The ability of Xylella fastidiosa (Xf) to acquire new genetic information, via horizontal gene transfer and homologous recombination, has been related with its capacity to colonize new hosts and environments. In this study we have performed a comparative genome analysis of the complete circularized sequences of two Xf subsp. multiplex ST6 strains (ESVL and IVIA5901) isolated from almond trees showing almond leaf scorch (ALS) symptoms, located at the Guadalest Valley in Alicante province, in mainland Spain. Genome differences detected between both strains and with the reference strain Temecula1 of Xf subsp. fastidiosa ST1 were then related with phenotypic traits differences associated to infection and disease development observed among those strains. Genome analysis of both strains indicated an average nucleotide identity at the chromosomal level of 99.99%, but main differences were due to the presence of plasmids pXF64-Hb_ESVL and pUCLA-ESVL only present in the ESVL strain. Our results showed that the ESVL strain had a higher cell motility and a greater surface attachment capability being able to form larger aggregates, while IVIA5901 strain showed a higher planktonic growth. Despite the high genetic similarity between the two strains, we have found important differences in their genomes. The presence of the two plasmids in the ESVL strain provided 48 unique genes to ESVL strain. Also, when comparing the two chromosomes, some unique genes and SNPs differences were found associated to genes potentially related with adhesion, motility, cell wall degradation, toxin-antitoxin system and the development of outer membrane protein, which might have an influence on some of the studied traits associated to pathogenicity.

Study supported by Projects XF-ACTORS 727987 (EU-H2020), AGL2016-75606-R (MICINN Spain and FEDER-EU) and COST Action CA16107 EuroXanth.