IRON ACQUISITION AND VIRULENCE IN ERWINIA AMYLOVORA

Amongst multiple factors involved in bacterial virulence, iron acquisition is known to be important in several animal models.
In plant pathogenesis, competition for iron has been clarified with the soft rot pathogen Erwinia chrysanthemi. Erwinia amylovora CFBP1430 was shown to produce hydroxamate-type siderophores structurally characterized as deferrioxamine E essentially and traces of its analogues deferrioxamines G1 and D2. By insertional mutagenesis, several siderophore biosynthetic and transport mutants were isolated.
The transport mutant appeared to be affected in the outer membrane receptor of the ferrisiderophore.
From a wild type gene library, we isolated two recombinant cosmid clones which restore the transport mutant to wild type.
Both cosmids also conferred the ability to utilize ferrioxamine E and B as an iron source, on a FhuE E. coli mutant lacking the specific ferrioxamine receptor.
This correlated with the production of an additional polypeptide migrating in the 70,000 Daltons range in the outer membrane of transconjugants thus showing that this protein in E. amylovora serves the ferrioxamine receptor function.

The pathogenic behaviour of the mutants was tested on potted apple trees and on apple flowers which represent the natural route for infection by the pathogen.
The virulence of mutants was shown to be considerably reduced in the flower assay, thus indicating there is less available iron for bacterial growth in flowers than in vegetative parts of the plant.

VII International Workshop on Fire Blight

A. Dellagi, J. Laurent, D. Expert, J.P. Paulin, R. Kachadourian, G. Kunesh

https://doi.org/10.17660/ActaHortic.1996.411.41