Xylella taiwanensis sp. nov., causing pear leaf scorch disease

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Xylella, pear leaf scorch disease, Xylella taiwanensis, fastidious prokaryote

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A Gram-stain-negative, nutritionally fastidious bacterium (PLS229T) causing pear leaf scorch was identified in Taiwan and previously grouped into Xylella fastidiosa . Yet, significant variations between PLS229T and Xylella fastidiosa were noted. In this study, PLS229T was evaluated phenotypically and genotypically against representative strains of Xylella fastidiosa , including strains of the currently known subspecies of Xylella fastidiosa , Xylella fastidiosa subsp. multiplex and ‘ Xylella fastidiosa subsp. pauca ’. Because of the difficulty of in vitro culture characterization, emphases were made to utilize the available whole-genome sequence information. The average nucleotide identity (ANI) values, an alternative for DNA–DNA hybridization relatedness, between PLS229T and Xylella fastidiosa were 83.4–83.9 %, significantly lower than the bacterial species threshold of 95 %. In contrast, sequence similarity of 16S rRNA genes was greater than 98 %, higher than the 97 % threshold to justify if two bacterial strains belong to different species. The uniqueness of PLS229T was also evident by observing only about 87 % similarity in the sequence of the 16S-23S internal transcribed spacer (ITS) between PLS229T and strains of Xylella fastidiosa , discovering significant single nucleotide polymorphisms at 18 randomly selected housekeeping gene loci, observing a distinct fatty acid profile for PLS229T compared with Xylella fastidiosa , and PLS229T having different observable phenotypes, such as different susceptibility to antibiotics. A phylogenetic tree derived from 16S rRNA gene sequences showed a distinct PLS229T phyletic lineage positioning it between Xylella fastidiosa and members of the genus Xanthomonas . On the basis of these data, a novel species, Xylella taiwanensis sp. nov. is proposed. The type strain is PLS229T (=BCRC 80915T=JCM 31187T).

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International Journal of Systematic and Evolutionary Microbiology, v. 66, p. 4766-4771