Science1 publisher2 min readPublished
A gene cluster triggers the phage-derived particles that carry resistance genes between bacteria
Some bacteria build particles from domesticated virus parts and die to release them, handing pieces of their own genome to relatives. Antibiotic resistance genes can ride along, and a gene cluster controls the switch.
The Scientist · Science desk
What happened
- A study in Nature Microbiology has pinpointed a cluster of genes that trigger bacteria to release gene transfer agent particles, and those particles can carry antibiotic-resistance genes into other cells.
- Each particle holds a small, random sample of the producing cell's genes inside a geometric protein head, with other proteins forming the tube-like tail that delivers the DNA.
- Releasing the particles kills the producer, which bursts, and most of a population survives because only a small subset of cells are allowed to switch the production genes on.
- GTA genes have since been found across many bacteria, including the infectious agents responsible for cat-scratch fever and typhus, and abundant marine organisms.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- capability A trigger encoded in a chromosomal gene cluster can be searched for in sequence data and, in principle, blocked at induction. That is a different kind of intervention point from anything aimed at a free-floating element.
- constraint The machinery exists. Because the cargo is a random draw from the producer's genome, the importance of this route is an empirical question about how often the right gene gets packaged.
- exposure Species that infect people already carry the genes for this machinery, so the route reaches beyond the laboratory strain in which resistance transfer was first demonstrated.
Whether this route moves much antibiotic resistance in a real population depends on how often a resistance gene ends up inside a head, and on how many particles a bursting cell releases. Packaging is random, so the rate is hard to pin down. The phys.org account gives no numbers for either, and no comparison with plasmids or other transfer routes [19].
Flexible proteins that decorate the particle's outside anchor it to the surface of a target cell, and the DNA in the head then travels through the tail into that cell, helped by bacterial proteins sitting in the membrane [8]. Inside, other proteins bind the incoming DNA and insert it into the host genome [9]. The exchange is a form of horizontal gene transfer, and the account describes it as sharing among related bacteria [2].
Two conditions make the sacrifice worthwhile, according to the authors. One is running out of nutrients, amino acids in particular, where new gene combinations might let a cell reach nutrients it cannot currently use [12]. The other is a chemical signal from neighbouring cells telling it that many related target cells are close by [13].
Researchers isolated the gene transfer agent genes of Rhodobacter capsulatus in 2000 and found that the proteins built from them closely resemble tailed phage proteins [4]; later studies found other gene transfer agents also descend from ancient viruses [5]. The Nature Microbiology gene cluster comes 26 years after that first structural result [16]. The phys.org piece is written in the first person by researchers who did the 2000 work [15].
The cluster sits in the chromosome, so it can be searched for in sequence data and, in principle, blocked at the point of induction [3]. The stronger claim, that resistance surveillance is looking at the wrong route, needs more than this evidence: the earliest laboratory demonstration of a gene transfer agent moved antibiotic resistance in R. capsulatus [14], and the authors write that more remains to be discovered before horizontal gene transfer can be put to real-world use [18]. I would look for the cluster in pathogen genomes; its share of resistance spread is not measured yet.
What to watch
- A measured rate: particles released per lysed cell, and how often a given resistance gene is packaged into a head.
- Whether the Nature Microbiology gene cluster is present and inducible in the pathogens listed as carrying GTA genes, including the agents of cat-scratch fever and typhus.
- Whether interfering with either trigger, amino acid starvation or the neighbour-sensing signal, suppresses particle release in culture.