Mobility shapes plasmid GC content evolution

Plasmids are frequently AT-rich relative to their bacterial hosts. Despite this tendency towards lower GC content, plasmid and host chromosome GC content are positively correlated across diverse collections of plasmid-host pairs. However, the evolutionary processes underlying this pattern remain unclear. The classic model of amelioration predicts that horizontally acquired DNA gradually converges on host nucleotide composition. However, because plasmids can repeatedly transfer between bacterial hosts, the opportunity for such host-associated evolution may depend on their transmission dynamics. Using 50,936 plasmid-host pairs from a public sequence database, we found that the apparent global correlation between plasmid and host chromosome GC content was largely driven by differences between bacterial species rather than within species. We therefore accounted for plasmid and host population structure when testing how plasmid mobility shaped host-associated compositional evolution. We compared two contrasting regimes: a population of 3,682 Enterobacterales plasmids distributed across diverse host backgrounds, and six long-term host-associated plasmids from a Rhizobium leguminosarum lineage with INSeq-determined gene essentiality data. In the Enterobacterales population, GC content variation was overwhelmingly explained by plasmid lineage rather than host phylogeny, and conjugative plasmids showed greater similarity to their host chromosomes than mobilisable or non-mobilisable plasmids. In the Rhizobium leguminosarum plasmids, synonymous-site composition was more similar to the host chromosome among genes required across multiple host life stages. Together, these results support a model in which plasmid mobility influences the opportunity for host-associated evolutionary processes to alter nucleotide composition. ### Competing Interest Statement The authors have declared no competing interest. Wellcome Trust, 319534/Z/24/Z St. John's College, University of Oxford, UK

doi.org

Resistance potentiators: Evolutionary catalysts of antibiotic resistance

How do bacteria evolve resistance to antibiotics? Drawing on evidence from experimental evolution, pathogen genomics, and molecular microbiology, this Essay argues that the evolution of antibiotic res...

journals.plos.org

Spain's largest research organization confronts its dark past

Spanish National Research Council, established under Francisco Franco’s dictatorship, has published the stories of some 500 researchers and support staff purged after civil war

science.org

Widespread immune systems protect bacteria against conjugative plasmids

Conjugative plasmids are a class of mobile genetic elements capable of efficient transfer between bacterial cells. Although they can introduce beneficial traits such as antibiotic resistance to recipi...

biorxiv.org

biorxiv.org

Beyond resistance and tolerance: rethinking evolutionary responses to antibiotics from the perspective of individual bacterial cells

Nature Communications - Beyond resistance and tolerance: rethinking evolutionary responses to antibiotics from the perspective of individual bacterial cells

rdcu.be

Rapid adaptation accelerates competitive suppression in a parasite community

Abstract. Environmental stress leads to changes in community composition by altering competitive hierarchies and pushing taxa towards extinction. Parasites

academic.oup.com

A plasmid-encoded H-NS protein selectively binds its own plasmid

H-NS is an abundant nucleoid-associated protein found in Enterobacterales species. Some conjugative plasmids encode H-NS homologues, which are thought to facilitate plasmid maintenance and reduce the ...

biorxiv.org

Modelling the role of the microbiome in antimicrobial resistance across scales - Nature Microbiology

The microbiome plays a significant yet underexplored role in antimicrobial resistance by influencing ecological and evolutionary processes. This Perspective proposes a framework to integrate microbiom...

nature.com

Mechanistic origins and evolutionary erosion of collateral sensitivity in a β-lactamase

As antibiotic discovery stalls, exploiting collateral sensitivity, where resistance to one drug increases sensitivity to another, offers a promising r…

sciencedirect.com

Eco-evolutionary responses to plasmid-dependent phage constrain the spread of multidrug-resistance plasmids

Abstract. Phage therapy offers an alternative to antibiotics for treating multidrug-resistant infections. Plasmid-dependent phages (PDPs) are promising the

academic.oup.com

De novo promoters emerge more readily from random DNA than from genomic DNA

Promoters emerge three times more readily from random DNA than from genomic DNA.

science.org

doi.org

Revisiting the life cycle of temperate phages

Nature Reviews Microbiology, Published online: 20 May 2026; doi:10.1038/s41579-026-01318-7The life cycle of temperate bacteriophages involves lytic or lysogenic cycles and has historically served as a model for studying genetic regulation. This Review provides an updated overview of these cycles and highlights their complexities, supporting a greater appreciation of the ecological roles of temperate phages.

dlvr.it

biorxiv.org

evoldir.net

Eco-evolutionary responses to plasmid-dependent phage constrain the spread of multidrug resistance plasmids

Abstract. Phage therapy offers a promising alternative to antibiotics for treating multidrug-resistant infections. Plasmid-dependent phages (PDPs) are part

doi.org

Repurposing a chromosome segregation ParB-CTPase fold into an ATPase toxin for contact-dependent growth inhibition in plant and animal pathogens

Bacterial competition drives the evolution of antibacterial mechanisms, yet how new activities arise remains poorly understood. A major route to innovation is the reuse of pre-existing genetic systems, whereby conserved protein modules are repurposed in new biological contexts to generate new capabilities. Here, we show that the ParB-CTPase fold, a conserved nucleotide-binding module best known for its role in chromosome segregation, can be functionally repurposed as an antibacterial toxin. We identify ToxB, a ParB-like domain embedded within the polymorphic toxin region of contact-dependent inhibition systems and show that it functions as a potent antibacterial effector. Structural and biochemical analyses reveal that ToxB retains the core architecture of the ParB-CTPase fold but lacks DNA-binding capability and preferentially binds ATP. This shift in nucleotide specificity underpins a distinct mode of action, in which ATP binding and hydrolysis trigger rapid nucleoid compaction, chromosome segregation defects, oxidative stress, cell chaining, and ultimately cell lysis. ToxB also exhibits toxic activity in plant cells, suggesting that it targets conserved cellular processes. Together, these findings provide direct experimental evidence that the ParB-NTPase fold is biologically versatile and can be repurposed for biological roles fundamentally distinct from its ancestral function in DNA segregation. ### Competing Interest Statement The authors have declared no competing interest. Wellcome Trust, https://ror.org/029chgv08, 221776/Z/2/Z, 227755/Z/23/Z Biotechnology and Biological Sciences Research Council, https://ror.org/00cwqg982, BB/X01097X/1 Diamond Light Source, MX32728

biorxiv.org