Fig. 1

Ngζ_1 expression in E. coli cells causes a lytic phenotype compensated by ngε_1 co-expression. a Growth curves of E. coli C41(DE3) cells expressing ngζ_1 (red solid line and left Y-axis) or ngζ_1(K115A) (forest-green solid line and left Y-axis) together with the corresponding propidium iodide influx into the cells (dashed lines similarly colored and right Y-axis). Control experiments in which expression of ngζ_1 or ngζ_1(K115A) was not induced are shown in light pink and lime-green. Note that growth curves of the two uninduced cell cultures as well as the PI measurements of the mutated variant (induced and not induced) fully overlay with each other. b Growth curves of E. coli BL21(DE3)-RIL cells co-expressing ngζ_1 and ngε_1. Expression of ngε_1 was induced 0 (forest-green), 15 (lime-green) and 30 min (pale-green) subsequent to ngζ_1 induction. The control experiment in which expression of ngε_1 was not induced is shown in red. c Phase contrast and fluorescence microscopy (live-dead stain) of E. coli C41(DE3) cells before and after ngζ_1 induction (30 min) and the control experiment using the inactive ngζ_1(K115A) mutant. Cells with green fluorescence have intact cell membranes and are alive. Membrane permeable cells have red fluorescence due to propidium iodide influx. Resolved bulges due to cell wall extrusions in phase-contrast microscopy images are highlighted with red arrows