FIG. 3.

Effect of the cyoB mutation on induction of the PalkB promoter in cells growing with different carbon sources. P. putida strains PBS4 and PBS4B1 (PBS4 with a knockout mutation at the cyoB gene) were grown in duplicate flasks either in LB medium (B) or in minimal salts medium containing either citrate (Cit) (A), succinate (Scc) (C), or lactate (Lac) (D) as the carbon source. At an A₆₀₀ of 0.08, the nonmetabolizable inducer DCPK was added to one of the flasks; the other was left as a noninduced control. Aliquots were taken at different times, and the β-galactosidase activity was measured. The plots show the values observed for induced cultures (noninduced cultures had very low β-galactosidase activities [30 to 100 Miller units] and are not represented). The values shown correspond to three to six independent assays, all of which are represented on the same plot.