title: Heme rescues a two-component system Leptospira biflexa mutant.
abstract: BACKGROUND
  Heme is typically a major iron source for bacteria, but little is known about how bacteria of the Leptospira genus, composed of both saprophytic and pathogenic species, access heme.
  
  
  RESULTS
  In this study, we analysed a two-component system of the saprophyte Leptospira biflexa. In vitro phosphorylation and site-directed mutagenesis assays showed that Hklep is a histidine kinase which, after autophosphorylation of a conserved histidine, transfers the phosphate to an essential aspartate of the response regulator Rrlep. Hklep/Rrlep two-component system mutants were generated in L. biflexa. The mutants could only grow in medium supplemented with hemin or delta-aminolevulinic acid (ALA). In the pathogen L. interrogans, the hklep and rrlep orthologous genes are located between hemE and hemL genes, which encode proteins involved in heme biosynthesis. The L. biflexa hklep mutant could be complemented with a replicative plasmid harbouring the L. interrogans orthologous gene, suggesting that these two-component systems are functionally similar. By real-time quantitative reverse transcription-PCR, we also observed that this two-component system might influence the expression of heme biosynthetic genes.
  
  
  CONCLUSIONS
  These findings demonstrate that the Hklep/Rrlep regulatory system is critical for the in vitro growth of L. biflexa, and suggest that this two-component system is involved in a complex mechanism that regulates the heme biosynthetic pathway.
authors.affiliation: Unité de Biologie des Spirochètes, Institut Pasteur, Paris, France. hlouvel@pasteur.fr
authors.forename: Hélène
authors.initials: H
authors.lastname: Louvel
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Betton
authors.forename: Mathieu
authors.initials: M
authors.lastname: Picardeau
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D006418:Heme / Q000494:pharmacology*; D006427:Hemin / Q000494:pharmacology; D007919:Leptospira / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D001426:Bacterial Proteins; D006418:Heme; D006427:Hemin