FIGURE 3.

Transfer messenger RNA deficiency protects from FQs lethal action. (A) Wild type R6 strain (wt) and its tmRNA deletion mutant (ΔssrA) were grown under different LVX concentrations in A+Y medium. Growth was followed by turbidity (OD_{620 nm}) in a TECAN infinite F200 plate reader at 37°C. (B) Percentage of survival to different FQs of wt, ΔssrA, the complemented strain containing the pROM-TM (ΔssrA(ssrA⁺)) and the ΔssrA containing the empty vector (ROM) at 37°C, and of wt at 30°C. Exponentially growing cells were treated with 5× MIC (as determined in Table 4) of LVX, ciprofloxacin (CPX), norfloxacin (NFX), or MOX for the times indicated. After incubation, survival was determined as described in Section “Materials and Methods.” (C) Accumulation of ROS in wt and ΔssrA upon addition of 5× MIC of LVX was measured as described in Section “Materials and Methods.” RFU; fluorescence units were divided by the number of viable cells and normalized to time zero and no antibiotic treatment condition. (D) Northern-blot showing tmRNA expression in wt, ΔssrA and ΔssrA(ssrA⁺). Bands corresponding to tmRNA and the control 5S rRNA are indicated by arrows. Northern-blots were performed as described (Acebo et al., 2012). Values (mean ± SD) of at least three independent experiments are shown. MIC values were determined in Table 4.