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Journal of Bacteriology, January 1999, p. 141-148, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

The Azotobacter vinelandii Response Regulator AlgR Is Essential for Cyst Formation

Cinthia Núñez, Soledad Moreno, Gloria Soberón-Chávez, and Guadalupe Espín*

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

Received 20 July 1998/Accepted 28 October 1998

Azotobacter vinelandii produces the exopolysaccharide alginate, which is essential for the encystment process. In Pseudomonas aeruginosa, as well as in A. vinelandii, the sigma E factor encoded by algU is required for transcription of algD, which encodes a key enzyme of the alginate biosynthetic pathway. The P. aeruginosa response regulator AlgR activates transcription of algD. fimS, located upstream algR, is proposed to encode the AlgR cognate sensor kinase. We have cloned and characterized the A. vinelandii algR gene; the deduced amino acid sequence of the protein encoded by this gene shows 79% identity with its P. aeruginosa homolog. Sequence analysis around the algR gene revealed the absence of a fimS homolog. Inactivation of A. vinelandii algR diminished alginate production by 50%, but did not affect algD transcription, and completely impaired the capacity to form mature cysts. Electron microscopy of the cyst structures formed by the algR mutant revealed that the encystment process is blocked at the step of exine formation. The transcriptional regulation of the A. vinelandii algR gene and the role of AlgR in alginate production differ significantly from those of its P. aeruginosa counterparts. These differences could be due to the fact that in A. vinelandii, alginate plays a role in encystment, a function not found in P. aeruginosa.

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

Journal of Bacteriology, January 1999, p. 141-148, Vol. 181, No. 1
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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