Low-Molecular Thiols as a Factor Improving the Sensitivity of Escherichia coli Mutants with Impaired Synthesis ADP-Heptose to Antibiotics

Low molecular weight thiols as glutathione and cysteine are an important part of the cell’s redox regulation system. Previously, we have shown that inactivation of ADP-heptose synthesis in Escherichia coli during gmhA deletion induces the oxidative stress. It is accompanied by rearrangement of thiol homeostasis and increased sensitivity to antibiotics. In our study, we found that restriction of cysteine metabolism (∆cysB and ∆cysE) and inhibition of glutathione synthesis (∆gshAB) lead to a decrease in the sensitivity of the ∆gmhA mutant to antibiotics but not to its expected increase. At the same time, blocking of the export of cysteine (∆eamA) or increasing the of the import (P_tet-tcyP) into cells of oxidized form of cysteine -cystine leads to an even greater increase in the sensitivity of gmhA-deleted cells to antibiotics. In addition, there is no correlation between the cytotoxic effect of antibiotics and the level of reactive oxygen species (ROS), the total pool of thiols or the viability of the initial cell population. However, a correlation between the sensitivity to antibiotics and the level of oxidized glutathione in cells was found in our study. Apparently, a decrease in the content of low molecular weight thiols saves NADPH equivalents and limits the processes of protein redox modification. It leads to increasing of resistance of the ∆gmhA strain to antibiotics. On the contrary, an increase in low molecular weight thiols levels requires a greater expenditure of cell resources, leads to an increase in oxidized glutathione and induces to greater increase in sensitivity of the ∆gmhA strain to antibiotics.