The ability to produce outer membrane projections in the form of tubular membrane extensions (MEs) and membrane vesicles (MVs) is a widespread phenomenon among diderm bacteria. Despite this, our knowledge of the ultrastructure of these extensions and their associated protein complexes remains limited. Here, we surveyed the ultrastructure and formation of MEs and MVs, and their associated protein complexes, in tens of thousands of electron cryo-tomograms of ~90 bacterial species that we have collected for various projects over the past 15 years (Jensen lab database), in addition to data generated in the Briegel lab. We identified outer MEs and MVs in 13 diderm bacterial species and classified several major ultrastructures: (1) tubes with a uniform diameter (with or without an internal scaffold), (2) tubes with irregular diameter, (3) tubes with a vesicular dilation at their tip, (4) pearling tubes, (5) connected chains of vesicles (with or without neck-like connectors), (6) budding vesicles and nanopods. We also identified several protein complexes associated with these MEs and MVs which were distributed either randomly or exclusively at the tip. These complexes include a secretin-like structure and a novel crown-shaped structure observed primarily in vesicles from lysed cells. In total, this work helps to characterize the diversity of bacterial membrane projections and lays the groundwork for future research in this field.

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Notes/Citation Information

Published in eLife, v. 10, e73099.

© 2021, Kaplan et al.

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

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Funding Information

National Institutes of Health (R35 GM122588): Grant J Jensen

California Institute of Technology (Baxter postdoctoral fellowship): Mohammed Kaplan

Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO OCENW.GROOT.2019.063): Ariane Briegel

National Institutes of Health (P20 GM130456): Carrie L Shaffer

Nederlandse Organisatie voor Wetenschappelijk Onderzoek (184.034.014): Ariane Briegel

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