Gliding mutants of Mycoplasma mobile: relationships between motility and cell morphology, cell adhesion and microcolony formation.

The present study characterizes gliding motility mutants of Mycoplasma mobile which were obtained by UV irradiation. They were identified by their abnormal colony shapes in 0.1% agar medium, showing a reduced number of satellite colonies compared to the wild-type. A total of ten mutants were isolated based on their colony phenotype. Using dark-field and electron microscopy, two classes of mutants, group I and group II, were defined. Cells of group I mutants had irregular, flexible and sometimes elongated head-like structures and showed a tendency to aggregate. Neither binding to glass nor gliding motility was observed in these mutants. Cells of group II mutants were rather spherical in shape, with the long axis reduced to 80% and the short axis enlarged to 120% of that of wild-type cells, respectively. Their gliding speed was 20% faster than that of wild-type cells. Three of the ten mutants remained unclassified. Mutant m6 had a reduced binding activity to glass and a reduced gliding motility with 50% of the speed of the wild-type strain. The ability of wild-type and mutant colonies to adsorb erythrocytes was found to correlate with the binding activity required for gliding, indicating that mycoplasma gliding depends on cytadherence-associated components. Finally, the ability to form microcolonies on surfaces was shown to correlate with the gliding activity, suggesting a certain role of gliding motility in the parasitic life-cycle of mycoplasmas.