J.A. Williams, S. Abad Herrera, S. Heinrich, F.M.L. Peeters, N. Lupilov, J.E. Bandow, T. Günther Pomorski, L.R. Knoke (2026).
Modifications of the bacterial cell envelope by neutrophil-derived oxidants.
Free Radical Biology and Medicine 249(Supplement 1): S9
doi: 10.1016/j.freeradbiomed.2026.05.048
Neutrophils, specialized in phagocytosis orchestrate a coordinated attack on engulfed bacteria, including the highly toxic hypochlorous acid (HOCl) and HOCl-derived chloramines like N-chlorotaurine (NCT). In host-pathogen interactions, the bacterial envelope will naturally be the first target of these oxidants. Here, we examined occurrence of N-chloramines in the bacterial cell envelope, their biological activity, and impact on membrane integrity. Using a chemical probe for N-chloramines we demonstrated that HOCl forms N-chloramines with amino residues in some membrane lipids and lipopolysaccharides in E. coli cell envelopes. In contrast, NCT only showed poor chlorinating activity in vitro. N-chlorinated model membranes efficiently oxidized the redox-sensitive protein roGFP2, suggesting that cell envelope N-chloramines might disrupt cellular thiol homeostasis. While relatively stable in vitro, they are significantly less stable in living cells indicating both, active detoxification and reactivity with other cellular components. To study the effects of HOCl and NCT on membrane integrity, we used content leakage assays with model membranes and applied fluorescent probes for membrane permeability and potential measurements in E. coli cells. Bacteria actively take up taurine through ABC transporters (TauABC and SsuABC). To elucidate the role of taurine importers in NCT susceptibility, we monitored the growth of E. coli tauB and ssuB deletion mutants in the presence of NCT. Lack of TauB increased NCT resistance, suggesting that NCT toxicity depends on interaction with both, the bacterial cell envelope and cytosolic components. Overall, we propose that envelope N-chloramines are involved in modulating host immune cells and contribute to bacterial killing.