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Journal of Bacteriology, March 2000, p. 1748-1753, Vol. 182, No. 6
Instituto de Bioquímica y Biologia
Molecular, Facultad de Ciencias Exactas, Universidad Nacional de La
Plata, La Plata, Argentina1; MSU-DOE
Plant Research Laboratory and Department of Microbiology, Michigan
State University, East Lansing, MI 488242; and
Department of Molecular and Cell Biology, Institute of
Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25
2ZD, United Kingdom3
Received 20 September 1999/Accepted 20 December 1999
The isolation of rhizobial strains which exhibit an intrinsic
tolerance to acidic conditions has been reported and has facilitated studies on the basic mechanisms underlying acid tolerance.
Rhizobium tropici strain CIAT899 displays a high intrinsic
tolerance to acidity and therefore was used in this work to study the
molecular basis of bacterial responses to acid conditions and other
environmental stresses. We generated a collection of R. tropici CIAT899 mutants affected in acid tolerance using
Tn5-luxAB mutagenesis, and one mutant strain
(CIAT899-13T2), which fails to grow under acid conditions, was
characterized in detail. Strain CIAT899-13T2 was found to contain a
single Tn5-luxAB insertion in a gene showing a high degree
of similarity with the Escherichia coli gshB gene, encoding the enzyme glutathione synthetase. Intracellular potassium pools and
intracellular pH levels were found to be lower in the mutant than in
the parent. The glutathione-deficient mutant was shown to be sensitive
to weak organic acids, osmotic and oxidative stresses, and the presence
of methylglyoxal. Glutathione restores responses to these stresses
almost to wild-type levels. Our data show that in R. tropici the production of glutathione is essential for growth in
extreme environmental conditions. The mutant strain CIAT899-13T2 induced effective nodules; however, it was found to be outcompeted by
the wild-type strain in coinoculation experiments.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Glutathione Is Involved in Environmental Stress
Responses in Rhizobium tropici, Including Acid
Tolerance
*
Corresponding author. Mailing address: Instituto de
Bioquímica y Biologia Molecular, Facultad de Ciencias Exactas,
Universidad Nacional de La Plata, Calles 47 y 115 (1900), La
Plata, Argentina. Phone: 54 221 4250497, ext. 61. Fax: 54 221 4226947. E-mail: aguilar{at}nahuel.biol.unlp.edu.ar.
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