flhDC, but not fleQ, regulates flagella biogenesis in Azotobacter vinelandii, and is under AlgU and CydR negative control

Microbiology. 2008 Jun;154(Pt 6):1719-1728. doi: 10.1099/mic.0.2008/017665-0.


Azotobacter vinelandii is a nitrogen-fixing soil bacterium that undergoes differentiation to form cysts resistant to desiccation. Upon encystment, this bacterium becomes non-motile. As in enteric bacteria, motility in A. vinelandii occurs through the use of peritrichous flagella. Pseudomonas aeruginosa, a phylogenetically close relative of A. vinelandii, possesses a single polar flagellum. The FlhDC proteins are the master regulators of flagella and motility in enterobacteria, whereas FleQ is the master regulator in P. aeruginosa, and it is under AlgU (sigmaE) negative control. At present, nothing is known about the organization and expression of flagella genes in A. vinelandii. Here, we identified the flagella gene cluster of this bacterium. Homologues of the master regulatory genes flhDC and fleQ are present in A. vinelandii. Inactivation of flhDC, but not fleQ, impaired flagella biogenesis and motility. We present evidence indicating that a negative effect of the AlgU sigma factor on flhDC expression causes loss of motility in A. vinelandii, and that CydR (a homologue of Fnr) is under AlgU control and has a negative effect on flhDC expression. Taken together, these results suggest the existence of a cascade consisting of AlgU and CydR that negatively controls expression of flhDC; the results also suggest that the block in flagella synthesis under encystment conditions centres on flhDC repression by the AlgU-CydR cascade.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azotobacter vinelandii / genetics*
  • Azotobacter vinelandii / metabolism*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Binding Sites
  • Flagella / genetics
  • Flagella / metabolism*
  • Gene Expression Regulation, Bacterial*
  • Gene Silencing
  • Genes, Bacterial / genetics
  • Genetic Complementation Test
  • Genome, Bacterial / genetics
  • Molecular Sequence Data
  • Repressor Proteins / metabolism*
  • Sequence Alignment


  • Bacterial Proteins
  • CydR protein, Azotobacter vinelandii
  • Repressor Proteins