Abstract
The replication terminus region (Ter) of the unique chromosome of most bacteria locates at mid-cell at the time of cell division. In several species, this localization participates in the necessary coordination between chromosome segregation and cell division, notably for the selection of the division site, the licensing of the division machinery assembly and the correct alignment of chromosome dimer resolution sites. The genome of Vibrio cholerae, the agent of the deadly human disease cholera, is divided into two chromosomes, chrI and chrII. Previous fluorescent microscopy observations suggested that although the Ter regions of chrI and chrII replicate at the same time, chrII sister termini separated before cell division whereas chrI sister termini were maintained together at mid-cell, which raised questions on the management of the two chromosomes during cell division. Here, we simultaneously visualized the location of the dimer resolution locus of each of the two chromosomes. Our results confirm the late and early separation of chrI and chrII Ter sisters, respectively. They further suggest that the MatP/matS macrodomain organization system specifically delays chrI Ter sister separation. However, TerI loci remain in the vicinity of the cell centre in the absence of MatP and a genetic assay specifically designed to monitor the relative frequency of sister chromatid contacts during constriction suggest that they keep colliding together until the very end of cell division. In contrast, we found that even though it is not able to impede the separation of chrII Ter sisters before septation, the MatP/matS macrodomain organization system restricts their movement within the cell and permits their frequent interaction during septum constriction.
Highlights
Most bacteria harbour a single chromosome and, in the rare case in which the genetic material is divided on several chromosomes, the extra-numerous ones appear to have derived from horizontally acquired mega-plasmids that subsequently gained essential genes [1]
TerII and delayed TerI segregation Replication profiling of V. cholerae cells by deep sequencing indicated that termination most frequently occurred at a distance of,90 kbp and,70 kbp from the reference loci that had been used by Srivastava et al for the simultaneous visualization of the positions of TerI and TerII (Figure S1A, [32])
To confirm the segregation pattern of the terminus regions of chrI and chrII, we simultaneously visualized the intracellular location of dif1 and dif2 in cells that were exponentially growing in minimal media
Summary
Most bacteria harbour a single chromosome and, in the rare case in which the genetic material is divided on several chromosomes, the extra-numerous ones appear to have derived from horizontally acquired mega-plasmids that subsequently gained essential genes [1]. This is notably the case for Vibrio cholerae, the agent of the deadly human diarrheal disease cholera, whose genome is divided between a 2.961 Mbp ancestral chromosome, chrI, and a 1.072 Mbp plasmid-derived chromosome, chrII [2]. The necessary coordination between replication, chromosome segregation and cell scission raises questions on the management of the different chromosomes of such bacteria
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