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

Abstract

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 Xylellafastidiosa were noted. In this study, PLS229T was evaluated phenotypically and genotypically against representative strains of Xylellafastidiosa, including strains of the currently known subspecies of Xylellafastidiosa, Xylella fastidiosa subsp. multiplex and 'Xylella fastidiosasubsp.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 Xylellafastidiosa 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 Xylellafastidiosa, discovering significant single nucleotide polymorphisms at 18 randomly selected housekeeping gene loci, observing a distinct fatty acid profile for PLS229T compared with Xylellafastidiosa, 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 Xylellafastidiosa 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).

Natural Competence Rates Are Variable Among Xylella fastidiosa Strains and Homologous Recombination Occurs In Vitro Between Subspecies fastidiosa and multiplex

“…In recent years, emergence of X. fastidiosa diseases has been reported in new host plants and geographic locations (Chang et al 2009;Martelli et al 2016;Su et al 2013), with the host range expanding to 359 plant species in 75 botanical families (European Food Safety Authority 2016). Taxonomically, X. fastidiosa strains worldwide were classified under a single species, but recently, another species was described for Taiwanese strains causing pear leaf scorch (Su et al 2016). Studies based on multilocus sequence typing and analysis (MLST/MLSA) have proposed five subspecies within X. fastidiosa (Nunney et al 2014a;Scally et al 2005), i.e., subsp.…”

Update of the Xylella spp. host plant database

“…in 1987 with the name of Xylella fastidiosa . In 2016, X. taiwanensis – a new species within the Xylella genus – was proposed (Su et al., ). The X. fastidiosa species is divided into at least six genetically different subspecies but only the subspecies fastidiosa and multiplex are officially considered viable by the International Society of Plant Pathology Committee on the Taxonomy of Plant Pathogenic Bacteria (ISPP‐CTPPB) (Bull et al., ).…”

“…Xylella taiwanensis was recorded only in one publication (Su et al., ) naturally infecting Pyrus pyrifolia in Taiwan.…”

Xylella fastidiosa: Host Range and Advance in Molecular Identification Techniques

“…It is therefore conceivable that, due to the continuous gene flow by IHR among different X. fastidiosa subspecies, in the future it will become more and more difficult to determine a clear distinction between subspecies. As a matter of fact, a new subspecies of X. fastidiosa was recently described in pears and grapevine in Taiwan (Su et al, 2012, 2013, 2016; Almeida and Nunney, 2015). However, additional genetic typing is needed to fully support the recognition of this new subspecies and to further study the isolates in Taiwan (Nunney et al, 2012; Retchless et al, 2014).…”