Figure 4. Stress resistance of the katA promoter mutants.

(A,B) Stress resistance in planktonic culture. Susceptibility to H₂O₂ and acidified NaNO₂ (aNO₂) were assessed for the wild type (WT) and the katA null and promoter mutant (katA, p1m, p2m, and p1p2m) cells that had been cultured for 3 h or for 6 h in LB broth (pH 6.5), and treated for 24 h with either 15 mM H₂O₂ and 200 μM NaNO₂ or in LB broth (pH 6.5) (−). Ten-fold serial cell dilutions from the 3-h (A; logarithmic) and 6-h (B; stationary) cultures were spotted on LB agar plate. The numbers indicate the log (cfu) of the applied bacterial spots. (C) Stress resistance in static culture. The wild type (WT) and the katA null and promoter mutant (katA, p1m, p2m, and p1p2m) cells were statically and anaerobically cultured for 7 days in LB broth (pH 6.5) treated for 1 h with either 100 mM H₂O₂ and 1.2 M NaNO₂ or in LB broth (pH 6.5) (−). Ten-fold serial cell dilutions from the cultures were spotted on LB agar plate. The numbers indicate the log(cfu) of the applied bacterial spots.