FIG. 5.

XylE activity of H. pylori vacA::xylE transcriptional reporter strains. Specific XylE activities (milliunits per OD₆₀₀) were determined by using bacteria that had been grown in brucella broth–5% FBS for 18 h (late-log phase to early stationary phase). In all assays, the densities of bacterial suspensions were standardized by OD₆₀₀. XylE activity was quantified as described in Materials and Methods. Results represent the mean ± the standard deviation of three assays from a representative experiment. Absolute values varied slightly from trial to trial, but the overall pattern shown here is representative of three independent experiments. Results from H. pylori 86-313 (parental strain, no xylE fusion) are consistent with background levels of 2-hydroxymuconic semialdehyde production. Levels of XylE activity were significantly higher in strain 60190 VX-1 (lane 1) than in strain 86-313 VX-1 (lane 4), P < 0.001. Placement of the 86-313 vacA promoter upstream from vacA in strain 60190 VX-1 resulted in a significant decrease in XylE activity (compare lanes 2 and 3; P < 0.001) but did not reduce activity to the same level as in strain 86-313 VX-1 (lanes 4 and 5).