Identification of a novel gene, fimV, involved in twitching motility in Pseudomonas aeruginosa

Transposon mutagenesis was used to identify a new locus required for twitch ing motility in Pseudomonas aeruginosa. Four Tn5-B21 mutants which lacked t witching 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 structu re. 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-fimb riated bacteria Neisseria gonorrhoeae, Neisseria meningitidis, Legionella p neumophila and Vibrio cholerae, but not in those of other bacteria which la ck type IV fimbriae, A fimV homologue was also found in the genome sequence of Shewanella putrefaciens, along with many other homologues of type IV fi mbrial 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 result ed in an unusual phenotype where the cells were massively elongated and mig rated 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 a ssembly of the type IV fimbrial structure and machinery.