Table 1.

Process technological methods for expression tuning

Induction method	Mode of action	Comments
One-point addition of inducer	The concentration of inducer is adjusted to a defined concentration in the beginning of the induction phase	Widely applied, however, inducer concentration can change throughout the process due to catabolism, dilution by growth, or inactivation (Marbach and Bettenbrock 2012; Novick and Weiner 1957)
Inducer titration	Non-metabolizable inducer is continuously supplied to keep the specific inducer concentration (inducer/biomass) constant	Independent control of sugar uptake rate (growth rate) and induction rate is possible (Striedner et al. 2003)
Metabolizable inducer	Metabolizable inducer is continuously supplied and metabolized by the cells	Induction rate and uptake rate of metabolizable inducer are tightly coupled
Mixed feed	Both primary growth substrate and metabolizable inducer are simultaneously supplied and metabolized by the cells	Independent control of specific growth rate and induction rate is possible (Sagmeister et al. 2013a).