Fig. 3

Optimal IPTG concentration in induction of LPP′-OmpA′-SUMO-Δ59 Sortase A-LPETG-PEN-HuscFv34-6× His expression on the bacterial surface. The transformed BL21 (DE3) ΔA competent E. coli was grown under induction of different IPTG concentrations (0.025, 0.05, 0.1, 0.5 and 1.0 mM) at 37 °C. The bacterial cells were fixed with 4% paraformaldehyde, washed, incubated with mouse mAb to HuscFv34, washed, added with goat anti-mouse Ig-Alexa Fluor 488 conjugate, washed, stained with DAPI, washed, and resuspended in 1% paraformaldehyde. The PEN-HuscFv34-6× His displayed on bacterial cells was determined by flow cytometry. Q1 and Q2, transformed E. coli cells displaying Lpp′-OmpA′-SUMO-Δ59 Sortase A-LPETG-PEN-HuscFv34-6× His fusion protein; Q3 and Q4, E. coli cells that did not display the fusion protein. Q2 and Q3, intact bacterial cells with nuclei; Q1 and Q4, bacterial cells without nuclei or dead cells