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Mol Microbiol. 2018 May;108(3):319-329. doi: 10.1111/mmi.13938. Epub 2018 Mar 24.

Cryo-electron tomography analyses of terminal organelle mutants suggest the motility mechanism of Mycoplasma genitalium.

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Buchmann Institute for Molecular Life Sciences and Institute of Biophysics, Goethe University Frankfurt, Max-von-Laue Str. 15, Frankfurt 60438, Germany.
Departament de Bioquímica i Biologia Molecular and Institut de Biotecnologia i Biomedicina, Universitat Autònoma de Barcelona, Cerdanyola del Vallès 08193, Spain.
Faculty of Biological Sciences & FIAS, Goethe University Frankfurt, Ruth-Moufang-Straße 1, Frankfurt 60438, Germany.


The terminal organelle of Mycoplasma genitalium is responsible for bacterial adhesion, motility and pathogenicity. Localized at the cell tip, it comprises an electron-dense core that is anchored to the cell membrane at its distal end and to the cytoplasm at its proximal end. The surface of the terminal organelle is also covered with adhesion proteins. We performed cellular cryoelectron tomography on deletion mutants of eleven proteins that are implicated in building the terminal organelle, to systematically analyze the ultrastructural effects. These data were correlated with microcinematographies, from which the motility patterns can be quantitatively assessed. We visualized diverse phenotypes, ranging from mild to severe cell adhesion, motility and segregation defects. Based on our observations, we propose a double-spring ratchet model for the motility mechanism that explains our current and previous observations. Our model, which expands and integrates the previously suggested inchworm model, allocates specific functions to each of the essential components of this unique bacterial motility system.

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