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.
S
Form Part of a Cascade That Controls Alginate Production in
Azotobacter vinelandii
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
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
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.
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