|SU, C - Taiwan Agricultural Chemicals And Toxic Substances Research Institute|
|DENG, W - National Chung-Hsing University|
|JAN, F - National Chung-Hsing University|
|CHANG, C - University Of Georgia|
|HUANG, H - University Of South Florida|
Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2016
Publication Date: 8/16/2016
Citation: Su, C.C., Deng, W.L., Jan, F.J., Chang, C.J., Huang, H., Chen, J. 2016. Xylella taiwanensis sp. nov. cause of pear leaf scorch disease in Taiwan. International Journal of Systematic and Evolutionary Microbiology. 66:4766-4771.
Interpretive Summary: Xylella fastidiosa is group of difficult to culture, xylem-limited plant pathogenic bacteria. Although most members in the group were found in the Americas, a few new members have been reported from other continents such as Asia that required further studies. Currently, an experiment known as DNA-DNA hybridization (DDH) is used to classify bacterial species, but DDH is too labor-intensive with a limited capacity to analyze Xylella. This study utilized a new method, called Average Nucleotide Index (ANI), to analyze 17 whole genome sequences of X. fastidiosa including a pear leaf scorch (PLS) strain from Taiwan. ANI analyses supported the current grouping of all American strains into a single species, X. fastidiosa; were able to define the bacterial subspecies; and provided evidence to establish a new species, X. taiwanensis, for the PLS members from Taiwan. New information from this study will have significant impact on future classification and identification of the bacteria, with direct implications for management and needed regulations for these plant pathogens.
Technical Abstract: Xylella fastidiosa is a group of xylem-limited and nutritionally fastidious plant pathogenic bacteria. While mostly found in the Americas, new X. fastidiosa strains have been reported from other continents such as Asia, including a pear leaf scorch (PLS) strain from Taiwan. Current taxonomy of X. fastidiosa is anchored around whole genome DNA-DNA hybridization (DDH) relatedness, a long-time gold standard for bacterial species delineation. Yet, DDH is labor intensive and its use for analyses of fastidious prokaryotes is limited or even prohibitive. Recent development of next generation sequencing (NGS) has led to a rapid increase of bacterial whole genome sequences in public databases. The current GenBank database (Release 204.0) has 17 whole genome sequences of X. fastidiosa including the type strain PCE-RR (ATCC 35879) and a PLS strain, PLS229. For substitution of DDH in bacterial taxonomy study, Average Nucleotide Index (ANI), calculated from whole genome sequence comparisons, has been introduced. In this study, ANI values were calculated from available whole genome sequences of strains of Xylella and evaluated for their taxonomical significance. Substantiated by the sequence analyses of 16S rRNA gene and 16S-23S intergenic spacer (ITS), ANI analyses support the current taxonomic grouping of all American Xylella strains into a single species X. fastidiosa (ANI>95); identified thresholds that could be used to define subspecies; and delineated a new species, X. taiwanensis, for the PLS strain from Taiwan.