Fig. 3

a Principle of the indirect stress sensor using positive and negative control to trigger IM stress. b Relative mKate2 fluorescence of an equal number (OD₆₀₀ = 0.3, mid-exponential phase) of Escherichia coli (E. coli) DE3 cells (See Additional file 1: Table S2 for more details) producing either NlpE (IMP of E. coli, positive control) or sfGFP (cytoplasmatic superfolder green fluorescent protein, negative control) for several IPTG-concentrations. The fluorescence of NlpE and sfGFP producing DE3 cells at 0 mM IPTG is arbitrarily set to one and fluorescence of other IPTG-concentrations was compared to this value. IM = inner-membrane, IMP = inner-membrane protein, mKate2 = red fluorescent protein