FIG. 6.

H₂O₂ disk assay. Photos showing the zones of inhibition by H₂O₂ in E. coli K-12 (wild type) (A), GS09 (oxyR::kan mutant) (B), and E. coli K-12 strain GS09 complemented with the oxyR gene (pHJToxyR-1) from N. gonorrhoeae (C). (D) Histogram showing the results of H₂O₂ disk assay in E. coli. In the assay, cells were grown on LB agar in the presence or absence of 0.5 mM isopropyl-β-d-thiogalactopyranoside (IPTG). Sensitivity to H₂O₂ was measured by the zone of inhibition (diameter). The zone of inhibition was measured in three dimensions, and the mean values and standard deviations were calculated. The y-axis error bars each indicate ±1 standard deviation of the mean. Student's t test was performed to determine the statistical significance among different samples. The E. coli K-12 oxyR::kan mutant was significantly more sensitive to H₂O₂ than the wild type and the complemented strain (P = 0.03315 and 0.01757, respectively).