FIG 6 .

Growth competition between the wild-type strain and a mutant overexpressing MexAB-OprM in nitrate-free medium. The relative fitness between JFL30 and the wild-type strain was estimated by coculturing both strains and is represented as the percentage of mutant cells present at each time point (days). The absence of nitrate in the spent medium (solid line) produces a fitness cost in JFL30. However, the addition of nitrate to the medium partly reverts this cost. This result confirms the need for nitrate availability to avoid the fitness cost caused by overexpression of RND pumps. The figure shows the means and standard deviations from three different experiments.