Unraveling the first Xylella fastidiosa subsp. fastidiosa Genome from Texas

Xylella fastidiosa is a Gram-negative bacterial plant pathogen spread by a number of sharpshooter insect vectors including the Glassy-winged sharpshooter, Homoladisca vitripennis. Pierce’s Disease (PD) of grapevines is the result of the grape strain of the bacterium, X. fastidiosa supsp. fastidiosa growing in the xylem of the plant. PD typically results in vine death within 1 to 2 years. Several X. fastidiosa supsp. fastidiosa isolates have been sequenced from California, but in order to understand the evolutionary history of the bacterium and pathogenicity differences between populations, it was the goal of this project to sequence a genome of the Texas grape strain, GB514. Whole genome shotgun titanium pyrosequencing was performed and resulting data assembled yielding two primary contigs one of which was 2.49 megabases and represented what is predicted in this version 1 assembly to be a complete Xylella chromosome. A second notable fragment, did not assemble as part of the chromosome and could represent a possible low copy number plasmid or linear extrachromosomal DNA content. For the region that did not assemble, 39 novel genes have been identified with known functions. A BLASTn analysis of this gene collection found 94% query coverage and 98% identity to the recently uploaded plasmid pXf-RIV25 from mulberry isolate (X. fastidiosa supsp. multiplex). However, plasmid isolations of GB514, thus far, have not resulted in any detectable plasmid. Of these 39 genes identified, 11 genes code for the components of a functional Type IV secretion pathway (critical for many bacteria infecting eukaryotic hosts). The presence of these Type IV genes integrated into the Texas grape strain or on a plasmid found in two different subspecies suggests it may have a critical role in virulence.