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Appl. Environ. Microbiol., Jun 1995, 2172-2179, Vol 61, No. 6
SP Kidambi, GW Sundin, DA Palmer, AM Chakrabarty and CL Bender
Plant-associated pseudomonads are commonly exposed to copper bactericides,
which are applied to reduce the disease incidence caused by these bacteria.
Consequently, many of these bacteria have acquired resistance or tolerance
to copper salts. We recently conducted a survey of 37 copper-resistant
(Cur) Pseudomonas spp., including P. cepacia, P. fluorescens, P. syringae,
and P. viridiflava, and found that a subset of the P. syringae strains
showed a dramatic increase in exopolysaccharide (EPS) production on
mannitol-glutamate medium containing CuSO4 at 250 micrograms/ml. A modified
carbazole assay indicated that the EPS produced on copper-amended media
contained high levels of uronic acids, suggesting that the EPS was
primarily alginic acid. Uronic acids extracted from selected strains were
further confirmed to be alginate by demonstrating their sensitivity to
alginate lyase and by descending paper chromatography following acid
hydrolysis. Subinhibitory levels of arsenate, cobalt, lithium, rubidium,
molybdenum, and mercury did not induce EPS production, indicating that
alginate biosynthesis is not induced in P. syringae cells exposed to these
heavy metals. A 200-kb plasmid designated pPSR12 conferred a stably mucoid
phenotype to several P. syringae recipients and also increased their
resistance to cobalt and arsenate. A cosmid clone constructed from pPSR12
which conferred a stably mucoid phenotype to several P. syringae strains
but not to Pseudomonas aeruginosa was obtained. Results obtained in this
study indicate that some of the signals and regulatory genes for alginate
production in P. syringae differ from those described for alginate
production in P. aeruginosa.
Copyright © 1995, American Society for Microbiology
Copper as a signal for alginate synthesis in Pseudomonas syringae pv. syringae
Department of Plant Pathology, Oklahoma State University, Stillwater 74078-9947, USA.
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