Fig. 2: ObgE* toxicity in E. coli L-forms hints at an effect of ObgE* on the outer membrane.

A ObgE* remains toxic in E. coli L-forms that are devoid of peptidoglycan. E. coli pBAD33Gm (Vector), pBAD33Gm-obgE (ObgE), or pBAD33Gm-obgE* (ObgE*) were grown on agarose pads that contain arabinose, the inducer of obgE(*) expression, and fosfomycin, which triggers the transition into the L-form state. Snapshot images of time-lapse microscopy recordings are shown. B Quantitative analysis of these time-lapse images reveals that ObgE* strongly inhibits L-form proliferation. The number of successful L-form divisions was recorded and normalized to the number of intact L-forms present in the field of view. Data are represented as the mean ± SEM, number of biological replicates n = 3, where each repeat contains > 40 L-forms. C, D Time-lapse images of single (C) or dividing (D) E. coli cells that express obgE* are shown as they transition into the L-form stage and subsequently undergo cell lysis that proceeds in two distinct steps. E Time-lapse images of E. coli L-forms that express obgE* and contain a blue periplasmic and red cytoplasmic marker reveals how ObgE* triggers two-stage L-form lysis. ObgE* initially causes rupture of the outer membrane and loss of periplasmic content, while the second stage of lysis corresponds to the loss of inner membrane integrity and cytoplasmic content.