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Oral: 16th I.E., Melhus


Complete genome sequences of Xanthomonas axonopodis pv. phaseoli and X. fuscans subsp. fuscans generated by long-read sequence technology
M. O'LEARY (1), G. Coaker (1), R. Gilbertson (1) (1) University of California, Davis, U.S.A.

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Common bacterial blight, caused by Xanthomonas axonopodis pv. phaseoli (Xap) and X. fuscans subsp. fuscans (Xff), is a globally important disease of common bean. Despite causing identical symptoms, Xap and Xff are genetically and phenotypically distinct species. No race structure exists for common bean, although pathogenic variability has been observed, particularly for Xap. To assess the relationship among these bacteria, five Xap and three Xff isolates representative of global diversity were selected for whole-genome sequencing using the Pacific Biosciences RSII platform. Complete genomes of all eight isolates were ~5 Mb, with a single chromosome and one to three plasmids. One plasmid is conserved among all isolates, whereas a second was conserved in the three globally predominant Xap and all Xff isolates. Genomic rearrangements between Xap and Xff isolates are consistent with these representing genetically distinct species. A brown diffusible pigment, produced in culture by Xff strains as the result of secretion and oxidation of homogentisic acid, was associated with a frameshift in the gene encoding homogentisate dioxygenase (hmgA). Deletion of the hmgA from Xap isolates lacking this mutation resulted in brown pigment production, whereas complementation of a Xff isolate with a functional hmgA reduced pigment production substantially. This provides biological evidence that brown pigment production in Xff is due to the lack of a functional hmgA gene.