Truncation of type IV pilin induces mucoidy in Pseudomonas aeruginosa strain PAO579
Article first published online: 27 MAR 2013
© 2013 The Authors. Microbiology Open published by John Wiley & Sons Ltd.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Volume 2, Issue 3, pages 459–470, June 2013
How to Cite
MicrobiologyOpen 2013; 2(3): 459–470
- Issue published online: 7 JUN 2013
- Article first published online: 27 MAR 2013
- Manuscript Accepted: 26 FEB 2013
- Manuscript Revised: 25 FEB 2013
- Manuscript Received: 23 OCT 2012
- National Aeronautics and Space Administration West Virginia Space Grant Consortium
- Cystic Fibrosis Foundation. Grant Number: YU11G0
- NIH. Grant Numbers: P20RR016477, P20GM103434
- Graduate Student Researchers Program. Grant Numbers: NNX06AH20H, DAMRON10F0
- muc-23 ;
- pilA ;
- Pseudomonas aeruginosa
Pseudomonas aeruginosa is a Gram negative, opportunistic pathogen that uses the overproduction of alginate, a surface polysaccharide, to form biofilms in vivo. Overproduction of alginate, also known as mucoidy, affords the bacterium protection from the host's defenses and facilitates the establishment of chronic lung infections in individuals with cystic fibrosis. Expression of the alginate biosynthetic operon is primarily controlled by the alternative sigma factor AlgU (AlgT/σ22). In a nonmucoid strain, AlgU is sequestered by the transmembrane antisigma factor MucA to the cytoplasmic membrane. AlgU can be released from MucA via regulated intramembrane proteolysis by proteases AlgW and MucP causing the conversion to mucoidy. Pseudomonas aeruginosa strain PAO579, a derivative of the nonmucoid strain PAO1, is mucoid due to an unidentified mutation (muc-23). Using whole genome sequencing, we identified 16 nonsynonymous and 15 synonymous single nucleotide polymorphisms (SNP). We then identified three tandem single point mutations in the pilA gene (PA4525), as the cause of mucoidy in PAO579. These tandem mutations generate a premature stop codon resulting in a truncated version of PilA (PilA108), with a C-terminal motif of phenylalanine-threonine-phenylalanine (FTF). Inactivation of pilA108 confirmed it was required for mucoidy. Additionally, algW and algU were also required for mucoidy of PAO579. Western blot analysis indicated that MucA was less stable in PAO579 than nonmucoid PAO1 or PAO381. The mucoid phenotype and high PalgU and PalgD promoter activities of PAO579 require pilA108, algW, algU, and rpoN encoding the alternative sigma factor σ54. We also observed that RpoN regulates expression of algW and pilA in PAO579. Together, these results suggest that truncation in type IV pilin in P. aeruginosa strain PAO579 can induce mucoidy through an AlgW/AlgU-dependent pathway.