Osmoprotection mechanisms in rhizobia isolated from Vicia faba var. major and Cicer arietinum

Issue		Agron. Sustain. Dev. Volume 21, Number 6-7, September-November 2001 Symbiotic nitrogen fixation for Mediterranean areas


Page(s)		583 - 590
DOI		10.1051/agro:2001148

DOI: 10.1051/agro:2001148

Agronomie 21 (2001) 583-590

Osmoprotection mechanisms in rhizobia isolated from Vicia faba var. major and Cicer arietinum

Fatiha Brhada^a, M.C. Poggi^b, G. Van de Sype^b and Daniel Le Rudulier^b

^a Laboratoire de Microbiologie et Biologie moléculaire, Faculté des Sciences, Université Mohammed V, BP 1014, Rabat, Morocco
^b Laboratoire de Biologie Végétale et Microbiologie, Faculté des Sciences et Techniques, Université de Nice-Sophia Antipolis, France

(Received 22 January 2001; revised 9 May 2001; accepted 13 July 2001)

Abstract
Research of mechanisms involved in osmoprotection of two rhizobia strains isolated from nodules of Vicia faba var. major and one strain nodulating Cicer arietinum, showed that choline and glycine-betaine improved growth in salt stress conditions. Provided radioactive choline was converted into glycine betaine catabolized at low osmolarity and accumulated under osmotic stress. Enzyme activities involved in the synthesis of glycine betaine from choline were not modified by salt whereas addition of choline to the growth medium enhanced them. Exogenous radioactive glycine betaine was accumulated in salt stressed bacteria after one hour incubation but catabolized four hours later, suggesting a transient accumulation. Growth experiments indicated that betaine and its derivatives could be used as nitrogen and carbon sources. An investigation, by liquid phase chromatography, revealated accumulation of glutamate and alanine at different levels according to the strain and degree of stress.

Résumé
Mécanismes d'osmoprotection chez les rhizobia isolés de Vicia faba var. major et de Cicer arietinum. La recherche des mécanismes impliqués dans l'osmoprotection chez deux souches de rhizobium isolées des nodosités de Vicia faba var. major et une souche nodulant Cicer arietinum, a montré que la glycine bétaïne et la choline améliorent la croissance bactérienne sous stress salin. Lors d'études métaboliques, la choline intracellulaire radioactive est transformée en glycine bétaïne et ce indépendamment de l'osmolarité du milieu. En effet, les activités choline déshydrogénase et glycine bétaïne aldéhyde déshydrogénase ne sont pas modifiées par le sel. Néanmoins, la présence de la choline dans le milieu augmente les deux activités enzymatiques. L'incubation en présence de la glycine bétaïne durant une heure est suivie d'une accumulation de ce composé chez les cellules cultivées à 0,15 M NaCl. Cette accumulation n'a plus lieu quatre heures plus tard. Des expériences de croissance avec la glycine bétaïne ou ses métabolites montrent son utilisation comme source de carbone et d'azote. La recherche, par chromatographie en phase liquide a révélé l'accumulation du glutamate et de l'alanine à des niveaux variables en fonction de la souche et du degré de stress.

Key words: rhizobia / osmoprotection / choline / glycine betaine

Mots clés : rhizobia / choline / glycine betaine / osmoprotection

Correspondence and reprints: Fatiha Brhada
e-mail: fatibrhada@hotmail.com

Communicated by Jean-Jacques Drevon (Montpellier, France)

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