title: Enhanced oxygen consumption in Herbaspirillum seropedicae fnr mutants leads to increased NifA mediated transcriptional activation.
abstract: BACKGROUND
  Orthologous proteins of the Crp/Fnr family have been previously implicated in controlling expression and/or activity of the NifA transcriptional activator in some diazotrophs. This study aimed to address the role of three Fnr-like proteins from H. seropedicae SmR1 in controlling NifA activity and consequent NifA-mediated transcription activation.
  
  
  RESULTS
  The activity of NifA-dependent transcriptional fusions (nifA::lacZ and nifB::lacZ) was analysed in a series of H. seropedicae fnr deletion mutant backgrounds. We found that combined deletions in both the fnr1 and fnr3 genes lead to higher expression of both the nifA and nifB genes and also an increased level of nifH transcripts. Expression profiles of nifB under different oxygen concentrations, together with oxygen consumption measurements suggest that the triple fnr mutant has higher respiratory activity when compared to the wild type, which we believe to be responsible for greater stability of the oxygen sensitive NifA protein. This conclusion was further substantiated by measuring the levels of NifA protein and its activity in fnr deletion strains in comparison with the wild-type.
  
  
  CONCLUSIONS
  Fnr proteins are indirectly involved in controlling the activity of NifA in H. seropedicae, probably as a consequence of their influence on respiratory activity in relation to oxygen availability. Additionally we can suggest that there is some redundancy in the physiological function of the three Fnr paralogs in this organism, since altered respiration and effects on NifA activity are only observed in deletion strains lacking both fnr1 and fnr3.
authors.affiliation: Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, P.O. Box 19046, Curitiba, PR, 81531-990, Brazil. marcelo.buenobatista@gmail.com.
authors.forename: Marcelo Bueno
authors.initials: MB
authors.lastname: Batista
authors.affiliation: Department of Genetics, Universidade Federal do Paraná, P.O. Box 19071, Curitiba, PR, 81531-990, Brazil. wassem@ufpr.br.
authors.forename: Roseli
authors.initials: R
authors.lastname: Wassem
authors.affiliation: Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, P.O. Box 19046, Curitiba, PR, 81531-990, Brazil. fpedrosa@ufpr.br.
authors.forename: Fábio de Oliveira
authors.initials: Fde O
authors.lastname: Pedrosa
authors.affiliation: Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, P.O. Box 19046, Curitiba, PR, 81531-990, Brazil. souzaem@ufpr.br.
authors.forename: Emanuel Maltempi
authors.initials: EM
authors.lastname: de Souza
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Colney Lane, Norwich, NR4 7UH, UK. ray.dixon@jic.ac.uk.
authors.forename: Ray
authors.initials: R
authors.lastname: Dixon
authors.affiliation: Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, P.O. Box 19046, Curitiba, PR, 81531-990, Brazil. roseadele@ufpr.br.
authors.forename: Rose Adele
authors.initials: RA
authors.lastname: Monteiro
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D042803:Herbaspirillum / Q000235:genetics* / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000172:deficiency; D010100:Oxygen / Q000378:metabolism*; D014157:Transcription Factors / Q000172:deficiency* / Q000378:metabolism; D015533:Transcriptional Activation
chemical_list: D001426:Bacterial Proteins; D007506:Iron-Sulfur Proteins; C061338:NifA protein, Bacteria; D014157:Transcription Factors; D010100:Oxygen