IDENTIFICATION OF A GENE ENCODING A BACTERIOPHAGE-RELATED INTEGRASE IN A VAP REGION OF THE DICHELOBACTER-NODOSUS GENOME

Dichelobacter nordosus is the principal causative agent of ovine footr ot. Nucleotide (nt) sequences from the D. nodosus genome have been iso lated and a series of overlapping lambda clones defining vap (virulenc e-associated protein) regions 1, 2 and 3 have been reported [Katz et a l., J. Bacteriol. 176 (1994) 2663-2669]. In the present study, the lim its of the virulence-associated (va) DNA around vap regions 1 and 3 we re determined by dot-blot hybridization experiments using plasmid subc lones to probe genomic DNA from the D. nodosus virulent strain A198 an d the benign strain C305. This va region was found to be approx. 11.9 kb in length, and to be interrupted by a short DNA segment which is al so found in the benign D. nodosus strain. Sequence analysis of the ent ire region revealed an ORF, intA, which is very similar to the integra ses of bacteriophages phi R73, P4 and Sf6. Bacteriophages phi R73 and P4 integrate into the 3' ends of tRNA genes, with the integrase genes adjacent to the tRNA genes. A similar arrangement was found in the D. nodosus va region. A 19-bp nt sequence was found to be repeated at the ends of the va region, and may represent the bacteriophage attachment site. These findings suggest that D. nodosus may have acquired these DNA sequences by the integration of a bacteriophage, or an integrative plasmid that contains a bacteriophage-related integrase gene. The hig h similarity of the D. nodosus integrase to integrases from coliphages suggests that these va sequences may be transferred between distantly related bacteria. Integration of the putative bacteriophage was follo wed by at least two independent duplication events.