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J Bacteriol, February 1998, p. 871-880, Vol. 180, No. 4
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Identification of AlcR, an AraC-Type Regulator of Alcaligin Siderophore Synthesis in Bordetella bronchiseptica and Bordetella pertussis

Elizabeth Pradel,1 Nicole Guiso,2 and Camille Locht1,*

INSERM U447, Institut Pasteur de Lille, 59019 Lille Cedex,1 and Laboratoire des Bordetella, Institut Pasteur, 75724 Paris Cedex 15,2 France

Received 5 September 1997/Accepted 6 December 1997

A Fur titration assay was used to isolate DNA fragments bearing putative Fur binding sites (FBS) from a partial Bordetella bronchiseptica genomic DNA library. A recombinant plasmid bearing a 3.5-kb DNA insert was further studied. Successive deletions in the cloned fragment enabled us to map a putative FBS at about 2 kb from one end. Sequence analysis revealed the presence of an FBS upstream from a new gene encoding an AraC-type transcriptional regulator. The deduced protein displays similarity to PchR, an activator of pyochelin siderophore and ferripyochelin receptor synthesis in Pseudomonas aeruginosa. Homologous genes in Bordetella pertussis and Bordetella parapertussis were PCR amplified, and sequence comparisons indicated a very high conservation in the three species. The B. pertussis and B. bronchiseptica chromosomal genes were inactivated by allelic exchange. Under low-iron growth conditions, the mutants did not secrete the alcaligin siderophore and lacked AlcC, an alcaligin biosynthetic enzyme. Alcaligin production was restored after transformation with a plasmid bearing the wild-type gene. On the basis of its role in regulation of alcaligin biosynthesis, the new gene was designated alcR. Additional sequence determination showed that alcR is located about 2 kb downstream from the alcABC operon and is transcribed in the same orientation. Two tightly linked open reading frames, alcD and alcE, were identified between alcC and alcR. AlcE is a putative iron-sulfur protein; AlcD shows no homology with the proteins in the database. The production of major virulence factors and colonization in the mouse respiratory infection model are AlcR independent.

* Corresponding author. Mailing address: INSERM U447, Institut Pasteur de Lille, 1 rue du Prof. Calmette, BP 245, 59019 Lille Cedex, France. Phone: 33 (0) 3 20 87 11 51. Fax: 33 (0) 3 20 87 11 58. E-mail: Camille.Locht{at}pasteur-lille.fr.




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