title: Fnr (EtrA) acts as a fine-tuning regulator of anaerobic metabolism in Shewanella oneidensis MR-1.
abstract: BACKGROUND
  EtrA in Shewanella oneidensis MR-1, a model organism for study of adaptation to varied redox niches, shares 73.6% and 50.8% amino acid sequence identity with the oxygen-sensing regulators Fnr in E. coli and Anr in Pseudomonas aeruginosa, respectively; however, its regulatory role of anaerobic metabolism in Shewanella spp. is complex and not well understood.
  
  
  RESULTS
  The expression of the nap genes, nrfA, cymA and hcp was significantly reduced in etrA deletion mutant EtrA7-1; however, limited anaerobic growth and nitrate reduction occurred, suggesting that multiple regulators control nitrate reduction in this strain. Dimethyl sulfoxide (DMSO) and fumarate reductase gene expression was down-regulated at least 2-fold in the mutant, which, showed lower or no reduction of these electron acceptors when compared to the wild type, suggesting both respiratory pathways are under EtrA control. Transcript analysis further suggested a role of EtrA in prophage activation and down-regulation of genes implicated in aerobic metabolism.
  
  
  CONCLUSIONS
  In contrast to previous studies that attributed a minor regulatory role to EtrA in Shewanella spp., this study demonstrates that EtrA acts as a global transcriptional regulator and, in conjunction with other regulators, fine-tunes the expression of genes involved in anaerobic metabolism in S. oneidensis strain MR-1. Transcriptomic and sequence analyses of the genes differentially expressed showed that those mostly affected by the mutation belonged to the "Energy metabolism" category, while stress-related genes were indirectly regulated in the mutant possibly as a result of a secondary perturbation (e.g. oxidative stress, starvation). We also conclude based on sequence, physiological and expression analyses that this regulator is more appropriately termed Fnr and recommend this descriptor be used in future publications.
authors: Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824-1325, USA. tiedjej@msu.edu
authors: Claribel
authors: C
authors: Cruz-García
authors: Alison E
authors: AE
authors: Murray
authors: Jorge L M
authors: JL
authors: Rodrigues
authors: Jeffrey A
authors: JA
authors: Gralnick
authors: Lee Ann
authors: LA
authors: McCue
authors: Margaret F
authors: MF
authors: Romine
authors: Frank E
authors: FE
authors: Löffler
authors: James M
authors: JM
authors: Tiedje
mesh_terms: D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004734:Energy Metabolism; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D053858:Metabolic Networks and Pathways / Q000235:genetics*; D009566:Nitrates / Q000378:metabolism; D017422:Sequence Analysis, DNA; D020592:Shewanella / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; C433797:EtrA protein, Shewanella; D009566:Nitrates; D014157:Transcription Factors