Figure 6.

Characterization of the migration response of CoMot-S and CoMot-S+ cells in a 3OC6HSL gradient shows directional movement of cells away from a 3OC6HSL source: (a) Illustration of 3OC6HSL-dependent motA expression in the CoMot-S strain. Expression of motA is under the control of the P_esaS promoter. esaR is constitutively expressed from a σ⁷⁰-dependent promoter and activates expression from P_esaS. In the absence of 3OC6HSL, motA is expressed and motility is restored in the ΔmotA cells. Following addition of 3OC6HSL, EsaR unbinds from P_esaS. motA expression decreases and the cells become non-motile. (b) 3OC6HSL gradients were established by adding 0–53 μg of 3OC6HSL on a Whatmann membrane and allowing it to diffuse for 8 h. 10 μM of 3OC6HSL would be the final concentration if 53 µg of 3OC6HSL diffused uniformly through the plate. CoMot-S (ΔmotA transformed with plasmids containing P_esaS-motA and P_σ70-esaR) or CoMot-S+ (ΔmotA transformed with plasmids containing P_esaS-motA and P_σ70-esaR-D91G) cells were then inoculated at the centre of the plate. Representative plate images obtained after 24 h of incubation at 30 °C. (c) Forward migration distance was measured as the distance between the inoculation point and the visible edge of migration of cells up the signal gradient after 24 h of incubation at 30 °C. Error bars represent one standard deviation from the mean forward migration distance of three biological replicates.