Chromosomal Rearrangements Formed by rrn Recombination Do Not Improve Replichore Balance in Host-Specific Salmonella enterica Serovars

T David Matthews,Robert Edwards,Stanley Maloy

doi:10.1371/journal.pone.0013503

T David Matthews, Robert Edwards + Show 1 more

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https://doi.org/10.1371/journal.pone.0013503

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Journal: PloS one	Publication Date: Oct 19, 2010
Citations: 76	License type: CC BY 4.0

Affiliation: San Diego State University, Argonne National Laboratory

Abstract

BackgroundMost of the ∼2,600 serovars of Salmonella enterica have a broad host range as well as a conserved gene order. In contrast, some Salmonella serovars are host-specific and frequently exhibit large chromosomal rearrangements from recombination between rrn operons. One hypothesis explaining these rearrangements suggests that replichore imbalance introduced from horizontal transfer of pathogenicity islands and prophages drives chromosomal rearrangements in an attempt to improve balance.Methodology/Principal FindingsThis hypothesis was directly tested by comparing the naturally-occurring chromosomal arrangement types to the theoretically possible arrangement types, and estimating their replichore balance using a calculator. In addition to previously characterized strains belonging to host-specific serovars, the arrangement types of 22 serovar Gallinarum strains was also determined. Only 48 out of 1,440 possible arrangement types were identified in 212 host-specific strains. While the replichores of most naturally-occurring arrangement types were well-balanced, most theoretical arrangement types had imbalanced replichores. Furthermore, the most common types of rearrangements did not change replichore balance.Conclusions/SignificanceThe results did not support the hypothesis that replichore imbalance causes these rearrangements, and suggest that the rearrangements could be explained by aspects of a host-specific lifestyle.

Highlights

Numerous examples of large-scale chromosomal rearrangements between different strains of the same species or closely related species have been identified [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
Results rrn Arrangement Types Due to the factorial aspect of the total number of arrangements possible by recombination between rrn operons, it is easier to describe the rearrangements in terms of numbers instead of letters
The conserved chromosome arrangement type found in the broad host range serovars is described as arrangement type 1234567 instead of genome type 1 with an I-CeuI fragment order of BCDEFG and an A+/C+ orientation

Summary

Introduction

Numerous examples of large-scale chromosomal rearrangements between different strains of the same species or closely related species have been identified [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. Some features of chromosome organization that affect plasticity include the frequency of multiple homologous sequences on the chromosome, gene location and dosage [17,18,19,20,21], orientation of polarized sequence motifs such as ter sites and KOPS (used to terminate DNA replication and direct DNA shuffling by FtzK repectively) [22,23,24,25], and the organization of chromosomal macrodomains [22,25] Another aspect of chromosomal organization that may limit plasticity is replichore balance [26,27]. One hypothesis explaining these rearrangements suggests that replichore imbalance introduced from horizontal transfer of pathogenicity islands and prophages drives chromosomal rearrangements in an attempt to improve balance

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Conclusion