Rhizobium leguminosarum bv. viciae produces a novel cyclic trihydroxamate siderophore, vicibactin

Abstract

Trihydroxamate siderophores were isolated from iron-def icient cultures of three strains of Rhilobiurn legurninorarum biovar wiciae, two from Japan (WSM709, WSM710) and one from the Mediterranean (WU235), and from a Tn5-induced mutant of WSM710 (MNF7101). The first three all produced the same compound (vicibactin), which was uncharged and could be purified by solvent extraction into benzyl alcohol. The gallium and ferric complexes of vicibactin were extractable into benzyl alcohol at pH 59, while metal-free vicibactin could be extracted with good yield at pH 89. The trihydroxamate from MNF7101 (vicibactin 7101) could not be extracted into benzyl alcohol, but its cationic nature permitted purification by chromatography on Sephadex CM-25 (NHt form). Relative molecular masses and empirical formulae were obtained from fast-atom-bombardment MS. The structures were derived from one-and two-dimensional IH and I3C NMR spectroscopy, using DQF-COSY, NOESY, HMQC and HMBC techniques on the compounds dissolved in methanol-d, and DMSOd6. Vicibactin proves to be a cyclic molecule containing three residues each of (R)-2,5-diamino-N2-acetyl-N5-hydroxypentanoic acid (W-acetyl-M-hydroxy-Dornithine) and (R)-3-hydroxybutanoic acid, arranged alternately, with alternating ester and peptide bonds. Vicibactin 7101 differed only in lacking the acetyl substitution on the N2 of the W-hydroxyornithine, resulting in net positive charge; it was still functional as a siderophore and promoted 55Fe uptake by iron-starved cells of WSM710 in the presence of an excess of phosphate. The rate of vicibactin biosynthesis by iron-def icient cells of WSM710 was essentially constant between pH 5.5 and 79, but much decreased at pH 59. When iron-starved cultures were supplemented with potential precursors for vicibactin, the rates of i t s synthesis were consistent with both fi hydroxybutyrate and ornithine being precursors. At least three genes seem likely to be involved in synthesis of vicibactin from ornithine and fi hydroxybutyrate : a hydroxylase adding the -OH group to the N5 of ornithine, an acetylase adding the acetyl group to the N2 of ornithine, and a peptide synthetase system.

Characterization and Fungal Inhibition Activity of Siderophore from Wheat Rhizosphere Associated Acinetobacter calcoaceticus Strain HIRFA32

“…The siderophores produced by rhizosphere bacteria can supply iron to plants under iron limiting conditions [9] many strains of rhizobacteria, which are effective in biocontrol, produce siderophore. Siderophore also can act as one of the factors for inducing systemic resistance of plants and preventing growth of certain pathogenic bacteria and fungi in iron deficient conditions [10][11][12][13]. Their modes of action in suppression of disease may be based on competition for iron with the pathogen [9].…”

Analysis of the Rhizobium leguminosarum siderophore-uptake gene fhuA: differential expression in free-living bacteria and nitrogen-fixing bacteroids and distribution of an fhuA pseudogene in different strains The GenBank/EMBL/DDBJ accession number for the sequence determined in this work is AJ238208.

“…viciae, the symbiont of peas, lentils, vetches and some beans, makes vicibactin, a cyclic trihydroxamate siderophore with three residues each of N#-acetyl-N&-hydroxy--ornithine and -hydroxybutyrate (Dilworth et al, 1998). Different rhizobia make other hydroxamates (Persmark et al, 1993), catechols (Roy et al, 1994), citrate (Guerinot et al, 1990) or anthranilate (Barsomonian et al, 1992).…”

Genetic Organization of the Region Encoding Regulation, Biosynthesis, and Transport of Rhizobactin 1021, a Siderophore Produced by Sinorhizobium meliloti

“…They are produced only under iron-limiting conditions, with production being negatively regulated by the Fur protein in conjunction with iron. A variety of structurally different siderophores from different strains of rhizobia have been characterized (6,14,29,41,42,47,50). The ability of Sinorhizobium (formerly Rhizobium) meliloti to take up ferrisiderophores has been correlated with the presence of specific siderophore receptor proteins in the outer membrane (46).…”