Fig. 1

Enhanced and constitutive expression of OmpF in ER0808. a SDS-PAGE profile of whole bacterial lysate shows an abundant expression of OmpF. Samples (10 μL), with an approximately equal amount of cell lysate, were loaded in each lane. M marker. b Top: SDS-PAGE profile shows 3 sets of protein bands excised from Coomassie blue-stained SDS-PAGE gels (black arrows) for further analysis. Samples (10 μL) with an approximately equal amount of cell lysate, were loaded in each lane, and a rough estimate for the amount of protein in each band was ~ 10 µg. Lower: matrix-assisted laser desorption/ionization (MALDI)-time-of-flight/time-of-flight mass spectrometry of the suspected OmpF protein band from ER0808. The observed trypsin-cleaved peptides that match theoretical ones of OmpF are denoted as black bars distributed in an OmpF schematic map according to their amino acid locations, which account for a sequence coverage of 26%. c OmpF expression profiles in the ER0808 stain and its original ER2566 strain under a variety of osmolality presets for bacteria growth