GENETIC ORGANIZATION OF THE DUPLICATED VAP REGION OF THE DICHELOBACTER-NODOSUS GENOME

The recombinant plasmid pJIR318 contains a fragment of the Dichelobact er nodosus genome which is associated with virulence. Sequence analysi s of the pJIR318 insert has shown that it contains four vap (virulence -associated protein) genes which are homologous to open reading frames found on the Escherichia coli F plasmid and the Neisseria gonorrhoeae cryptic plasmid (M. E. Katz, R. A. Strugnell, and J. I. Rood, Infect. and Immun. 60:4586-4592, 1992). The plasmid pJIR318 hybridizes to thr ee regions of the D. nodosus genome, each of which has now been isolat ed. Regions 1 and 3 were found to be adjacent in the genome of D. nodo sus A198, and the order of the vap genes in vap regions 1 and 2 was sh own to be identical. Partial sequence analysis and Southern blot analy sis of the vap regions showed that the three regions probably arose by a duplication event(s) followed by insertions and/or deletions. A rec ombinant plasmid, pJIR749, was isolated from a library of a benign D. nodosus strain, 305. This plasmid contained sequences from both ends o f vap region 2. Analysis of pJIR749 showed that the sequences on eithe r side of vap region 2 were separated by 324 bp in the genome of benig n strain 305 and that the orientations of the sequences were different . It is clear that a simple insertion or deletion event did not genera te the benign and virulent strains studied. A model which describes th e evolution of the duplicated vap regions in D. nodosus A198 is presen ted.