(A) Wild type E. coli (MG1655); ΔopgG (ΔmdoG; JW1035) and ΔopgH (ΔmdoH; JW1037), mutants blocked in periplasmic glucan synthesis were grown in LOS medium, and cells were treated in the presence or absence of either FeSO4, H2O2 or FeSO4+DP (dipyridyl) were analyzed for ROS by monitoring DCF fluorescence with flow cytometry. 