Genome rearrangements in salmonella enterica serovar typhi

Abstract

The order of core genes on the chromosomes of Escherichia coli K12 and of Salmonella enterica serovar Typhimurium LT2 is strongly conserved. However, the chromosome of Salmonella enterica serovar Typhi is rearranged due to homologous recombination between the rrn operons. PCR analysis detected the exact order and orientation of the seven I-Ceul fragments between operons in 136 independent wild-type strains of S. Typhi. Rearrangements within cultures of S. Typhi are common but cells with rearrangements are lost from culture. However, in spite of many rearrangements in S. Typhi, the PCR data support both the genome balance and gene dosage hypotheses for genome conservation. SARB63, a wild-type S. Typhi strain, has an unbalanced genome and a reduced growth rate in LB medium, whereas the revertents produced from SARB63 are rearranged back towards genomic balance and also have improved growth rates. Comparison of the sequenced strains of enteric bacteria for the terminus region suggests Dif as an important site in the terminus region.