Abstract
New pathogenic bacteria belonging to the genus Erwinia associated with pome fruit trees (Erwinia, E. piriflorinigrans, E. uzenensis) have been increasingly described in the last years, and comparative analyses have found that all these species share several genetic characteristics. Studies at different level (whole genome comparison, virulence genes, plasmid content, etc.) show a high intraspecies homogeneity (i.e., among E. amylovora strains) and also abundant similarities appear between the different Erwinia species: presence of plasmids of similar size in the pathogenic species; high similarity in several genes associated with exopolysaccharide production and hence, with virulence, as well as in some other genes, in the chromosomes. Many genetic similarities have been observed also among some of the plasmids (and genomes) from the pathogenic species and E. tasmaniensis or E. billingiae, two epiphytic species on the same hosts. The amount of genetic material shared in this genus varies from individual genes to clusters, genomic islands and genetic material that even may constitute a whole plasmid. Recent research on evolution of erwinias point out the horizontal transfer acquisition of some genomic islands that were subsequently lost in some species and several pathogenic traits that are still present. How this common material has been obtained and is efficiently maintained in different species belonging to the same genus sharing a common ecological niche provides an idea of the origin and evolution of the pathogenic Erwinia and the interaction with non-pathogenic species present in the same niche, and the role of the genes that are conserved in all of them.
Highlights
The genus Erwinia belongs to the Enterobacteriaceae family and essentially comprises plantassociated bacteria that are pathogenic and epiphytic to pome fruit trees (Palacio-Bielsa et al, 2011)
Partial sequences of plasmids present in some E. amylovora strains are most probably originated from other plasmids from human and animal pathogens and the high genetic identity between plasmids pEI70 from E. amylovora and pEB102 from the epiphytic species E. billingiae indicates that lateral transfer of almost entire extrachromosomal material could take place between species sharing host and niche and be stably maintained (Llop et al, 2011; Figure 2A)
Several of the plasmids reported show the potential for conjugal transfer, such as pEL60 and pEI70 from E. amylovora, pEB170 of E. billingiae, and several plasmids from E. tasmaniensis, and others carry mob genes and may contain an oriT to be mobilized by Tra proteins of other plasmids
Summary
Recent research on evolution of erwinias point out the horizontal transfer acquisition of some genomic islands that were subsequently lost in some species and several pathogenic traits that are still present. How this common material has been obtained and is efficiently maintained in different species belonging to the same genus sharing a common ecological niche provides an idea of the origin and evolution of the pathogenic Erwinia and the interaction with non-pathogenic species present in the same niche, and the role of the genes that are conserved in all of them
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