Mycoplasma takes a walk

The mechanism of movement of individual cells shows extensive diversity. In the Eukarya, ATP is the driving force for cell motility (1). In contrast, in the Bacteria and Archaea, the chemiosmotic pathway of energy transduction powers flagellar rotation. Depending on the species, either hydrogen or sodium ion flux results in cell movement. ATP does not directly participate in providing the energy needed for this type of motility (2). But some species of bacteria move by means other than flagellar-based motility. Do hydrogen or sodium gradients propel these organisms as well? In a recent issue of PNAS, Uenoyama and Miyata (3) directly showed that for a wall-less bacterial species, Mycoplasma mobile, intracellular ATP is the driving force for its relatively fast gliding along a glass surface. This is the second type of motility powered by ATP identified in bacteria, the first being the retraction of type IV pili as seen, for example, in Myxobacteria and Pseudomonas (4, 5).

Uenoyama and Miyata (3) used a multistep approach to reach this conclusion, but the essential experimental design was borrowed from eukaryotic cell biology. First, they isolated a spontaneously occurring mutant of M. mobile that can attach more efficiently to a glass surface than the wild type does. This mutant enabled them to assay the motility of a large number of cells. Second, using a procedure similar to that used by Gibbons and Gibbons (6) on sea urchin sperm, they rendered the membrane of gliding M. mobile cells permeable with a low concentration of the detergent Triton X-100. What remained were nonmotile ghosts that lacked DNA but still adhered to the glass. Finally, when incubated with ATP, the ghosts regained motility with speeds similar to untreated cells (≈2 μm/s). The results are striking, and the reader is urged to view the …