Relative cross-membrane potential of the wild type, SCVs, and growth-compensated mutants. All values are relative to the cross-membrane potential of the wild type (white). Relative cross-membrane potentials of menadione-auxotrophic SCVs (AH875, AH847, and AH635) and hemin-auxotrophic SCV (AH868) are shown in black. Isogenic evolved mutants that additionally carry transcriptional SCV suppressor mutations affecting srrB (AH1131) and srrA (1028) are shown in gray, and translational SCV suppressor mutations affecting tRNA genes (AH1011, AH939, AH915, and AH1080), RF2 (AH1368), or S5 (AH1357) are hatched. Unless otherwise indicated, all significance values (t test) are compared to the wild-type cross-membrane potential. ns, nonsignificant; *, P < 0.05; **, P < 0.01; ***, P < 0.001.