Aerobic growth deficient Haemophilus influenzae mutants are non-virulent: implications on metabolism

Int J Med Microbiol. 2003 Jun;293(2-3):145-52. doi: 10.1078/1438-4221-00261.


We investigated aerobic metabolism in Haemophilus influenzae to better understand its essential physiological growth pathways. We describe the isolation and characterization of transposon insertions leading to knockout mutations in lpdA, encoding dihydrolipoamide dehydrogenase. H. influenzae Rd lpdA::Tn10d-cat mutants were unable to grow aerobically and an H. influenzae type b lpdA::Tn10d-cat mutant was significantly attenuated in an infant rat infection model. Since LpdA is a functional subunit of both pyruvate dehydrogenase (aceEF) and alpha-ketoglutarate dehydrogenase (sucAB) the phenotype of the lpdA mutant was further explored by creating separate knockout mutants in the sucAB and aceEF loci. DeltaaceEF and deltasucAB mutants were both significantly attenuated in virulence in the infant rat, but only the sucAB mutant was able to grow aerobically. We therefore conclude that the ability for aerobic growth is critical for invasive disease, and furthermore that a TCA cycle enzyme, alpha-ketoglutarate dehydrogenase, appears to contribute a key metabolic function in vivo, but is not required for growth under laboratory conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aerobiosis
  • Animals
  • Citric Acid Cycle
  • DNA Transposable Elements
  • DNA, Bacterial
  • Gene Deletion
  • Haemophilus Infections / enzymology
  • Haemophilus Infections / microbiology*
  • Haemophilus influenzae / enzymology
  • Haemophilus influenzae / genetics
  • Haemophilus influenzae / growth & development*
  • Ketoglutarate Dehydrogenase Complex / deficiency
  • Ketoglutarate Dehydrogenase Complex / genetics
  • Mutagenesis, Insertional
  • Mutation
  • Pyruvate Dehydrogenase (Lipoamide) / deficiency
  • Pyruvate Dehydrogenase (Lipoamide) / genetics
  • Rats
  • Rats, Sprague-Dawley


  • DNA Transposable Elements
  • DNA, Bacterial
  • Pyruvate Dehydrogenase (Lipoamide)
  • Ketoglutarate Dehydrogenase Complex