ISOLATION BY GENOMIC SUBTRACTION OF DNA PROBES SPECIFIC FOR ERWINIA-CAROTOVORA SUBSP ATROSEPTICA

Erwinia carotovora subsp. atroseptica is a pathogen of potatoes in Eur ope because of its ability to induce blackleg symptoms early in the gr owing season. However, E. carotovora subsp. carotovora is not able to produce such severe symptoms under the same conditions. On the basis o f the technique described by Straus and Ausubel (Proc. Natl. Acad. Sci . USA 87:1889-1893, 1990), we isolated DNA sequences of E. carotovora subsp. atroseptica 86.20 that were absent from the genomic DNA of E. c arotovora subsp. carotovora CH26. Six DNA fragments ranging from ca. 1 80 to 400 bp were isolated, cloned, and sequenced. Each fragment was f urther hybridized with 130 microorganisms including 87 E. carotovora s trains. One probe was specific for typical E. carotovora subsp. atrose ptica strains, two probes hybridized with all E. carotovora subsp. atr oseptica strains and with a few E. carotovora subsp. carotovora strain s, and two probes recognized only a subset of E. carotovora subsp. atr oseptica strains. The last probe was absent from the genomic DNA of E. carotovora subsp. carotovora CH26 but was present in the genomes of m any strains, including those of other species and genera. This probe i s homologous to the putP gene of Escherichia coli, which encodes a pro line carrier. Further use of the probes is discussed.