FIG. 4.

Complementation of ΔrpoS mutant KPR101 with intact V. vulnificus rpoS. (A) Complementation of KPR101 with the rpoS gene (in the broad-host-range pLAFR5 vector containing the V. vulnificus rpoS gene or pKP14) resulted in synthesis of σ^S, as determined by Western blotting (inset). Exponential-phase KPR101 containing pKP14 or pLAFR5 was grown in ASW supplemented with tetracycline and exposed to 880 μM H₂O₂. At several times during exposure, aliquots of the culture were removed, and the numbers of CFU per milliliter were estimated as described in Materials and Methods. The resultant values were expressed as percentages of the initial cell density, which was approximately 10⁶ CFU/ml. (B and C) The HPI activity in a crude extract from an exponential-phase KPR101 culture containing pKP14 was compared to the HPI activity of KPR101 containing pLAFR5 by either the catalase staining method with a nondenaturing gel (B) or the H₂O₂ degradation assay with a spectrophotometer (C).