO1, P. putida, Enterobacteria, E. coli	Detection of arsenic in lakes and groundwater using GFP and β-Galactosidase; detection of cadmium, lead, antimony	[103,104,105,106,107,108,109,110,111,112,113,114,115]
Fur	Repressor/Activator	Iron-responsive genes, siderophore synthesis genes, ROS defence, respiration, chemotaxis, nitrogen metabolism, photosynthesis, virulence, glycolysis, citric acid cycle genes	E. coli, Corynebacterium, Streptomyces, Mycobacterium	Detection of iron in freshwater and South West Pacific using bioluminescence in P. putida	[34,116,117,118,119,120,121,122,123]
DtxR	Repressor/Activator	Iron uptake and metabolism genes	Corynebacterium, Streptomyces, Mycobacterium	N.D.	[122,123]
IscR	Repressor	iscSUA-hscBA-fdx iron–sulfur cluster	E. coli	N.D.	[124,125,126,127,128]