Oxidative stress induced in E. coli by the human antimicrobial peptide LL-37
(A) Phase contrast and green fluorescence snapshots of single E. coli cell expressing periplasmic GFP in aerobic growth conditions, following addition of 4 μM LL-37 (the 6-hr aerobic MIC) with 5 nM Sytox Green. Times in minutes after injection of LL-37 at t = 0. (B) Time dependence of cell length (from phase contrast images) and total GFP and Sytox green fluorescence intensity for the cell shown in (A). Time of outer membrane permeabilization (OMP) and cytoplasmic membrane permeabilization (CMP) as shown. The initial decrease of fluorescence is due to loss of GFP from the periplasm to the surroundings. The subsequent burst of fluorescence is due to access of Sytox green to the cytoplasm upon CM permeabilization. (C) Cumulative distribution function (CDF) of the fraction of cells that have undergone CM permeabilization (onset of Sytox green fluorescence) vs time after the injection of 4 μM LL-37. Comparison for growth in aerobic respiration, anaerobic respiration using NO3–, and fermentation.