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Complex regulations of swarming and surfing motilities in pseudomonas aeruginosa Yeung, Amy Tsz Yan


To investigate how the complex adaptation process of swarming is regulated, a P. aeruginosa PA14 transposon mutant library was screened for mutants defective in swarming. As a result, 233 mutants exhibiting alterations in swarming phenotypes were identified and 35 of these genes encoded for regulators. Only a few of these regulatory mutants showed significant defects in the production of type IV pili, flagella, or rhamnolipid, each of which is known to be involved in swarming, suggesting that the majority of these regulators control other factors important in swarming. One regulatory mutant with a mutation in the cbrA gene was chosen to be investigated in detail. In addition to swarming motility and carbon source utilization, the sensor kinase CbrA was shown to play regulatory roles in other virulence and virulence-related processes of Pseudomonas, including biofilm formation, cytotoxicity, and antibiotic resistance. Microarray analysis revealed hundreds of dysregulated genes in the cbrA mutant that might contribute to the virulence and virulence-related phenotypes observed in the mutant. Phenotypic and genetic analyses of a cbrB mutant suggested that CbrA modulated swarming, biofilm formation, and cytotoxicity via the CbrB response regulator and that the CrcZ small RNA and the Crc protein are likely downstream of this two-component regulator. Little was known about the mode of motility P. aeruginosa uses to colonize the lungs of patients with cystic fibrosis (CF) since the viscous lung environment in vivo is influenced by mucin in the mucous. To investigate this, the nutritional composition of the CF sputum was mimicked using plates containing synthetic CF medium (SCFM) with mucin. Addition of small amounts (0.05%) of mucin to SCFM-swimming agar led P. aeruginosa to undergo accelerated motility on the surface of the agar. The surface motility colonies in the presence of mucin were circular with a green center surrounded by a thicker white edge. In contrast to swarming, bacterial cells at the edge of the mucin-promoted motility zone appeared piled up and lacked flagella. Using genetic and microscopic methods, it was demonstrated that mucin might be promoting a modified form of swarming or likely a new form of surface motility, termed “surfing”.

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