Proferrioxamine profiles of Erwinia herbicola and related bacteria

Two strains of Erwinia herbicola effective in the biocontrol of E. amylovora, the etiological agent of fire blight, were screened for proferrioxamine siderophores by on-line liquid chromatography-electrospray mass spectrometry (LC-MS). Type strains of E. herbicola and Pantoea species were included in this study for taxonomic comparisons. Proferrioxamine profiles similar to that previously described for E. amylovora, including tri- and tetrameric hydroxamates and diaminopropane-containing proferrioxamines, were observed for P. agglomerans, but not for other E. herbicola-like species. Biocontrol activity was not correlated with proferrioxamine synthesis. The results of this study are consistent with the notion that some, but not all, biocontrol strains may inhibit E. amylovora via competition for iron. Further studies into the link between biocontrol of fire blight and siderophores are thus warranted. This study also revealed limitations of standard nutrient utilization and fatty acid profile analyses for the differentiation of P. agglomerans, P. dispersa and other E. herbicola-like species from each other. Given these limitations, LC-MS may become a much needed additional diagnostic tool for the identification of E. herbicola-like strains at the species level.