Force and Velocity of Mycoplasma mobile Gliding

Abstract

The effects of temperature and force on the gliding speed of Mycoplasma mobile were examined. Gliding speed increased linearly as a function of temperature from 0.46 m/s at 11.5°C to 4.0 m/s at 36.5°C. A polystyrene bead was attached to the tail of M. mobile using a polyclonal antibody raised against whole M. mobile cells. Cells attached to beads glided at the same speed as cells without beads. When liquid flow was applied in a flow chamber, cells reoriented and moved upstream with reduced speeds. Forces generated by cells at various gliding speeds were calculated by multiplying their estimated frictional drag coefficients with their velocities relative to the liquid. The gliding speed decreased linearly with force. At zero speed, the force measurements extrapolated to 26 pN at 22.5 and 27.5°C. At zero force, the speed extrapolated to 2.3 and 3.3 m/s at 22.5 and 27.5°C, respectively-the same speeds as those observed for free gliding cells. Cells attached to beads were also trapped by an optical tweezer, and the stall force was measured to be 26 to 28 pN (17.5 to 27.5°C). The gliding speed depended on temperature, but the maximum force did not, suggesting that the mechanism is composed of at least two steps, one that generates force and another that allows displacement. Other implications of these results are discussed.Mycoplasmas are parasitic bacteria with a small genome and no peptidoglycan layer (27). Several mycoplasma species have a distinct cell polarity characterized by a protruding membrane extension, the attachment organelle (27). They are able to attach to and glide on glass, plastic, and eukaryotic cell surfaces, always moving in the direction of the organelle (19). The gliding mechanism is unknown. Mycoplasmas do not have any appendages such as flagella or pili (19) or any genes obviously related to motility, including motor proteins such as myosin or kinesin (7, 10, 13). However, a transmembrane protein associated with a cytoskeleton-like structure has been shown to be necessary for glass binding in Mycoplasma pneumoniae (22).Mycoplasma mobile, isolated from a fish gill organ, has a conical cell structure, with the attachment organelle at the apex of the cone. It glides up to four cell lengths per second (2.5 m/s) in the direction of the apex, which is designated as a head-like structure (30). However, little is known about force generation (28,29). In this study, to characterize its gliding motility, we attached a bead to the tail end of M. mobile and measured the gliding force as a function of speed using viscous flow and an optical tweezer. MATERIALS AND METHODSCultivation. M. mobile strain 163K (ATCC 43663) was grown as described previously (25).Measurements of gliding speed. M. mobile cells in a culture at an optical density at 600 nm of 0.03 to 0.1 were collected by centrifugation at 10,000 ϫ g for 4 min at room temperature and resuspended in a fivefold-smaller volume of medium. A 5-l aliquot was sealed between a coverslip and a slide within a thin ring of Apiezon M grease (Apiezon Products, L...

Spike Structure at the Interface between GlidingMycoplasma mobileCells and Glass Surfaces Visualized by Rapid-Freeze-and-Fracture Electron Microscopy

“…Previously, we studied the movement of cells attached with beads on surfaces (20,21) and cells having an elongated headlike protrusion (22). Based on these studies, we predicted that the force of movement is generated around the head-like protrusion, and indeed, the observed distribution of spikes is consistent with this prediction.…”

“…At all stages of growth, M. mobile glides smoothly and continuously on glass at an average speed of 2.0 to 4.5 m/s, or about 3 to 7 times the length of the cell per s (27), exerting a force of up to 27 piconewtons (pN) (20,21). These distinct characteristics enabled detailed analyses of gliding (6,(20)(21)(22)(26)(27)(28) and isolation of gliding mutants that were characterized by reduced or deficient gliding or enhanced speed (23,28). …”

“…An individual M. mobile cell generates a rather large force of up to 27 pN, which has raised speculation that the cell's binding and gliding machinery is anchored to an stationary structure rather than floating freely in the membrane (20). Indeed, it has been proposed that the electron-dense core observed in M. pneumoniae may support its attachment organelle and serve as scaffolding for that species' binding and gliding machinery (16a, 25a).…”

Cytoskeletal “jellyfish” structure of Mycoplasma mobile

“…mobile, isolated from the gills of a freshwater fish in the early 1980s, is a fast-gliding mycoplasma (12)(13)(14)(15)(16). It glides smoothly and continuously on glass at an average speed of 2.0 to 4.5 m/s, or three to seven times the length of the cell per second, exerting a force of up to 27 piconewtons (pN).…”

Mycoplasma takes a walk

“…Attachment to the glass and cell displacement occur at the neck, with the head serving as the leading end of the cell (11). The cell does not reverse directions, and it exerts a substantial force of 27 pN during gliding (12). Three major approaches have been used to identify cellular proteins involved in cell motility and attachment.…”