IDENTIFICATION OF A NATIVE DICHELOBACTER-NODOSUS PLASMID AND IMPLICATIONS FOR THE EVOLUTION OF THE VAP REGIONS

Studies on the role of various virulence factors of the ovine pathogen , Dichelobacter nodosus, have suffered from the absence of a mechanism for the introduction of DNA into this organism. As an initial step in the development of genetic methods, we have identified and cloned a n ative 10-kb plasmid, pJIR896, from a clinical isolate. This plasmid wa s found to be a circular form of vap region 1/3 that is found in the r eference strain, A198. However, pJIR896 lacked the duplicated region p resent in the A198 sequence and instead contained a 1.7-kb putative in sertion sequence, IS1253, which shared similarity to a number of unusu al IS elements. A model is proposed for the evolution of vap region 1/ 3 which involves the integration of a plasmid, such as pJIR896, and su bsequent rearrangements resulting from the deletion or transposition o f IS1253.