Pseudomonas aeruginosa LasR-deficient mutants have increased methylglyoxal and hydrogen peroxide sensitivity due to low intracellular glutathione

The electrophile methylglyoxal (MG) is produced by microorganisms and host cells through central metabolic pathways. MG is a highly reactive electrophile, so it must be rapidly detoxified to prevent damaging modifications to macromolecules. Pseudomonas aeruginosa, a pathogen of concern due to its ability develop multidrug resistance, causes many types of infections that have been associated with elevated MG levels, including cystic fibrosis (CF). P. aeruginosa isolates commonly have mutations that lead to LasR loss-of-function (LasR-) and we found that lasR mutations confer sensitivity to MG in multiple strain backgrounds. LasR-strains have increased activity of the CbrAB two-component system which represses Crc regulation of metabolism. Here, we show that higher CbrAB activity and low Crc activity renders cells sensitive to MG. We found that P. aeruginosa LasR-strains are more sensitive to MG and have lower intracellular reduced glutathione (GSH) compared to their LasR+ comparators. Consistent with published reports, mutants lacking gloA3, which encodes a MG-glyoxalase, and mutants lacking GSH biosynthesis enzymes (gshA or gshB) were sensitive to MG. Exogenous GSH rescued MG sensitivity in LasR-strains and gshA or gshB mutants, but not in a gloA3 mutant strain. We propose that low GSH levels in LasR-strains contribute to increased sensitivity to MG and H2O2. SignificanceMethylglyoxal is a highly reactive metabolite that is detected in various disease states, including those where Pseudomonas aeruginosa is present and MG resistance requires the glutathione-dependent glyoxalase enzyme GloA3 enzyme. This study reveals that P.aeruginosa strains with LasR mutations, which are commonly found in clinical isolates, are more sensitive to methylglyoxal (MG) and hydrogen peroxide due to lower intracellular glutathione levels and high activity of the CbrAB-Crc regulatory pathway. This could be significant for understanding the selective pressures that drive P. aeruginosa evolution in infection sites, as well as a better understanding of LasR-strain metabolism in infections such as those associated with cystic fibrosis.