Effects of low intracellular glutathione and CbrA-CbrB-Crc signaling on methylglyoxal sensitivity in Pseudomonas aeruginosa LasR-deficient mutants.

Pseudomonas aeruginosa, which causes many types of infections, often has loss-of-function mutations in the gene encoding LasR, a transcription factor involved in quorum sensing. Here, we report that LasR- strains are more sensitive to the electrophile methylglyoxal (MGO), which is produced by many cells, including those involved in immune defense. MGO, due to its high reactivity, must be rapidly detoxified to prevent the formation of damaging adducts on macromolecules. GloA3 is a GSH-dependent MGO glyoxalase involved in MGO detoxification, and we found that intracellular GSH levels were lower in ∆lasR strains, as measured by multiple methods. Furthermore, we show that exogenous GSH and GloA3 overexpression both enhance GloA3-dependent MGO resistance, particularly in a ∆lasR mutant. Previous reports suggest that one factor that contributes to the selection for LasR- strains is a growth advantage resulting from increased activity of the CbrAB two-component system, which lowers the Crc-mediated translational repression of many RNAs. Genetic data presented here suggest that low Crc activity leads to increased MGO sensitivity in LasR- strains but not through effects on GSH or GloA3. Together, these data suggest that LasR- strains are more sensitive to MGO due to multiple factors, including lower intracellular levels of GSH and decreased Crc activity, and that these factors may represent fitness trade-offs for LasR- strains.IMPORTANCEMethylglyoxal (MGO) is a highly reactive metabolite detected in various disease states, including those involving Pseudomonas aeruginosa. P. aeruginosa requires the glutathione-dependent glyoxalase enzyme GloA3 for MGO resistance. This study reveals that P. aeruginosa strains with mutations in the gene encoding the transcription factor LasR, commonly found in clinical isolates, are more sensitive to MGO due to lower intracellular glutathione levels and high activity of the CbrAB-Crc regulatory pathway. Thus, sensitivity to MGO and other electrophiles may represent a trade-off for P. aeruginosa in infections.