Dynamic transitions of initiator binding coordinate the replication of the two chromosomes in Vibrio cholerae.

The replication of the two chromosomes in the pathogenic bacterium Vibrio cholerae is coordinated by the binding of initiator protein RctB to a checkpoint sequence, crtS. Replication of crtS on the primary chromosome (Chr1) triggers replication of the secondary chromosome (Chr2), but the details are poorly understood. Here, we analyze RctB binding patterns in the V.

DNA methylation by CcrM contributes to genome maintenance in the Agrobacterium tumefaciens plant pathogen.

The cell cycle-regulated DNA methyltransferase CcrM is conserved in most Alphaproteobacteria, but its role in bacteria with complex or multicentric genomes remains unexplored. Here, we compare the methylome, the transcriptome and the phenotypes of wild-type and CcrM-depleted Agrobacterium tumefaciens cells with a dicentric chromosome with two essential replication origins. We find that DNA methylation has a pleiotropic impact on motility, biofilm formation and viability.

Cassette recombination dynamics within chromosomal integrons are regulated by toxin-antitoxin systems.

Integrons are adaptive bacterial devices that rearrange promoter-less gene cassettes into variable ordered arrays under stress conditions, thereby sampling combinatorial phenotypic diversity. Chromosomal integrons often carry hundreds of silent gene cassettes, with integrase-mediated recombination leading to rampant DNA excision and integration, posing a potential threat to genome integrity. How this activity is regulated and controlled, particularly through selective pressures, to maintain such large cassette arrays is unknown.

Cassette recruitment in the chromosomal Integron of Vibrio cholerae.

Integrons confer a rapid adaptation capability to bacteria. Integron integrases are able to capture and shuffle novel functions embedded in cassettes. Here, we investigated cassette recruitment in the Vibrio cholerae chromosomal integron during horizontal transfer.

Vibrio cholerae chromosome 2 copy number is controlled by the methylation-independent binding of its monomeric initiator to the chromosome 1 crtS site.

Bacteria contain a primary chromosome and, frequently, either essential secondary chromosomes or dispensable megaplasmids of plasmid origin. Incoming plasmids are often poorly adapted to their hosts and their stabilization requires integration with the host's cellular mechanisms in a process termed domestication. All Vibrio, including pathogenic species, carry a domesticated secondary chromosome (Chr2) where replication is coordinated with that of the primary chromosome (Chr1).

Replicate Once Per Cell Cycle: Replication Control of Secondary Chromosomes.

Faithful vertical transmission of genetic information, especially of essential core genes, is a prerequisite for bacterial survival. Hence, replication of all the replicons is tightly controlled to ensure that all daughter cells get the same genome copy as their mother cell. Essential core genes are very often carried by the main chromosome.

FtsK translocation permits discrimination between an endogenous and an imported Xer/dif recombination complex.

In bacteria, the FtsK/Xer/dif (chromosome dimer resolution site) system is essential for faithful vertical genetic transmission, ensuring the resolution of chromosome dimers during their segregation to daughter cells. This system is also targeted by mobile genetic elements that integrate into chromosomal dif sites. A central question is thus how Xer/dif recombination is tuned to both act in chromosome segregation and stably maintain mobile elements.

Resolution of Multimeric Forms of Circular Plasmids and Chromosomes.

One of the disadvantages of circular plasmids and chromosomes is their high sensitivity to rearrangements caused by homologous recombination. Odd numbers of crossing-over occurring during or after replication of a circular replicon result in the formation of a dimeric molecule in which the two copies of the replicon are fused. If they are not converted back to monomers, the dimers of replicons may fail to correctly segregate at the time of cell division.

The FtsK family of DNA translocases finds the ends of circles.

A global view of bacterial chromosome choreography during the cell cycle is emerging, highlighting as a next challenge the description of the molecular mechanisms and factors involved. Here, we review one such factor, the FtsK family of DNA translocases. FtsK is a powerful and fast translocase that reads chromosome polarity.