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Role of glutathione in the growth of Bradyrhizobium sp. (peanut microsymbiont) under different environmental stresses and in symbiosis with the host plant

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Abstract:

Glutathione (GSH) plays an important role in the defence of microorganisms and plants against different environmental stresses. To determine the role of GSH under different stresses, such as acid pH, saline shock, and oxidative shock, a GSH-deficient mutant (Bradyrhizobium sp. 6144-S7Z) was obtained by disruption of the gshA gene, which encodes the enzyme -glutamylcysteine synthetase. Growth of the mutant strain was significantly reduced in liquid minimal saline medium, and the GSH content was very low, about 4% of the wild-type level. The defect, caused by disruption of the gshA gene in the growth of mutant strain, cannot be reversed by the addition of GSH (up to 100 µmol/L) to the liquid minimal saline medium, and the endogenous GSH level was approximately the same as that observed without the addition of GSH. In contrast, the wild-type strain increased the GSH content under these conditions. However, the growth of the mutant strain in a rich medium (yeast extract – mannitol) increased, suggesting that at least some but not all of the functions of GSH could be provided by peptides and (or) amino acids. The symbiotic properties of the mutant were similar to those found in the wild-type strain, indicating that the mutation does not affect the ability of the mutant to form effective nodules.Key words: glutathione, -glutamylcysteine synthetase, Bradyrhizobium sp., peanut.

Le glutathion (GSH) joue un rôle important dans la défense des micro-organismes et des plantes contre divers stress environnementaux. Afin de déterminer le rôle du GSH suite à différents stress comme un pH acide, choc salin et choc oxydatif, un mutant déficient en GSH (Bradyrhizobium sp. 6144-S7Z) fut obtenu en détruisant le gène gshA, qui code l'enzyme -glutamylcystéine synthétase. La croissance de la souche mutante était significativement diminuée en milieu salin minimal liquide et le contenu en GSH était très bas, environ 4 % du niveau du type sauvage. Le défaut causé par la destruction du gène gshA dans la croissance de la souche mutant n'a pu être renversé par l'ajout de jusqu'à 100 µmol/L de GSH dans le milieu salin minimal liquide et le niveau endogène de GSH était environ le même que celui observé sans ajout de GSH. En revanche, la souche sauvage a augmenté son contenu en GSH dans ces conditions. Toutefois, la croissance de la souche mutante en milieu riche (extrait de levure – mannitol) était supérieure ce qui indique qu'au moins certaines fonctions du GSH seraient fournies par des peptides et (ou) des acides aminés mais pas toutes. La propriété symbiotiques du mutant étaient semblables à celles retrouvées chez la souche sauvage ce qui indique que la mutation n'affecte pas la capacité du mutant à former des nodules efficaces.Mots clés : glutathion, -glutamylcystéine synthétase, Bradyrhizobium sp., arachide.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2006-07-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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