Fig. 4

pReX based optimization of the production of secreted SfGFP. BL21(DE3) cells harbouring pReXdsbA*sfgfp and Lemo21(DE3) cells harboring pETdsbA*sfgfp were cultured in LB medium at 30 °C. The expression of the gene encoding secretory SfGFP was induced with 400 μM IPTG for 4 h. l-rhamnose was present as indicated. a Left panel: the effect of the production of secreted SfGFP following varying gene expression levels on protein yields was monitored as fluorescence per ml of culture. The production of SfGFP under Lemo21(DE3) and pReX-based optimal conditions corresponds to 17.1 mg and 18.3 of protein produced per liter of culture [25]. Right panel The effect of the production of secretory SfGFP following varying gene expression levels on biomass formation was monitored by measuring the A₆₀₀. b Accumulation levels of IbpB in cells producing secretory SfGFP at varying l-rhamnose concentrations were monitored by immuno-blotting using an antibody against IbpB. c The localization of secretory SfGFP in BL21(DE3)/pReX and Lemo21(DE3)/pET cells cultured in the presence of the optimal concentration of l-rhamnose was monitored directly in whole cells using fluorescence microscopy. As a control Lemo21(DE3)/pETsfgfp cells producing cytoplasmic SfGFP (i.e., SfGFP not equipped with a signal sequence) were included (a version of the pictures in colour can be found in Additional file 1: Figure S2)