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Journal of Bacteriology, December 2001, p. 6787-6793, Vol. 183, No. 23
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.23.6787-6793.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

The Global Regulators GacA and sigma S Form Part of a Cascade That Controls Alginate Production in Azotobacter vinelandii

Miguel Castañeda, Judith Sánchez, Soledad Moreno, Cinthia Núñez, and Guadalupe Espín*

Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca Morelos 62250, Mexico

Received 26 June 2001/Accepted 12 September 2001

Transcription of the Azotobacter vinelandii algD gene, which encodes GDP-mannose dehydrogenase (the rate-limiting enzyme of alginate synthesis), starts from three sites: p1, p2, and p3. The sensor kinase GacS, a member of the two-component regulatory system, is required for transcription of algD from its three sites during the stationary phase. Here we show that algD is expressed constitutively throughout the growth cycle from the p2 and p3 sites and that transcription from p1 started at the transition between the exponential growth phase and stationary phase. We constructed A. vinelandii strains that carried mutations in gacA encoding the cognate response regulator of GacS and in rpoS coding for the stationary-phase sigma S factor. The gacA mutation impaired alginate production and transcription of algD from its three promoters. Transcription of rpoS was also abolished by the gacA mutation. The rpoS mutation impaired transcription of algD from the p1 promoter and increased it from the p2 sigma E promoter. The results of this study provide evidence for the predominant role of GacA in a regulatory cascade controlling alginate production and gene expression during the stationary phase in A. vinelandii.

* Corresponding author. Mailing address: Departamento de Microbiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apdo. Postal 510-3, Cuernavaca Morelos 62250, Mexico. Phone: 52-73-291644. Fax: 52-73-172388. E-mail: espin{at}ibt.unam.mx.

Journal of Bacteriology, December 2001, p. 6787-6793, Vol. 183, No. 23
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.23.6787-6793.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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