An Escherichia coli Phosphotransferase System Modulates Methylglyoxal Resistance by Regulating Intracellular...

Methylglyoxal is a toxic aldehyde produced during cellular metabolism across all domains of life. To cope with methylglyoxal stress, Escherichia coli employs the glyoxalase detoxification pathway coupled with Kef-mediated potassium/proton antiport. However, the Kef system is protective only when extracellular potassium is well below concentrations typically found in mammalian hosts. The regulatory phosphotransferase system (PTS) that is historically known as the nitrogen-related PTS (PTS^Ntr) has previously been shown to modulate potassium homeostasis and other processes in E. coli. Here, we identified this regulatory PTS as a mediator of methylglyoxal resistance for potassium concentrations that are comparable to those encountered in the context of host colonization or infection. We found that loss of unphosphorylated PtsN increases survival in methylglyoxal, and that this depended on the potassium/proton antiporter YcgO, whose activity decreases intracellular potassium and pH. While cytoplasmic acidification has been hypothesized to underlie protection from methylglyoxal via potassium/proton antiport, our results suggest the effects of acidification and intracellular potassium cannot be easily separated. Loss of potassium import through Trk increased survival in methylglyoxal and decreased intracellular potassium with only a relatively small decrease in pH. Moreover, the addition of acetate, which acidifies the cytoplasm and protects cells from methylglyoxal, also decreased intracellular potassium. Our results demonstrate that for extracellular potassium levels relevant for host infection and colonization, PtsN modulates methylglyoxal resistance by regulating potassium transport, and that low intracellular potassium, in addition to acidification, could play a direct role in protecting against methylglyoxal stress.