Xylella fastidiosa subspecies: X. fastidiosa subsp. [correction] fastidiosa [correction] subsp. nov., X. fastidiosa subsp. multiplex subsp. nov., and X. fastidiosa subsp. pauca subsp. nov.
Xylella fastidiosa, a fastidious bacterium causing disease in over 100 plant species, is classified as a single species, although genetic studies support multiple taxons. To determine the taxonomic relatedness among strains of X. fastidiosa, we conducted DNA-DNA relatedness assays and sequenced the 16S-23S intergenic spacer (ITS) region using 26 strains from 10 hosts. Under stringent conditions (Tm -15 degrees C), the DNA relatedness for most X. fastidiosa strains was *70%. However, at high stringency (Tm -8 degrees C), three distinct genotypes (A, B, and C) were revealed. Taxon A included strains from cultivated grape, alfalfa, almond (two), and maple, interrelated by 85% (mean); taxon B included strains from peach, elm, plum, pigeon grape, sycamore, and almond (one), interrelated by 84%; and taxon C included only strains from citrus, interrelated by 87%. The mean reciprocal relatedness between taxons A and B, A and C, and B and C, were 58, 41, and 45%, respectively. ITS results also indicated the same grouping; taxons A and B, A and C, and B and C had identities of 98.7, 97.9, and 99.2%, respectively. Previous and present phenotypic data supports the molecular data. Taxon A strains grow faster on Pierce's disease agar medium whereas B and C strains grow more slowly. Taxon B and C strains are susceptible to penicillin and resistant to carbenicillin whereas A strains are opposite. Each taxon can be differentiated serologically as well as by structural proteins. We propose taxons A, B, and C be named X. fastidiosa subsp. fastidiosa [correction] subsp. nov, subsp. multiplex, subsp. nov., and subsp. pauca, subsp. nov., respectively. The type strains of the subspecies are subsp. fastidiosa [correction] ICPB 50025 (= ATTC 35879T and ICMP 15197), subsp. multiplex ICPB 50039 (= ATTC 35871 and ICMP 15199), and subsp. pauca ICPB 50031 (= ICMP 15198).
Schaad
Norman W
NW
ARS-USDA, Foreign Disease-Weed Science Research Unit, Ft. Detrick, MD 21702, USA. Schaad@ncifcrf.gov
Postnikova
Elena
E
Lacy
George
G
Fatmi
M'Barek
M
Chang
Chung-Jan
CJ
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000032:analysis; D001483:Base Sequence; D002228:Carbenicillin / Q000494:pharmacology; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000302:isolation & purification; D005838:Genotype; D008969:Molecular Sequence Data; D010406:Penicillins / Q000494:pharmacology; D010944:Plants / Q000382:microbiology*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D012703:Serotyping; D044366:Transition Temperature; D044167:Xylella / Q000145:classification* / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification / Q000378:metabolism
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D021903:DNA, Ribosomal Spacer; D010406:Penicillins; D002228:Carbenicillin