(A) Detection and quantification of the cleavage of endogenous MgtE by YqgP in living B. subtilis cells (BS72, Table EV2) depending on the concentrations of magnesium and manganese ions. Cells were cultivated in glucose M9 minimal medium with limiting (0.01 mM) or high (1 mM) concentration of MgSO4, in the presence or absence of 100 μM MnCl2, and analysed by western blotting with near-infrared detection (upper panel). Black arrow denotes full-length MgtE, and red arrow denotes its N-terminal cleavage product formed by YqgP. The corresponding fluorescence signals were quantified by densitometry, and are displayed as relative specific activity, which is substrate conversion normalized to enzyme expression level (lower panel). 