Fig. 3.

MgtC-dependent inhibition of Pi transport and assimilation into ATP during cytoplasmic Mg²⁺ starvation. (A) Total intracellular Pi in wild-type (14028s), mgtC (EL4), atpB (MP24), or mgtC atpB (MP25) Salmonella following 5 h of growth in MOPS medium containing 10 μM MgCl₂ and 2 mM K₂HPO₄. (B) Relative radioactive orthophosphate (³²Pi) uptake in wild-type (14028s) or mgtC (EL4) cells. Bacteria were grown in MOPS medium containing 10 μM MgCl₂ and 500 μM K₂HPO₄ during 3 h before the addition of ³²Pi to the cultures. Levels of ³²Pi accumulated in cells were determined after 30 min of labeling by liquid scintillation counting, as described in Materials and Methods. ³²Pi uptake values were normalized against the wild-type strain. (C) Intracellular ATP levels in wild-type (14028s) or mgtC (EL4) Salmonella following 5 h of growth in MOPS medium containing 10 μM MgCl₂ and the indicated concentration of K₂HPO₄ (μM Pi). Means ± SDs of at least three independent experiments are shown. **P < 0.01, ****P < 0.0001; ns, no significant difference. (A–C) Two-tailed t tests.