Molecular basis for bile sensitivity of Escherichia coli with defective LPS O-antigen assembly.

Stalled O-antigen biogenesis in Escherichia coli with defective LPS O-antigen assembly causes bile sensitivity by sequestering a lipid carrier, even when O-Ag never reaches the periplasm.

• Why it matters: Reports had claimed periplasmic O-Ag chains directly disrupt envelope integrity and drive bile sensitivity, but the mechanism and whether toxicity is inherent were unclear.
• What they did: The authors tested bile sensitivity in E. coli with disrupted WaaL function and also examined cases where O-Ag repeat units were trapped in the cytosol; they further suppressed sensitivity by disrupting OM–peptidoglycan interactions and by increasing lipid carrier availability.
• The result: They found bile sensitivity can be suppressed without requiring periplasmic O-Ag, and that stalled O-Ag chains limit lipid carrier for peptidoglycan synthesis, implying bile vulnerability reflects reduced lipid carrier availability rather than inherent periplasmic damage.

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