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 mobi le which were obtained by UV irradiation. They were identified by their abn ormal colony shapes in 0.1% agar medium. snowing a reduced number of satell ite colonies compared to the wild-type. A total of ten mutants were isolate d based on their colony phenotype. Using dark-field and electron microscopy , two classes of mutants, group I and group II, were defined. Cells of grou p I mutants had irregular, flexible and sometimes elongated head-like struc tures and showed a tendency to aggregate. Neither binding to glass nor glid ing 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 glidi ng speed was 20% faster than that of wild-type cells. Three of the ten muta nts remained unclassified. Mutant m6 had a reduced binding activity to glas s and a reduced gliding motility with 50% of the speed of the wild-type str ain. The ability of wild-type and mutant colonies to adsorb erythrocytes wa s found to correlate with the binding activity required for gliding, indica ting that mycoplasma gliding depends on cytadherence-associated components. Finally, the ability to form microcolonies on surfaces was shown to correl ate with the gliding activity, suggesting a certain role of gliding motilit y in the parasitic life-cycle of mycoplasmas.