Large chromosomal inversions occur in Pseudomonas aeruginosa clone C strains isolated from cystic fibrosis patients.

An analysis of the chromosomal structure of 21 Pseudomonas aeruginosa clone C genotypes of various origins was carried out. The circular chromosomes showed various insertions and deletions which did not alter the gene order in 6 environmental and one ear isolate in comparison with strain PAO and strain C. However, the chromosome structure differed by at least one large inversion in 50% of the genotypes (7/14) isolated from cystic fibrosis patients. Recombination endpoints were scattered throughout the chromosome. All but one inversion included the terminus of replication which was displaced by the recombination events. The rearrangements shifted the positions of the rrn operons with respect to the origin of replication, but the transcription of the rrn operons remained in the same direction as replication. The exclusive detection of inversions in isolates from cystic fibrosis lungs, which represent an atypical habitat for P. aeruginosa, supports the theory that peculiar features of this new ecological niche may select, cause or tolerate genomic changes.