A minimized motile machinery for Mycoplasma genitalium

Abstract

SummaryThe cell wall-less bacterium Mycoplasma genitalium uses specialized adhesins located at the terminal organelle to adhere to host cells and surfaces. The terminal organelle is a polar structure protruding from the cell body that is internally supported by a cytoskeleton and also has an important role in cell motility. We have engineered a M. genitalium null mutant for MG491 protein showing a massive downstream destabilization of proteins involved in the terminal organelle organization. This mutant strain exhibited striking similarities with the previously isolated MG_218 null mutant strain. Upon introduction of an extra copy of MG_318 gene in both strains, the amount of main adhesins P140 and P110 dramatically increased. These strains were characterized by microcinematography, epifluorescence microscopy and cryo-electron microcopy, revealing the presence of motile cells and filaments in the absence of many proteins considered essential for cell adhesion and motility. These results indicate that adhesin complexes play a major role in the motile machinery of M. genitalium and demonstrate that the rod element of the cytoskeleton core is not the molecular motor propelling mycoplasma cells. These strains containing a minimized motile machinery also provide a valuable cell model to investigate the adhesion and gliding properties of this human pathogen.

Structural Study of MPN387, an Essential Protein for Gliding Motility of a Human-Pathogenic Bacterium, Mycoplasma pneumoniae

“…The force generated in the bowl complex may be transmitted through MPN387 to the paired plates. This hypothesis is consistent with the recent observation that the lack of HMW2 decreased the gliding speed by 112-fold (41). In the absence of HMW2, the force generated around the bowl complex may still be transmitted to the P1 adhesin much less efficiently than in the presence of HMW2, possibly through a distortion of the whole machinery.…”

The Variable Internal Structure of the Mycoplasma penetrans Attachment Organelle Revealed by Biochemical and Microscopic Analyses: Implications for Attachment Organelle Mechanism and Evolution

“…In contrast to M. pneumoniae, the M. penetrans AO consists solely of material whose lack of obvious organization is more reminiscent of the lucent area of M. pneumoniae than the core. Because both AOs, one with a core and one without, function in adherence and motility, it is possible that the core itself is dispensable for these functions in M. pneumoniae, as suggested previously (23,59), although this assertion is in opposition to some models (35,58). Therefore, we propose that the less organized material, constituting the ribosome-excluding zone in M. pneumoniae and perhaps the entire AO interior in M. penetrans, is the principal organizer of the AO, driving the concentration and organization of adhesins at the AO in both species and leaving motility to be carried out directly by adhesins with motor properties, as described for the more distantly related M. mobile (37).…”

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

“…S8). The ΔMG_491 strain has minimal motility over the whole cell population, with a fraction of the cells, including the cell fragments containing only the EDC, being motile but extremely slow (gliding speed below 1% of the wild‐type) as previously seen (Garcia‐Morales et al ., ). This is in agreement with a previously characterized mutant of M. pneumoniae where terminal organelle detachments were frequently observed in a mutant lacking the homolog of MG491 (P41) (Hasselbring and Krause, ).…”

“…This conclusion is based on the phenotype of the ΔMG_491 strain which had an assembled NAP layer but lacked the wheel component and was not motile. The EDC rod was interchangeable with the terminal button, to some extent, and one of them needed to be present for motility as also observed previously (Garcia‐Morales et al ., ). Lastly, the wheel complex had an intriguing role.…”

“…We propose the following roles for the individual components of the terminal organelle: (i)The NAPs are responsible for adhesion, may diffuse on the cell surface, and bind to the sialic acid‐derived compounds of the substrate (Kasai et al ., ), but do not generate movement individually. (ii)The terminal button attaches the rod to the cell surface and acts as the first ‘spring’ in the double‐spring ratchet model. This is justified since cells can still move when the rod is absent, just by the presence of the NAPs, terminal button and the wheel complex (Garcia‐Morales et al ., ). (iii)The wheel acts as a hybrid ratchet that connects and stabilizes the rod to the membrane; then creates a boundary between the cytoplasm and the terminal organelle; and finally, through centering the EDC, controls the directionality and regulates the efficiency of the ratchet, ranging from very inefficient (no movement) to efficient (at wild‐type speeds or theoretically even faster). (iv)The rod connects the terminal button to the wheel complex and acts as the second and main ‘spring’ in the double‐spring ratchet model. There is already data available supporting the function of the rod as a spring, although the dynamic (time‐dependent) changing of the spacing of the rod cannot be seen in the cryo‐ET images, since they are static.…”