Intracellular levels and activity of PvdS, the major iron starvation sigma factor of Pseudomonas aeruginosa

Mol Microbiol. 2008 Jan;67(1):213-27. doi: 10.1111/j.1365-2958.2007.06051.x. Epub 2007 Nov 27.

Abstract

In Pseudomonas aeruginosa the iron starvation sigma factor PvdS directs the transcription of pyoverdine and virulence genes under iron limitation. PvdS activity is modulated by pyoverdine through the surface signalling cascade involving the FpvA receptor and the inner membrane-spanning sensor FpvR. To gain insight into the molecular mechanisms enabling PvdS to compete with the major sigma RpoD for RNA polymerase (RNAP) binding, we determined the intracellular levels of RNAP, RpoD and PvdS in P. aeruginosa PAO1, and the effect of pyoverdine signalling on PvdS activity. Under iron limitation, P. aeruginosa contains 2221 and 933 molecules of RNAP and RpoD per cell respectively. PvdS attains 62% of RpoD levels. The high PvdS content is partly offset by retention of 30% of PvdS on the membrane, lowering the concentration of cytosolic PvdS to 45% of RpoD levels. RNAP purification from iron-starved P. aeruginosa cells demonstrated that PvdS-RNAP is poorly represented compared with RpoD-RNAP (1 and 27% of total RNAP respectively). Pyoverdine signalling does not affect the PvdS cellular content but facilitates PvdS release from the membrane, increasing its cytosolic concentration from 35% in both pvdF and fpvA signalling mutants to 70% in the wild type and 83% in the fpvR mutant.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Outer Membrane Proteins / genetics
  • Bacterial Outer Membrane Proteins / metabolism
  • Bacterial Proteins / analysis
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • DNA-Directed RNA Polymerases / isolation & purification
  • DNA-Directed RNA Polymerases / metabolism
  • Gene Expression Regulation, Bacterial
  • Genes, Reporter
  • Holoenzymes / metabolism
  • Intracellular Space / metabolism*
  • Iron / metabolism*
  • Oligopeptides / metabolism
  • Pseudomonas aeruginosa / genetics
  • Pseudomonas aeruginosa / metabolism*
  • Sigma Factor / analysis
  • Sigma Factor / genetics
  • Sigma Factor / metabolism*

Substances

  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • FpvA protein, Pseudomonas aeruginosa
  • Holoenzymes
  • Oligopeptides
  • PvdS protein, Pseudomonas aeruginosa
  • Sigma Factor
  • rpoDA protein, Pseudomonas aeruginosa
  • pyoverdin
  • Iron
  • DNA-Directed RNA Polymerases