GENOME STRUCTURE AND PHYLOGENY IN THE GENUS BRUCELLA

PacI and SpeI restriction maps were obtained for the two chromosomes o f each of the six species of the genus Brucella: B. melitensis, B. abo rtus, B. suis, B. canis, B. ovis, and B. neotomae. Three complementary techniques were used: hybridization with the two replicons as probes, cross-hybridization of restriction fragments, and a new mapping metho d, For each type strain, a unique I-SceI site was introduced in each o f the two replicons, and the location of SpeI sites was determined by linearization at the unique site, partial digestion, and end labeling of the fragments, The restriction and genetic maps of the six species were highly conserved. However, numerous small insertions or deletions , ranging from 1 to 34 kh, were observed by comparison with the map of the reference strain of the genus, B. melitensis 16M. A 21-kb SpeI fr agment specific to B. ol is was found in the small chromosome of this species, A 640-kb inversion was demonstrated in the B. abortus small c hromosome. All of these data allowed the construction of a phylogeneti c tree, which reflects tile traditional phenetic classification of the genus.