Virulence of the plant pathogen Erwinia amylovora: a comparative proteome analysis

Abstract

Erwinia amylovora is a Gram-negative plant pathogen that is classified as member of the Enterobacteriaceae which makes it closely related to many important human and animal pathogens such as Escherichia coli, Salmonella spp., Shigella spp. and Yersinia spp. E. amylovora causes the destructive disease fire blight which affects most members of the Rosaceae family of which apple (Malus spp.) and pear (Pyrus spp.) are economically the most important species. Other hosts include quince, blackberry, raspberry and many wild and cultivated ornamentals including Cotoneaster and Pyracantha spp. This devastating disease is spread by wind, insects, birds and human activity. The absence of effective control mechanisms and its destructive character enable E. amylovora to disperse rapidly both within susceptible plants and between trees in orchards which could lead to great economic losses. Further, fire blight will become an even greater threat for the fruit production in Europe in the near future because of the expected rise in average global temperature, the growing of cultivars on susceptible rootstocks and the introduction of susceptible cultivars. Independent research has suggested that E. amylovora is a homogeneous species based on physiological, biochemical, phylogenetic and genetic analysis. Moreover, a low diversity within this pathogen has been reported following the comparison of strains locally separated leading to the hypothesis that minimal evolution has occurred since the global dispersion of this pathogen. Contradictory, differences in virulence have been observed between E. amylovora strains isolated from nature. Different factors have been identified as being crucial for virulence in E. amylovora including a functional type III secretion system (T3SS) to inject effector proteins into the cytosol of the host, exopolysaccharides (EPS) including amylovoran and levan, the sorbitol metabolism, the siderophore desferrioxamine, metalloproteases and twocomponent signal transduction systems (TCSTs). To date, an abundance of research is published based on genomic experiments although no conclusive definition has been provided to explain the difference in virulence between different isolates of E. amylovora. Because of the rather limited knowledge of the proteome of this plant pathogen, the conducted research is dedicated to the proteome of E. amylovora by comparing four strains exhibiting differences in their virulent ability. For an in-depth comparison, two strains which exhibited the most differences both during artificial infections and during the analysis of the proteome data, were used. The main goal of the current study was to identify the proteins leading to this differential virulence between different isolates of E. amylovora. We wanted to expand our knowledge concerning the proteome of E. amylovora. Therefore, a proteomics analysis by two-dimensional differential in gel electrophoresis (2DDIGE) for E. amylovora has been optimized.