Titre
Indole-3-acetic acid (IAA) synthesis in the biocontrol strain CHA0 of Pseudomonas fluorescens: role of tryptophan side chain oxidase.
Type
article
Institution
Externe
Périodique
Journal of General Microbiology
Auteur(s)
Oberhänsli, T.
Auteure/Auteur
Défago, G.
Auteure/Auteur
Haas, D.
Auteure/Auteur
Liens vers les personnes
ISSN
0022-1287
Statut éditorial
Publié
Date de publication
1991
Volume
137
Numéro
10
Première page
2273
Dernière page/numéro d’article
2279
Langue
anglais
Résumé
Pseudomonas fluorescens strain CHA0 is an effective biocontrol agent against soil-borne fungal plant pathogens. In this study, indole-3-acetic acid (IAA) biosynthesis in strain CHA0 was investigated. Two key enzyme activities were found to be involved: tryptophan side chain oxidase (TSO) and tryptophan transaminase. TSO was induced in the stationary growth phase. By fractionation of a cell extract of strain CHA0 on DEAE-Sepharose, two distinct peaks of constitutive tryptophan transaminase activity were detected. A pathway leading from tryptophan to IAA via indole-3-acetamide, which occurs in Pseudomonas syringae subsp. savastanoi, was not present in strain CHA0. IAA synthesis accounted for less than or equal to 1.5% of exogenous tryptophan consumed by resting cells of strain CHA0, indicating that the bulk of tryptophan was catabolized via yet another pathway involving anthranilic acid as an intermediate. Strain CHA750, a mutant lacking TSO activity, was obtained after Tn5 mutagenesis of strain CHA0. In liquid cultures (pH 6.8) supplemented with 10 mM-L-tryptophan, growing cells of strains CHA0 and CHA750 synthesized the same amount of IAA, presumably using the tryptophan transaminase pathway. In contrast, resting cells of strain CHA750 produced five times less IAA in a buffer (pH 6.0) containing 1 mM-L-tryptophan than did resting cells of the wild-type, illustrating the major contribution of TSO to IAA synthesis under these conditions. In artificial soils at pH approximately 7 or pH approximately 6, both strains had similar abilities to suppress take-all disease of wheat or black root rot of tobacco. This suggests that TSO-dependent IAA synthesis is not essential for disease suppression.
Sujets
PID Serval
serval:BIB_B3A63B02C4D8
PMID
Date de création
2008-01-25T16:01:07.295Z
Date de création dans IRIS
2025-05-21T02:19:06Z