Fig. 3

Permeability of E. coli cell membranes after induction at different temperatures and for different lengths of time. a Outer membrane permeability was assessed using NPN fluorescence after expression had been induced at 25 °C for 60 h (♦) and 72 h (■), or at 25–30 °C (shifting from 25 °C to 30 °C at 32 h) for 60 h (◊) and 72 h (□), respectively. b Inner membrane permeability was assessed using ONPG absorbance after expression had been induced at 25 °C for 60 h (♦) and 72 h (■), or at 25–30 °C (shifting from 25 to 30 °C at 32 h) for 60 h (◊) and 72 h (□), respectively. Increases in NPN fluorescence and ONPG absorbance reflect increases in membrane permeability