Journal of Bacteriology, December 1999, p. 7176-7184, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
22) Controls Alginate
Production and Tolerance to Environmental Stress in
Pseudomonas syringae
Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, Oklahoma 74078
Received 20 July 1999/Accepted 17 September 1999
Pseudomonas aeruginosa and the phytopathogen P. syringae produce the exopolysaccharide alginate, which is a
copolymer of D-mannuronic and L-guluronic
acids. One of the key regulatory genes controlling alginate
biosynthesis in P. aeruginosa is algT, which
encodes the alternate sigma factor,
22. In the present
study, the algT gene product from P. syringae pv. syringae showed 90% amino acid identity with its P. aeruginosa counterpart, and sequence analysis of the
region flanking algT in P. syringae revealed
the presence of nadB, mucA, and
mucB in an arrangement virtually identical to that of
P. aeruginosa. An algT mutant of P. syringae was defective in alginate production but could be
complemented with wild-type algT from P. syringae or P. aeruginosa when expressed in
trans. The algT mutant also displayed increased
sensitivity to heat, paraquat, and hydrogen peroxide
(H2O2); the latter two compounds are known to
generate reactive oxygen intermediates. Signals for activation
of algT gene expression in P. syringae were
investigated with an algT::uidA transcriptional fusion. Like that in P. aeruginosa,
algT transcription in P. syringae was activated
by heat shock. However, algT expression in P. syringae was also stimulated by osmotic stress and by exposure to
paraquat, H2O2, and copper sulfate. The latter
two compounds are frequently encountered during colonization of plant
tissue and may be unique signals for algT activation in
P. syringae.
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