Journal of Bacteriology, June 1999, p. 3478-3485, Vol. 181, No. 11
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbiology and Molecular Genetics1 and Department of Entomology and Plant Pathology,2 Oklahoma State University, Stillwater, Oklahoma 74078, and Department of Microbiology and Immunology, University of Illinois College of Medicine, Chicago, Illinois 606123
Received 5 January 1999/Accepted 24 March 1999
Both Pseudomonas aeruginosa and the phytopathogen
P. syringae produce the exopolysaccharide alginate.
However, the environmental signals that trigger alginate gene
expression in P. syringae are different from those in
P. aeruginosa with copper being a major signal in P. syringae. In P. aeruginosa, the alternate sigma
factor encoded by algT (
22) and the response
regulator AlgR1 are required for transcription of algD, a
gene which encodes a key enzyme in the alginate biosynthetic pathway.
In the present study, we cloned and characterized the gene encoding
AlgR1 from P. syringae. The deduced amino acid sequence of
AlgR1 from P. syringae showed 86% identity to its P. aeruginosa counterpart. Sequence analysis of the region flanking
algR1 in P. syringae revealed the presence of
argH, algZ, and hemC in an arrangement virtually identical to that reported in P. aeruginosa. An algR1 mutant, P. syringae
FF5.32, was defective in alginate production but could be complemented
when algR1 was expressed in trans. The
algD promoter region in P. syringae
(PsalgD) was also characterized and shown to diverge
significantly from the algD promoter in P. aeruginosa. Unlike P. aeruginosa, algR1
was not required for the transcription of algD in P. syringae, and PsalgD lacked the consensus sequence
recognized by AlgR1. However, both the algD and
algR1 upstream regions in P. syringae contained the consensus sequence recognized by
22, suggesting that
algT is required for transcription of both genes.
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