LARGE GENOME REARRANGEMENTS DISCOVERED BY THE DETAILED ANALYSIS OF 21PSEUDOMONAS-AERUGINOSA CLONE-C ISOLATES FOUND IN ENVIRONMENT AND DISEASE HABITATS

In order to determine primary genetic events which occur during the di versification of a Pseudomonas aeruginosa clone in natural habitats, c omparative genome analysis of 21 isolates of a predominant clone, call ed clone C, derived mainly fi om patients with cystic fibrosis (CF) an d the aquatic environment, was carried out. Physical chromosome maps w ere constructed for the restriction enzymes SpeI, PacI, SwaI and I-Ceu I by one and two-dimensional pulsed-field gel electrophoresis and by c omparison with the existing strain C map. The positioning of 26 genes generated the genetic maps. Chromosome size varied between 6345 and 66 06 kilobase-pairs (kb). A plasmid of 95 kb was detected in the strains of non-CF origin and, in addition, was found to be integrated into th e chromosome of all strains but one CF isolate. Four subgroups of clon e C strains were discriminated by the acquisition and loss of large bl ocks of DNA that could cover more than 10% of the chromosome size. The exchange of DNA blocks which ranged in size from 1 kb to 214 kb occur red preferentially around the terminus of replication region which is poor in biosynthetic genes. Genetic material which was additionally in troduced into strain C in comparison with strain PAO seems to be a tar get of mutational processes in clone C strains. Within and among subgr oups CF isolates frequently exhibited large inversions affecting the w hole chromosomal structure. We concluded that the exchange of DNA bloc ks by mechanisms of horizontal transfer and large chromosomal inversio ns are major factors leading to the divergence of a clone in the speci es P. aeruginosa. (C) 1997 Academic Press Limited.