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.
Transposon mutagenesis was used to identify a new locus required for twitching motility in Pseudomonas aeruginosa. Four Tn5-B21 mutants which lacked twitching motility and a fifth which exhibited impaired motility were found to map to the same KpnI restriction fragment at approximately 40 min on the P. aeruginosa genome. Cloning and sequencing studies showed that all five transposon insertions occurred within the same 2·8 kb ORF, which was termed fimV. The product of this gene has a putative peptidoglycan-binding domain, predicted transmembrane domains, a highly acidic C terminus and anomalous electrophoretic migration, indicating unusual primary or secondary structure. The P. aeruginosa genome also possesses a paralogue of fimV. Homologues of fimV were also found in the sequenced genomes of the other type-IV-fimbriated bacteria Neisseria gonorrhoeae, Neisseria meningitidis, Legionella pneumophila and Vibrio cholerae, but not in those of other bacteria which lack type IV fimbriae. A fimV homologue was also found in the genome sequence of Shewanella putrefaciens, along with many other homologues of type IV fimbrial genes, indicating that this bacterium is also likely to produce type IV fimbriae. Wild-type twitching motility was restored to fimV mutants by complementation in a dosage-dependent manner. Overexpression of fimV resulted in an unusual phenotype where the cells were massively elongated and migrated in large convoys at the periphery of the colony. It is suggested that FimV may be involved in remodelling of the peptidoglycan layer to enable assembly of the type IV fimbrial structure and machinery.