Fig. 2

Optimization of nisin-controlled mazF gene expression in E. mundtii ST4SA. a Growth comparison of E. mundtii ST4SA transformed with the empty pNZ8048 vector (control) and E. mundtii ST4SA transformed with the PnisA-controlled mazF gene pNZmazFnisRK plasmid in sub-inhibitory concentrations of nisin (0–600 ng/ml). Significant differences were assessed using the Kruskal–Wallis nonparametric test, and are indicated with a filled circle (P < 0.05) for comparison between Control no nisin and control 400 ng/ml, an asterisk (P < 0.05) for comparison between mazFRK no nisin and mazFRK 300 ng/ml and an empty circle (P < 0.05) for comparison between mazFRK no nisin and mazFRK 400 ng/ml. b MRS agar plates representative of the effect of MazF protein expression in E. mundtii ST4SA harboring the pNZmazFnisRK plasmid in the absence of nisin (−nisin) and in the presence of nisin (+300 ng/ml nisin)