Document Detail

Regulation of gene expression in response to oxygen in Rhizobium etli: role of FnrN in fixNOQP expression and in symbiotic nitrogen fixation.
MedLine Citation:
PMID:  11717256     Owner:  NLM     Status:  MEDLINE    
Previously, we reported finding duplicated fixNOQP operons in Rhizobium etli CFN42. One of these duplicated operons is located in the symbiotic plasmid (fixNOQPd), while the other is located in a cryptic plasmid (fixNOQPf). Although a novel FixL-FixKf regulatory cascade participates in microaerobic expression of both fixNOQP duplicated operons, we found that a mutation in fixL eliminates fixNOQPf expression but has only a moderate effect on expression of fixNOQPd. This suggests that there are differential regulatory controls. Interestingly, only the fixNOQPd operon was essential for symbiotic nitrogen fixation (L. Girard, S. Brom, A. Dávalos, O. Lopez, M. Soberón, and D. Romero, Mol. Plant-Microbe Interact. 13:1283-1292, 2000). Searching for potential candidates responsible for the differential expression, we characterized two fnrN homologs (encoding transcriptional activators of the cyclic AMP receptor protein [CRP]-Fnr family) in R. etli CFN42. One of these genes (fnrNd) is located on the symbiotic plasmid, while the other (fnrNchr) is located on the chromosome. Analysis of the expression of the fnrN genes using transcriptional fusions with lacZ showed that the two fnrN genes are differentially regulated, since only fnrNd is expressed in microaerobic cultures of the wild-type strain while fnrNchr is negatively controlled by FixL. Mutagenesis of the two fnrN genes showed that both genes participate, in conjunction with FixL-FixKf, in the microaerobic induction of the fixNOQPd operon. Participation of these genes is also seen during the symbiotic process, in which mutations in fnrNd and fnrNchr, either singly or in combination, lead to reductions in nitrogen fixation. Therefore, R. etli employs a regulatory circuit for induction of the fixNOQPd operon that involves at least three transcriptional regulators of the CRP-Fnr family. This regulatory circuit may be important for ensuring optimal production of the cbb(3), terminal oxidase during symbiosis.
O Lopez; C Morera; J Miranda-Rios; L Girard; D Romero; M Soberón
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of bacteriology     Volume:  183     ISSN:  0021-9193     ISO Abbreviation:  J. Bacteriol.     Publication Date:  2001 Dec 
Date Detail:
Created Date:  2001-11-21     Completed Date:  2001-12-26     Revised Date:  2010-09-14    
Medline Journal Info:
Nlm Unique ID:  2985120R     Medline TA:  J Bacteriol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  6999-7006     Citation Subset:  IM    
Departamento de Microbiología Molecular, Instituto de Biotecnología, UNAM, Cuernavaca, Morelos, 62250, Mexico.
Data Bank Information
Bank Name/Acc. No.:
GENBANK/AF083916;  AF083917
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MeSH Terms
Amino Acid Sequence
Bacterial Proteins / biosynthesis*,  metabolism*
Cytochrome c Group / biosynthesis*
Gene Duplication
Gene Expression Regulation, Bacterial
Genes, Bacterial
Genes, Regulator
Hemeproteins / metabolism
Membrane Proteins / biosynthesis
Models, Genetic
Molecular Sequence Data
Nitrogen Fixation / genetics*
Nitrogenase / genetics,  metabolism
Oxygen / pharmacology*
Phaseolus / microbiology
Rhizobium / drug effects,  genetics*
Sequence Homology, Amino Acid
Symbiosis / genetics
Transcription Factors*
Reg. No./Substance:
0/Bacterial Proteins; 0/Cytochrome c Group; 0/FixL protein, Bacteria; 0/FixN protein, bacteria; 0/FixQ protein, Bacteria; 0/FnrN protein, Rhizobium leguminosarum; 0/Hemeproteins; 0/Membrane Proteins; 0/Transcription Factors; 0/cytochrome FixO; 0/cytochrome FixP; 131201-22-4/FixK protein, Bacteria; 7782-44-7/Oxygen; EC

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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