Table 1.

Modules available for sensing intermediates in the C, N, S, and P cycles.

Analyte sensed		Name	Mechanism	Mode of prior use	Application	References
C	CO	CooA	TR	R. rubrum	N/A	Roberts et al., 2001
		RcoM	TR	E. coli	N/A	Kerby et al., 2008
	CO2	RegAB*	TCS	R. capsulatus	N/A	Ganesh et al., 2020
	CH3OH	FlhS/EnvZ	TCS	E. coli	N/A	Selvamani et al., 2017
	CH2O	FrmR	TR	E. coli	N/A	Rohlhill et al., 2017
	CH3X	Ada	TR	E. coli	N/A	Moser et al., 2013
		Unknown	Unknown	M. extorquens	Leaves	Farhan Ul Haque et al., 2013
	Vanillin	VanR	TR	E. coli	N/A	Kunjapur and Prather, 2019
		QacR	TR	Cell-free; E. coli	N/A	de los Santos et al., 2016
	Vanillic acid	VanR	TR	E. coli	N/A	Meyer et al., 2019
	p-Coumaric acid	PadR	TR	E. coli, C. glutamicum	N/A	Siedler et al., 2017
	Protocatachuate	PcaU	TR	P. putida	N/A	Jha et al., 2018
	Salicylic acid	NahR	TR	E. coli	N/A	Meyer et al., 2019
	DHBA	PcaU	TR	E. coli	N/A	Meyer et al., 2019
	Arabinose	AraC	TR	E. coli	N/A	Meyer et al., 2019
	Cellobiose	CelR	TR	E. coli	N/A	Kwon et al., 2018
	Glucose	MglB	PS	E. coli	N/A	Deuschle et al., 2005
	Maltose	MalE	PS	E. coli	N/A	Kaper et al., 2008
	Xylose	XylR	TR	E. coli	N/A	Ribeiro et al., 2013
N	${\text{NH}}_4^{+}$	Km-Amt	TCS	K. stuttgartiensis	N/A	Pflüger et al., 2018
	${\text{NO}}_3^{-}$	NarXL	TCS	E. coli	Soil	DeAngelis et al., 2005
	${\text{NO}}_2^{-}$	NarXL	TCS	E. coli	Soil	DeAngelis et al., 2005
	NO	NorR	TR	E. coli	Gut epithelium	Archer et al., 2012
		NsrR	TR	E. coli	N/A	McKay et al., 2018
	N2	NtrBC*	TCS	E. coli	N/A	Ganesh et al., 2020
		NtcA*	TR	Cyanobacteria	N/A	Ganesh et al., 2020
	Amino acids	GFP	translation	Cell-free	Serum	Jang et al., 2017
S	H2S	SQR & CstR	TR	E. coli	N/A	Liu et al., 2019
		SqrR	TR	R. capsulatus	N/A	Shimizu et al., 2017
	Polysulfide (HSnH, n ≥ 2)	CstR	TR	E. coli	N/A	Liu et al., 2019
	${\text{SO}}_4^{2-}$	SBP & AEQ	PS	Purified protein	Serum; urine	Hamorsky et al., 2012
	S4${\text{O}}_6^{2-}$	TtrSR	TCS	E. coli	Mouse gut	Daeffler et al., 2017
	S2${\text{O}}_3^{2-}$	ThsSR	TCS	E. coli	Mouse gut	Daeffler et al., 2017
P	${\text{PO}}_4^{3-}$	PstS	PS	Purified protein	N/A	Solscheid et al., 2015
	ATP	Plg2	PS	Purified protein	N/A	Branchini et al., 2015
		CRISPR/aptamer	RNA cleavage	Purified protein	N/A	Peng et al., 2020

Modules listed include both natural and engineered sensors, most of which use a single transcriptional regulator (TR), two-component system (TCS), or a protein switch (PS) to convert environmental information into biochemical information. This list excludes sensors which require electrochemical components. For each sensor, the table notes whether the mode of prior use has been within a cell, cell-free system, or isolated biomolecule. Additionally, it notes whether there has been a complex sample application in soil, serum, urine, plant leaves, or animals. Most sensors have not yet been applied (N/A) in a complex setting. Asterisks (*) denotes sensors that respond to inputs indirectly, while daggers (†) indicate that the sensing mechanism is not fully characterized.