This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: When you think of viruses, you probably think of flu-like symptoms and quarantines. Humankind has suffered from viral diseases ranging from smallpox to COVID-19, hantavirus and Ebola since the dawn of recorded history.
However, humans are not the only living organisms susceptible to viral infections. In fact, the greatest number and most diverse collection of viruses are those that infect bacteria. Amazingly, some bacteria have transformed these infectious invaders into gene transfer agents (GTAs) that help them exchange genetic material among themselves.
This process is a type of horizontal gene transfer that allows genetic information to be shared among related bacteria rather than being restricted to inheritance by the offspring of a parent cell. Because GTAs can empower bacteria to acquire new traits and spread disease-related genes, studying them may help unlock important applications in human health and biotechnology, including those that combat the spread of antibiotic resistance. A recent study in Nature Microbiology, for example, pinpointed a cluster of genes that trigger bacteria to release GTA particles that can spread antibiotic-resistance genes.
In 2000, we isolated GTA genes from the bacterium Rhodobacter capsulatus and analyzed the proteins that these genes instruct the cells to make. We discovered that the proteins were very similar in structure to those found in a class of viruses known as tailed phages. This was the first evidence that a gene transfer agent bears more than just a passing resemblance to a virus.
Subsequent studies showed that others are also derived from ancient viruses. Since then, GTA genes have been discovered in a wide variety of bacteria, including the infectious agents responsible for cat-scratch fever and typhus, and abundant marine organisms. A small, random sample of genes from the bacterium is packaged into a geometrically shaped protein structure that forms the head of a gene transfer agent, while other proteins form a tube-like tail.
The image below shows the R. capsulatus gene transfer agent as it appears in an electron microscope (on the left) and its cryogenic-electron tomographic structure, displayed using the ChimeraX visualization program (on the right). After release from the bacterium, flexible proteins that decorate the GTA bind to and anchor it to the surface of a target cell. Then, the genetic material contained within the head of the GTA is transferred through the tail and into the target cell, with help from bacterial proteins located in the cell membrane.
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