(C) Cation toxicity assays and their relationship to YqgP activity. Wild type B. subtilis (BTM2, Table EV2), its variant lacking YqgP (ΔyqgP, BTM78, Table EV2), and the rescue strain ectopically expressing YqgP (BTM501, Table EV2) were cultivated in minimal M9 medium containing 10 μM MgSO4 and 1 μM each of MnCl2, ZnCl2, CoCl2, NiCl2 and CaCl2 (i.e. reference conditions), and in mid-exponential phase were stressed by the addition of either 70 µM MnCl2, 500 µM ZnCl2, 25 µM CoSO4 or 400 µM NiCl2 (pale blue area). YqgP activity specifically improved cell fitness during manganese and zinc stress, while it had no effect on growth of cells cultivated in the presence of high cobalt and nickel concentrations. Representative experiments of 2-3 independent replicates are shown. 