Genomic insights into the diversity of European Xylella fastidiosaisolates

A growing number of recent and current studies on Xylella fastidiosa outbreaks in Europe emphasise genomic sequencing of bacterial isolates as a mean to infer their potential origin, biology, recombination events and possible determinants of host specificity. In the present work we have undertaken a re-assessment of publicly available X. fastidiosa genomic sequences from a comparative standpoint. With limitations due to the fact that most of the available sequences were left at the draft stage, and that only a few are complete, we undertook to compare: i) genomic organisation (synteny); ii) number, origin and genomic position of insertion elements (IS, islands, phage-related elements, plasmids); iii) individual gene complements within the species and subspecies pan-genomes; and iv) exclusive or enriched genes associated with subspecies or host of isolation. Our preliminary results suggest that X. fastidiosa genomes show a great plasticity in their organisation, possibly aided by the widespread presence of insertion elements, and that the traditional subspecies classification, although useful from an operational standpoint, is probably insufficient to explain the observed genomic variability.