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Applied and Environmental Microbiology, April 2000, p. 1460-1467, Vol. 66, No. 4
Department of Biology, Utah State University,
Logan, Utah 84322-5305
Received 24 September 1999/Accepted 20 January 2000
To investigate the role of superoxide dismutases (SOD) in root
colonization and oxidative stress, mutants of Pseudomonas
putida lacking manganese-superoxide dismutase (MnSOD)
(sodA), iron-superoxide dismutase (FeSOD)
(sodB), or both were generated. The sodA sodB mutant did not grow on components washed from bean root surfaces or
glucose in minimal medium. The sodB and sodA
sodB mutants were more sensitive than wild type to oxidative
stress generated within the cell by paraquat treatment. In single
inoculation of SOD mutants on bean, only the sodA sodB
double mutant was impaired in growth on root surfaces. In mixed
inoculations with wild type, populations of the sodA mutant
were equal to those of the wild type, but levels of the
sodB mutant and, to a great extent, the sodA
sodB mutant, were reduced. Confocal microscopy of young bean
roots inoculated with green fluorescent protein-tagged cells showed
that wild type and SOD single mutants colonized well predominantly at
the root tip but that the sodA sodB double mutant grew
poorly at the tip. Our results indicate that FeSOD in P. putida is more important than MnSOD in aerobic metabolism and
oxidative stress. Inhibition of key metabolic enzymes by increased
levels of superoxide anion may cause the impaired growth of SOD mutants
in vitro and in planta.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Superoxide Dismutase Activity in Pseudomonas
putida Affects Utilization of Sugars and Growth on Root
Surfaces
*
Corresponding author. Mailing address: Department of
Biology, Utah State University, Logan, UT 84322-5305. Phone: (435)
797-3407. Fax: (435) 797-1575. E-mail:
anderson{at}biology.usu.edu.
Journal paper number 7163 of the Utah Agricultural Experiment Station.
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