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Pseudomonas aeruginosa twitching motility requires vfr, but not the las or rhl quorum sensing systems

, : Pseudomonas aeruginosa twitching motility requires vfr, but not the las or rhl quorum sensing systems. Abstracts of the General Meeting of the American Society for Microbiology 101: 85

Vfr, a homolog of Escherichia coli cyclic AMP receptor protein, has been shown to regulate quorum sensing (via control of lasR transcription), exotoxin A production and regA transcription. During a transposon library screen for non-twitching P. aeruginosa mutants we identified an insertion in vfr. We confirmed that vfr was required for twitching motility by creating additional vfr knockouts in P. aeruginosa and demonstrating their inability to twitch. Furthermore, non-twitching vfr mutants could be complemented with wildtype vfr. Although vfr has not been previously implicated in twitching motility it has been reported that rhlI and lasI quorum sensing mutants of P. aeruginosa have impaired twitching motility (Glessner et. al (1999), J Bac 181, 1623-9). To investigate if Vfr indeed controlled twitching motility via the quorum sensing pathway in P. aeruginosa we constructed knockouts of lasI, rhlI, lasR, rhlR, lasR/rhlR, lasI/rhlI, lasRI, rhlRI and lasRI/rhlRI in both PAO1 and PAK strains: all mutants were identical to wildtype by twitching stab assay and microscopy. One possible explanation for the phenotypic discrepancy between our mutants and those of Glessner et. al is the occurrence of secondary site mutation(s) in the latter. Intriguingly, a proportion of our lasI and rhlI mutants spontaneously developed defects in twitching motility. Attempts to complement the predicted secondary site mutation in defective twitching lasI mutants succeeded using wildtype vfr. We amplified, cloned and sequenced vfr from wildtype and both twitching and defective twitching variants of our lasI mutant and identified a 15 nucleotide deletion in the latter. Our results indicate that vfr, but not the las or rhl quorum sensing systems, is required for twitching motility in P. aeruginosa.


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