Identification of a nifA-like regulatory gene of Azospirillum brasilense Sp7 expressed under conditions of nitrogen fixation and in the presence of air and ammonia

Genetic complementation of a spontaneous mutant, impaired in flocculation, Congo red binding, and colonization of root surface, led to the identification of a new regulatory gene in Azospirillum brasilense Sp7, designated flcA. The deduced amino acid sequence of flcA shared high similarity with a family of transcriptional activators of the LuxR-UhpA family. The most significant match was with the AgmR protein, an activator for glycerol metabolism in Pseudomonas aeruginosa. Derivatives of Sp7 resulting from site-directed Tn5 mutagenesis in the flcA coding sequence were constructed by marker exchange. Characterization of the resulting mutant strains showed that flcA controls the production of capsular polysaccharides, the flocculation process in culture, and the colonization of the root surface of wheat. This study provides new information on the genetic control of the mechanism of plant root colonization by Azospirillum.

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TheAzospirillum brasilense rpoNgene is involved in nitrogen fixation, nitrate assimilation, ammonium uptake, and flagellar biosynthesis

Canadian Journal of Microbiology ◽

10.1139/m96-064 ◽

1996 ◽

Vol 42 (5) ◽

pp. 467-478 ◽

Cited By ~ 18

Author(s):

Anne Milcamps ◽

Anne Van Dommelen ◽

John Stigter ◽

Jos Vanderleyden ◽

Frans J. de Bruijn

Keyword(s):

Nitrogen Fixation ◽

Azospirillum Brasilense ◽

Nitrate Assimilation ◽

Ammonium Assimilation ◽

Gene Replacement ◽

Ammonium Uptake ◽

Significant Similarity ◽

Sigma 54 ◽

Azospirillum Brasilense Sp7

The rpoN (ntrA) gene (encoding sigma 54) of Azospirillum brasilense Sp7 was isolated by using conserved rpoN primers and the polymerase chain reaction, and its nucleotide sequence was determined. The deduced amino acid sequence of the RpoN protein was found to share a high degree of homology with other members of the sigma 54 family. Two additional open reading frames were found in the Azospirillum brasilense rpoN region, with significant similarity to equivalent regions surrounding the rpoN locus in other bacteria. An rpoN mutant of Azospirillum brasilense Sp7 was constructed by gene replacement and found to be defective in nitrogen fixation, nitrate assimilation, and ammonium uptake. Lack of ammonium uptake was also found in previously isolated Azospirillum brasilense ntrB and ntrC mutants, further supporting the role of the ntr system in this process. In addition, the rpoN mutant was found to be nonmotile, suggesting a role of RpoN in Azospirillum brasilense flagellar biosynthesis.Key words: Azospirillum brasilense, sigma factor, nitrogen fixation, ammonium assimilation, motility.

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Identification of DNA Regions Homologous to Nitrogen Fixation Genes nifE, nifUS and fixABC in Azospirillum brasilense Sp7

Microbiology ◽

10.1099/00221287-135-5-1047 ◽

1989 ◽

Vol 135 (5) ◽

pp. 1047-1059 ◽

Cited By ~ 2

Author(s):

M. Galimand ◽

B. Perroud ◽

F. Delorme ◽

A. Paquelin ◽

C. Vieille ◽

...

Keyword(s):

Nitrogen Fixation ◽

Azospirillum Brasilense ◽

Azospirillum Brasilense Sp7 ◽

Nitrogen Fixation Genes

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A mutant of Azospirillum brasilense Sp7 impaired in flocculation with a modified colonization pattern and superior nitrogen fixation in association with wheat.

Applied and Environmental Microbiology ◽

10.1128/aem.61.5.1987-1995.1995 ◽

1995 ◽

Vol 61 (5) ◽

pp. 1987-1995 ◽

Cited By ~ 57

Author(s):

S Katupitiya ◽

J Millet ◽

M Vesk ◽

L Viccars ◽

A Zeman ◽

...

Keyword(s):

Nitrogen Fixation ◽

Azospirillum Brasilense ◽

Colonization Pattern ◽

Azospirillum Brasilense Sp7

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Molybdenum incorporation in denitrifying Azospirillum brasilense Sp7

Canadian Journal of Microbiology ◽

10.1139/m92-171 ◽

1992 ◽

Vol 38 (10) ◽

pp. 1042-1047 ◽

Cited By ~ 2

Author(s):

Christian Chauret ◽

Wilfredo L. Barraquio ◽

Roger Knowles

Keyword(s):

Nitrate Reductase ◽

Key Words ◽

Nitrate Reduction ◽

Gel Electrophoresis ◽

Azospirillum Brasilense ◽

Paracoccus Denitrificans ◽

Free Medium ◽

Azospirillum Brasilense Sp7

Nondenaturating disc gel electrophoresis revealed that 99Mo was incorporated into the nitrate reductase of Azospirillum brasilense grown in the absence but not in the presence of tungstate. Under denitrifying conditions, A. brasilense grown in tungsten-free medium steadily accumulated 99Mo for 12 h. In contrast, Paracoccus denitrificans grown under the same conditions ceased uptake after 1 h. However, both bacteria were incapable of accumulating significant amounts of 99Mo in media containing 10 mM tungstate, even though nitrate was reduced by A. brasilense. Aerobically grown A. brasilense cells transported 99Mo more efficiently than anaerobically grown cells. Key words: Azospirillum brasilense, tungsten, molybdenum incorporation, nitrate reduction.

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