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

• Published in: Molecular microbiology 2018-05, Vol.108 (3), p.319-329
• Main Authors: Seybert, Anja, Gonzalez‐Gonzalez, Luis, Scheffer, Margot P., Lluch‐Senar, Maria, Mariscal, Ana M., Querol, Enrique, Matthaeus, Franziska, Piñol, Jaume, Frangakis, Achilleas S.
• Format: Article
• Language: English
• Subjects: Adhesion; Cell adhesion; Cell adhesion & migration; Clonal deletion; Cytoplasm; Deletion mutant; Motility; Mutants; Mycoplasma genitalium; Pathogenicity; Pathogens; Proteins; Tomography
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13938

Summary 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. Here, we visualized the terminal organelles of Mycoplasma genitalium deletion mutants by cellular cryoelectron tomography. Individual protein ensembles act as springs that periodically expand and retract, causing the cell tip to move forward, while the backward movement is constrained by other proteins that act as a ratchet. This work is a rich resource of cryoelectron tomograms that shed light into the molecular orchestration of the motility of this minimal genome organism.