A. The ΔspxA1 strain is unable to grow on aged TSB unlike the wild-type parent and the ΔspxA2 mutant. Strains: 1, wt (7702 Sterne); 2, ΔspxA1 (ORB8170); 3, ΔspxA2 (ORB8438); 4, wtStrr (7702 SR1); 5, ΔspxA1Strr (ORB8398); 6, ΔspxA1Strr+spxA1DD (ORB8404).
B. The saiR mutations restore the growth of the ΔspxA1 mutant on aged TSB agar, but not of the ΔspxA1ΔspxA2 mutant. Strains: 1, wt (7702 Sterne); 2, ΔspxA1 (ORB8170); 3, ΔspxA1sup6 (ORB8492); 4, ΔspxA1ΔsaiR (ORB8606); 5, ΔspxA1ΔspxA2 (ORB8285); ΔspxA1ΔspxA2ΔsaiR (ORB8564).
C. The substitution of C96 in SaiR leads to a loss of repressor activity. Strains: 1, wt (7702 Sterne); 2, ΔspxA1 (ORB8170); 3, ΔspxA1ΔsaiR (ORB8606); 4, ΔspxA1ΔsaiR+saiR(C89S) (ORB8723); 5, ΔspxA1ΔsaiR+saiR(C96S) (ORB8724); 6, ΔspxA1ΔsaiR+saiR(wt) (ORB8725).