Table 3. Summary of system specifications of E. coli expression systems during microfluidic cultivation.

Inducer (System)	Responsiveness	Strength	Tightness	Working concentration	Growth impairment	Population
IPTG (lacY+)	+++	+++	++*	low	very high	heterogeneous
IPTG (lacY-)	++	++	+++*	low	very low	homogeneous
Galactose (galP+)	-	-	++	high	moderate	n.d.***
Arabinose (araEFGH+)	++	++	++*	high	high	partly homogeneous
m-toluic acid	+	++	-**	moderate	very low	homogeneous
Salicylic acid	+++	+++	-**	high	high	heterogeneous

* If leakiness has to be reduced further, glucose supplementation can be applied [25].

** The wildtype P_M Promoter (instead of the P_M117) can be applied for reduced basal expression [6].

*** Due to poor inducibility during microfluidic cultivation exact evaluation is impeded.