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Unitary step of gliding machinery in Mycoplasma mobile

Significance The mechanism of movement of bacteria shows extensive diversity, and some bacteria glide on the substrate surface via an unknown process. Mycoplasma mobile is one of the fastest, exhibiting smooth gliding movement with a speed of 2.0–4.5 µm/s. By applying the modified in vitro ghost model of Mycoplasma mobile to high precision colocalization microscopy, steps of the regular size, ∼70 nm, were detected for the first time in bacteria, to our knowledge. The binding target of the gliding machinery, sialylated oligosaccharides, was expected to be randomly oriented on the surface and, thus, our results suggest that the machinery can drive the steps with a cycle of attachment and detachment even if there is no periodic structure on the substrate. Among the bacteria that glide on substrate surfaces, Mycoplasma mobile is one of the fastest, exhibiting smooth movement with a speed of 2.0–4.5 μm⋅s−1 with a cycle of attachment to and detachment from sialylated oligosaccharides. To study the gliding mechanism at the molecular level, we applied an assay with a fluorescently labeled and membrane-permeabilized ghost model, and investigated the motility by high precision colocalization microscopy. Under conditions designed to reduce the number of motor interactions on a randomly oriented substrate, ghosts took unitary 70-nm steps in the direction of gliding. Although it remains possible that the stepping behavior is produced by multiple interactions, our data suggest that these steps are produced by a unitary gliding machine that need not move between sites arranged on a cytoskeletal lattice.