Qin, Jilong, Hong, Yaoqin, Vollmer, Waldemar, Morona, Renato, and Totsika, Makrina (2025) Disruptions in outer membrane-peptidoglycan interactions enhance bile salt resistance in O-antigen-producing E. coli. mBio. (In Press)

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Abstract

Bile salts (BS) are antimicrobials that disrupt bacterial cell membranes and induce oxidative stress. The gut bacterium Escherichia coli is naturally resistant to BS, including the model strain K12 MG1655 that produces a lipopolysaccharide (LPS) without O-antigen (OAg) on the cell surface. Paradoxically, we have previously shown that restoring a wild-type like LPS with attached OAg (MG1655-S) sensitizes E. coli K12 to exogenous BS. In this study, we investigate this phenomenon. We show that mutations causing truncation of the LPS core oligosaccharide render MG1655-S strains even more susceptible to BS compared to MG1655. These mutants phenocopy a K-12 MG1655-S ΔwaaL mutant, which is defective in OAg ligase, primarily due to periplasmic accumulation of the unligated lipid-linked UndPP-OAg. Through the characterization of BS-resistant suppressor mutants of MG1655-S ΔwaaL, we identify key genetic disruptions involved in resistance. Notably, we observed the highest BS resistance in strains with a weaker connection between the outer membrane (OM) and peptidoglycan (PG), including strains lacking the major OM-anchored, PG-binding proteins OmpA or Lpp. Expressing versions of OmpA and Lpp that lack PG-binding capacity also enhanced the BS resistance. Our data suggest that BS-induced stress in OAg-producing E. coli is due to the spatial constraints between OM and PG and that mutations disrupting OM–PG interactions alleviate this stress, thereby enhancing BS resistance. These findings provide new insights into a major challenge E. coli faces in the gut environment, where it needs to produce OAg for stable colonization and immune evasion while resisting the antimicrobial activity of BS.

Item ID:	87616
Item Type:	Article (Research - C1)
ISSN:	2150-7511
Copyright Information:	Copyright © 2025 Qin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.
Date Deposited:	03 Sep 2025 00:29
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