An operon containing fumC and sodA encoding fumarase C and manganese superoxide dismutase is controlled by the ferric uptake regulator in Pseudomonas aeruginosa: fur mutants produce elevated alginate levels

J Bacteriol. 1997 Mar;179(5):1452-9. doi: 10.1128/jb.179.5.1452-1459.1997.


The activities of fumarase- and manganese-cofactored superoxide dismutase (SOD), encoded by the fumC and sodA genes in Pseudomonas aeruginosa, are elevated in mucoid, alginate-producing bacteria and in response to iron deprivation (D. J. Hassett, M. L. Howell, P. A. Sokol, M. L. Vasil, and G. E. Dean, J. Bacteriol. 179:1442-1451, 1997). In this study, a 393-bp open reading frame, fagA (Fur-associated gene), was identified immediately upstream of fumC, in an operon with orfX and sodA. Two iron boxes or Fur (ferric uptake regulatory protein) binding sites were discovered just upstream of fagA. Purified P. aeruginosa Fur caused a gel mobility shift of a PCR product containing these iron box regions. DNA footprinting analysis revealed a 37-bp region that included the Fur binding sites and was protected by Fur. Primer extension analysis and RNase protection assays revealed that the operon is composed of at least three major iron-regulated transcripts. Four mucoid fur mutants produced 1.7- to 2.6-fold-greater fumarase activity and 1.7- to 2.3-greater amounts of alginate than wild-type organisms. A strain devoid of the alternative sigma factor AlgT(U) produced elevated levels of one major transcript and fumarase C and manganase-cofactored SOD activity, suggesting that AlgT(U) may either play a role in regulating this transcript or function in some facet of iron metabolism. These data suggest that the P. aeruginosa fagA, fumC, orfX, and sodA genes reside together on a small operon that is regulated by Fur and is transcribed in response to iron limitation in mucoid, alginate-producing bacteria.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Alginates / metabolism*
  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Binding Sites
  • DNA Footprinting
  • Fumarate Hydratase / genetics*
  • Fumarate Hydratase / metabolism
  • Gene Expression Regulation, Bacterial
  • Iron / metabolism*
  • Molecular Sequence Data
  • Mutagenesis
  • Open Reading Frames
  • Operon*
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / metabolism
  • Regulatory Sequences, Nucleic Acid
  • Repressor Proteins / genetics*
  • Repressor Proteins / metabolism
  • Sigma Factor / genetics
  • Sigma Factor / metabolism
  • Superoxide Dismutase / genetics*
  • Superoxide Dismutase / metabolism


  • AlgU protein, Pseudomonas aeruginosa
  • Alginates
  • Bacterial Proteins
  • FagA protein, Pseudomonas aeruginosa
  • Repressor Proteins
  • Sigma Factor
  • ferric uptake regulating proteins, bacterial
  • Iron
  • SodA protein, Bacteria
  • Superoxide Dismutase
  • fumarase C
  • Fumarate Hydratase

Associated data

  • GENBANK/U59458