Figure 3.

(A) Growth curves in shaken liquid cultures shows no difference between wild-type (black) and rhlA⁻ (red), in spite of the large amounts of biosurfactants secreted by WT. Inset: The ratio of WT to rhlA⁻ CFUs in a mixed culture grown in liquid (starting ratio of 1:1) is maintained even after four daily passages to fresh medium, again showing a lack of a fitness difference. (B) A GFP fusion to the rhlAB promoter in the WT shows that rhlAB expression is delayed until stationary phase. In A and B-thick lines are the median among 6 replicates with thinner lines showing the limits of 66 percentile among replicates. The same criterion was used in all following plots of growth curves. (C) Time course of rhlAB expression was measured in swarming assays using the P_rhlABGFP reporter fusion and compared with constitutive GFP expression. The pictures shown use pseudocolor to highlight the fluorescence level. (D) The P_rhlABGFP expression was quantified by image analysis and normalized relatively to constitutive expression to confirm that the delay in rhlAB expression observed in liquid culture (panel B) occurs also in the swarming assay.