The pathway to resolve dimeric forms distinguishes plasmids from megaplasmids in Enterobacteriaceae.

Bacterial genomes contain a plethora of secondary replicons of divergent size. Circular replicons must carry a system for resolving dimeric forms, resulting from recombination between sister copies. These systems use site-specific recombinases.

Interplay between the Xer recombination system and the dissemination of antibioresistance in Acinetobacter baumannii.

Antibiotic-resistant infections are a pressing clinical challenge. Plasmids are known to accelerate the emergence of resistance by facilitating horizontal gene transfer of antibiotic resistance genes between bacteria. We explore this question in Acinetobacter baumannii, a globally emerging nosocomial pathogen responsible for a wide range of infections with a worrying accumulation of resistance, particularly involving plasmids.

In vivo assembly of bacterial partition condensates on circular supercoiled and linear DNA.

In bacteria, faithful DNA segregation of chromosomes and plasmids is mainly mediated by ParABS systems. These systems, consisting of a ParA ATPase, a DNA binding ParB CTPase, and centromere sites parS, orchestrate the separation of newly replicated DNA copies and their intracellular positioning. Accurate segregation relies on the assembly of a high-molecular-weight complex, comprising a few hundreds of ParB dimers nucleated from parS sites.

A subclass of the IS1202 family of bacterial insertion sequences targets XerCD recombination sites.

We describe here a new family of IS which are related to IS1202, originally isolated from Streptococcus pneumoniae in the mid-1990s and previously tagged as an emerging IS family in the ISfinder database. Members of this family have impacted some important properties of their hosts. We describe here another potentially important property of certain family members: specific targeting of xrs recombination sites.

Atypical low-copy number plasmid segregation systems, all in one?

Plasmid families harbor different maintenances functions, depending on their size and copy number. Low copy number plasmids rely on active partition systems, organizing a partition complex at specific centromere sites that is actively positioned using NTPase proteins. Some low copy number plasmids lack an active partition system, but carry atypical intracellular positioning systems using a single protein that binds to the centromere site but without an associated NTPase.

DNA Segregation in Enterobacteria.

DNA segregation ensures that cell offspring receive at least one copy of each DNA molecule, or replicon, after their replication. This important cellular process includes different phases leading to the physical separation of the replicons and their movement toward the future daughter cells. Here, we review these phases and processes in enterobacteria with emphasis on the molecular mechanisms at play and their controls.

Characterization of the DNA Binding Domain of StbA, A Key Protein of A New Type of DNA Segregation System.

Low-copy-number plasmids require sophisticated genetic devices to achieve efficient segregation of plasmid copies during cell division. Plasmid R388 uses a unique segregation mechanism, based on StbA, a small multifunctional protein. StbA is the key protein in a segregation system not involving a plasmid-encoded NTPase partner, it regulates the expression of several plasmid operons, and it is the main regulator of plasmid conjugation.

Strigolactones (SLs) modulate the plastochron by regulating KLUH (KLU) transcript abundance in Arabidopsis.

The timing of leaf emergence at the shoot apical meristem, or plastochron, is highly regulated in plants. Among the genes known to regulate the plastochron in Arabidopsis (Arabidopsis thaliana), KLUH (KLU), orthologous to the rice (Oryza sativa) PLASTOCHRON1, encodes the cytochrome P450 CYP78A5, and is thought to act through generation of a still unknown mobile signal. As klu mutants display not only a short plastochron but also a branching phenotype reminiscent of strigolactone (SL) mutants, we investigated whether KLU/CYP78A5 is involved in SL biosynthesis.

Complete Genome Sequence of Staphylococcus epidermidis PH1-28, Isolated from the Forehead of a Hyperseborrheic Donor.

We report the complete genome sequence of commensal strain PH1-28, isolated from the forehead of a healthy donor. The assembled 2.6-Mbp genome consisted of one chromosome and five plasmids.

Bacterial cell proliferation: from molecules to cells.

Bacterial cell proliferation is highly efficient, both because bacteria grow fast and multiply with a low failure rate. This efficiency is underpinned by the robustness of the cell cycle and its synchronization with cell growth and cytokinesis. Recent advances in bacterial cell biology brought about by single-cell physiology in microfluidic chambers suggest a series of simple phenomenological models at the cellular scale, coupling cell size and growth with the cell cycle.

Post-replicative pairing of sister ter regions in Escherichia coli involves multiple activities of MatP.

The ter region of the bacterial chromosome, where replication terminates, is the last to be segregated before cell division in Escherichia coli. Delayed segregation is controlled by the MatP protein, which binds to specific sites (matS) within ter, and interacts with other proteins such as ZapB. Here, we investigate the role of MatP by combining short-time mobility analyses of the ter locus with biochemical approaches.

Intracellular Positioning Systems Limit the Entropic Eviction of Secondary Replicons Toward the Nucleoid Edges in Bacterial Cells.

Bacterial genomes, organized intracellularly as nucleoids, are composed of the main chromosome coexisting with different types of secondary replicons. Secondary replicons are major drivers of bacterial adaptation by gene exchange. They are highly diverse in type and size, ranging from less than 2 to more than 1000 kb, and must integrate with bacterial physiology, including to the nucleoid dynamics, to limit detrimental costs leading to their counter-selection.

Genomewide phenotypic analysis of growth, cell morphogenesis, and cell cycle events in .

Cell size, cell growth, and cell cycle events are necessarily intertwined to achieve robust bacterial replication. Yet, a comprehensive and integrated view of these fundamental processes is lacking. Here, we describe an image-based quantitative screen of the single-gene knockout collection of and identify many new genes involved in cell morphogenesis, population growth, nucleoid (bulk chromosome) dynamics, and cell division.

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.

Mapping Topoisomerase IV Binding and Activity Sites on the E. coli Genome.

Catenation links between sister chromatids are formed progressively during DNA replication and are involved in the establishment of sister chromatid cohesion. Topo IV is a bacterial type II topoisomerase involved in the removal of catenation links both behind replication forks and after replication during the final separation of sister chromosomes. We have investigated the global DNA-binding and catalytic activity of Topo IV in E.

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.

Mechanisms for chromosome segregation.

Bacteria face the problem of segregating their gigantic chromosomes without a segregation period restricted in time and space, as Eukaryotes do. Segregation thus involves multiple activities, general or specific of a chromosome region and differentially controlled. Recent advances show that these various mechanisms conform to a “pair and release” rule, which appears as a general rule in DNA segregation.

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.

TPM analyses reveal that FtsK contributes both to the assembly and the activation of the XerCD-dif recombination synapse.

Circular chromosomes can form dimers during replication and failure to resolve those into monomers prevents chromosome segregation, which leads to cell death. Dimer resolution is catalysed by a highly conserved site-specific recombination system, called XerCD-dif in Escherichia coli. Recombination is activated by the DNA translocase FtsK, which is associated with the division septum, and is thought to contribute to the assembly of the XerCD-dif synapse.

FtsK actively segregates sister chromosomes in Escherichia coli.

Bacteria use the replication origin-to-terminus polarity of their circular chromosomes to control DNA transactions during the cell cycle. Segregation starts by active migration of the region of origin followed by progressive movement of the rest of the chromosomes. The last steps of segregation have been studied extensively in the case of dimeric sister chromosomes and when chromosome organization is impaired by mutations.

Co-evolution of segregation guide DNA motifs and the FtsK translocase in bacteria: identification of the atypical Lactococcus lactis KOPS motif.

Bacteria use the global bipolarization of their chromosomes into replichores to control the dynamics and segregation of their genome during the cell cycle. This involves the control of protein activities by recognition of specific short DNA motifs whose orientation along the chromosome is highly skewed. The KOPS motifs act in chromosome segregation by orienting the activity of the FtsK DNA translocase towards the terminal replichore junction.

A defined terminal region of the E. coli chromosome shows late segregation and high FtsK activity.

Background: The FtsK DNA-translocase controls the last steps of chromosome segregation in E. coli. It translocates sister chromosomes using the KOPS DNA motifs to orient its activity, and controls the resolution of dimeric forms of sister chromosomes by XerCD-mediated recombination at the dif site and their decatenation by TopoIV.

The terminal region of the E. coli chromosome localises at the periphery of the nucleoid.

Background: Bacterial chromosomes are organised into a compact and dynamic structures termed nucleoids. Cytological studies in model rod-shaped bacteria show that the different regions of the chromosome display distinct and specific sub-cellular positioning and choreographies during the course of the cell cycle. The localisation of chromosome loci along the length of the cell has been described.