Abstract

The study of bacterial cell biology is limited by difficulties in visualizing cellular structures at high spatial resolution within their native milieu. Here, we visualize Bacillus subtilis sporulation using cryo-electron tomography coupled with cryo-focused ion beam milling, allowing the reconstruction of native-state cellular sections at molecular resolution. During sporulation, an asymmetrically-positioned septum generates a larger mother cell and a smaller forespore. Subsequently, the mother cell engulfs the forespore. We show that the septal peptidoglycan is not completely degraded at the onset of engulfment. Instead, the septum is uniformly and only slightly thinned as it curves towards the mother cell. Then, the mother cell membrane migrates around the forespore in tiny finger-like projections, whose formation requires the mother cell SpoIIDMP protein complex. We propose that a limited number of SpoIIDMP complexes tether to and degrade the peptidoglycan ahead of the engulfing membrane, generating an irregular membrane front.

Data availability

The authors have created a library of B. subtilis tomograms accessible at: villalab.ucsd.edu/research/engulfment. We have also deposited three representative tilt-series to Electron Microscopy Data Bank (EMDB) in the form of 4x binned tomograms. The IDs are EMD-20335, EMD-20336, EMD-20337 for Figure 1D,F,H respectively.

The following data sets were generated

Article and author information

Author details

  1. Kanika Khanna

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-7150-0350
  2. Javier Lopez-Garrido

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
  3. Ziyi Zhao

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
  4. Reika Watanabe

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0002-7427-7702
  5. Yuan Yuan

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
  6. Joseph Sugie

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    Competing interests
    The authors declare that no competing interests exist.
  7. Kit Pogliano

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    For correspondence
    kpogliano@ucsd.edu
    Competing interests
    The authors declare that no competing interests exist.
  8. Elizabeth Villa

    Division of Biological Sciences, University of California, San Diego, La Jolla, United States
    For correspondence
    evilla@ucsd.edu
    Competing interests
    The authors declare that no competing interests exist.
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0003-4677-9809

Funding

National Institute of Health's Director's New Innovator Award (1DP2GM123494)

  • Elizabeth Villa

National Institutes of Health (RO1-GM057045)

  • Kit Pogliano
  • Elizabeth Villa

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

  1. Tâm Mignot, CNRS-Aix Marseille University, France

Version history

  1. Received: January 29, 2019
  2. Accepted: July 4, 2019
  3. Accepted Manuscript published: July 8, 2019 (version 1)
  4. Version of Record published: August 6, 2019 (version 2)

Copyright

© 2019, Khanna et al.

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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  1. Kanika Khanna
  2. Javier Lopez-Garrido
  3. Ziyi Zhao
  4. Reika Watanabe
  5. Yuan Yuan
  6. Joseph Sugie
  7. Kit Pogliano
  8. Elizabeth Villa
(2019)
The molecular architecture of engulfment during Bacillus subtilis sporulation
eLife 8:e45257.
https://doi.org/10.7554/eLife.45257

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https://doi.org/10.7554/eLife.45257

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