Fnr (EtrA) acts as a fine-tuning regulator of anaerobic metabolism in Shewanella oneidensis MR-1

Claribel Cruz-García, Alison E. Murray, Jorge L.M. Rodrigues, Jeffrey A. Gralnick, Lee Ann McCue, Margaret F. Romine, Frank E. Löffler, James M. Tiedje

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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. Conclusion: 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.

Original languageEnglish (US)
Article number64
JournalBMC microbiology
StatePublished - 2011

Bibliographical note

Funding Information:
We thank Xiaoyun Qiu for advice on the DNA microarray work, Valley Stewart and Joel Klappenbach for advice and discussion. We thank Benjamin K. Amos, Jed Costanza, Qingzhong Wu and Sara H. Thomas for technical assistance in the phenotypic characterization of the EtrA7-1 strain. We also acknowledge members of the Shewanella Federation for helpful discussions. This study was supported by Department of Energy grants DE-FG02-02ER63342 from the Genomics Program, Office of Biological and Environmental Research (awarded to JMT), DE-FG02-04ER63718.25 from the Environmental Remediation Science Division, Biological and Environmental Research (awarded to FEL) and DE-FG02-04ER63942 from the Genomes to Life Program, Office of Biological and Environmental Research (awarded to LAM). Contributions by MFR and LAM were performed at Pacific Northwest National Laboratory, which is operated by Battelle for the United States Department of Energy under Contract DE-AC05-76RL01830.


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