Figure 2.

Effect of MexL and growth phase on mexJK expression. The expression of mexK was determined by RT-qPCR in both PAO1 and ΔmexL strains at stationary and exponential phases of growth. Fold change regarding the level of expression of mexK in PAO1 at exponential growth phase is presented. As shown, lack of MexL highly increased mexK expression, indicating that, in agreement with previous reports [59,60], MexL is a negative regulator of mexJK. In addition, expression was higher at stationary growth phase in both strains, indicating that growth-phase regulation of mexK expression is independent of MexL. Values that are significantly different by an unpaired two-tail t-test are indicated by asterisks as follows: * p < 0.05; ** p < 0.01; **** p < 0.0001.