Fig. 1

Growth, susceptibility and morphology of E. coli BL21(DE3)/pX12345 after lactose induction and subcellular location of X12345 in E. coli BL21(DE3). a Q-TOF MS of purified extracellular X12345 from BL21(DE3)/pX12345. The major peak has a molecular mass of 39,423.49 Da. b Growth curve of BL21(DE3)/pX12345 after lactose induction. The cellular density of bacterial cultures was determined at each indicated time points after induction with 2% lactose in TB medium by measuring optical densities at 600 nm. c Analysis of solubility and subcellular location of X12345 expressed in BL21(DE3). Cultures of BL21(DE3)/pX12345 at different induction time points were harvested and fractionated as described in “Materials and methods” section. Protein samples from these fractions were analyzed by 12% SDS-PAGE and western blotting with antibodies to his-tag of X12345, MBP, and GroEL. The lane loadings are directly comparable. SF soluble fraction, IF insoluble fraction, C cells, M medium, P1 periplasm fraction (hypertonic solution fraction), P2 periplasm fraction (hypotonic solution fraction), S spheroplasts. d FESEM of BL21(DE3)/pET28a and BL21(DE3)/pX12345 after lactose induction for each indicated time. e Susceptibility of induced BL21(DE3)/pX12345 or BL21(DE3)/pET28a to antibiotics and other compounds. After lactose induction for 8 (circles), 12 (triangles) or 24 h (squares), BL21(DE3)/pX12345 (solid line) or BL21(DE3)/pET28a (break line) cells were cultured aerobically at 37 °C in LB medium with different concentrations of erythromycin, rifampicin, deoxycholate or lysozyme for ~ 12 h, and cell growth was measured at OD₆₀₀. Results are mean ± SD of triplicate observations