Acceptance by Erwinia spp. of R Plasmid R68.45 and Its Ability to Mobilize the Chromosome of Erwinia chrysanthemi†

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R plasmid R68.45 was transferred in broth matings from Escherichia coli to strains of Erwinia amylovora, E. carotovora subsp. atroseptica, E. chrysanthemi, and E. herbicola (Enterobacter agglomerans); the frequency of transfer ranged from 2 × 10−8 to 5 × 10−4 per input donor cell depending on the bacterial species. The drug resistance markers tet+, amp+, and kan+ were stable in these Erwinia species. Transconjugants of Erwinia spp., but not of the wild-type parent Erwinia strains, acquired levels of antibiotic resistance (tetracycline, 50 μg/ml; ampicillin, 200 μg/ml; kanamycin 200 μg/ml) similar to those of the donor R68.45-bearing strain of Escherichia coli. Erwinia transconjugants (with one exception of E. carotovora subsp. atroseptica) were donors of the antibiotic resistance markers; the frequency of transfer was consistently higher with an E. coli strain than with Erwinia spp. as recipients, and when matings were done on a solid surface (membranes) rather than in liquid. Transfer of chromosomal markers ade+, gal+, gtu+ (utilization of galacturonate), his+, leu+, lys+, thr+, and trp+ occurred in crosses between E. chrysanthemi strains harboring R68.45 and appropriate recipient strains; the frequency of transfer ranged from 9.0 × 10−8 to 2.0 × 10−6 depending on the selective marker. Analysis of the coinheritance of unselected markers among various classes of recombinants revealed linkage between thr-leu-lys-ade and between trp and his, thus confirming earlier findings with the Hfr-type donor cells. Since R68.45 mobilized an array of chromosomal markers in the wild-type as well as genetically marked strains of E. chrysanthemi, the system, used in conjunction with the existing Hfr strains, should provide a useful tool to study the genetics of plant pathogenicity of this bacterial species. In contrast to E. chrysanthemi, R68.45 did not mobilize chromosomal markers ilv+, his+, rbs+, ser+, and thr+ in E. amylovora EA178.

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