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.
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
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.
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