FIG 4.

Alkaline phosphatase reporter assays of riboswitch-adjacent gene promoters. C. difficile 630Δerm bearing promoter-phoZ reporter fusions and either vector or pDccA was grown to mid-exponential phase with the indicated concentration of nisin (µg/ml). (A) Reporter activity for C. difficile with the Cdi-1-1 (CD630_19900) promoter fusion, grown with a range of nisin concentrations. (B) Reporter activity for C. difficile with fusions to the promoter regions upstream of the indicated riboswitches (but lacking the riboswitches themselves), grown with or without 1 µg/ml nisin (black bars and white bars, respectively). The means and standard deviations of 3 biological replicates are shown. **, P < 0.01; ***, P < 0.001; and ****, P < 0.0001, using one-way ANOVA and Dunnett’s posttest, compared to the induced vector control for the respective reporter fusion.