FIG. 5.

Promoter activity in LB broth as measured by a β-galactosidase assay. L. monocytogenes DP-L2986 (dark bars), DP-L2989 (hatched bars), and DP-L2812 (see below) carrying the hly, actA, and control reverse-orientation actA promoter fusions, respectively, were cultured in buffered LB broth, and β-galactosidase activity was measured at the indicated time points. Results are expressed as units of β-galactosidase activity per 10⁷ CFU per minute. DP-L2812 background activity, which in no case exceeded 0.08 U, was subtracted from each value. The circles indicate OD₆₀₀ values for DP-L2986 and DP-L2989, which were identical over 8 h of growth. The data represent the mean ± standard deviation for three individual experiments.