Fnr (EtrA) acts as a fine-tuning regulator of anaerobic metabolism in Shewanella oneidensis MR-1
1 Center for Microbial Ecology, Michigan State University, East Lansing, Michigan 48824-1325, USA
2 Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan 48824-1325, USA
3 Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824-1325, USA
4 Department of Biology, University of Texas at Arlington, Arlington, Texas 76019, USA
5 Department of Microbiology, University of Minnesota, St. Paul, MN 55108, USA
6 Pacific Northwest National Laboratory, Richland, Washington 99352, USA
7 Department of Microbiology, University of Tennessee, Knoxville, MN 37996, USA
8 Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, MN 37996, USA
9 Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
10 Georgia Institute of Technology, School of Civil and Environmental Engineering, 311 Ferst Drive, Atlanta, GA 30332-0512, USA
11 Division of Earth and Ecosystem Sciences, Desert Research Institute, Reno, NV 89512, USA
BMC Microbiology 2011, 11:64 doi:10.1186/1471-2180-11-64Published: 30 March 2011
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.
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.
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.