When a Virus Saves Bacteria From Suicide
In nature : The main enemies of bacteria are not antibiotics, but bacteriophages (or phages). Ten times more than bacteria, they only attack them. As can be seen from the above photos taken with a microscope, phages most of the time have a mushroom shape: the head contains the genetic material of the virus, which is injected into the bacterium by the foot. As recently explained in the World Science & Techno Supplement ( available here ), when they meet their prey,”The phages infect them and multiply using the material of their host. Then they destroy the wall of the bacteria to free themselves, ready to attack new bacteria. A complete cycle takes place very quickly, from a few minutes to an hour. “
Under constant pressure : phages, bacteria have developed many defense strategies. Some have made changes to their surface to block entry to viruses. Other bacteria attack the genetic material of viruses and prevent it from running the replication program. But probably the most fascinating strategy is that of hara-kiri. In some species, the infected bacteria will commit suicide by poisoning themselves. Specifically, it has at its disposal a toxin-antitoxin system: it manufactures both a poison and an antidote that neutralizes it. When attacked by a virus, the bacteria “release” the toxin and die. This gesture is considered “altruistic” by biologists because if it leads to the death of the individual,
Bacteria: are not the only ones to evolve. In what looks like an arms race, viruses do not stay inactive. Thus, a team of British and New Zealand researchers just published in October, in the journal PLoS Genetics , a study showing the incredible parade to the technique of hara-kiri found a virus called ΦTE. The bacterium it infects is called Pectobacterium atrosepticum. It is a pathogen for many plants and it causes the black leg , a disease of the potato. Having noticed that some specimens of ΦTE managed to break out of Pectobacterium atrosepticumafter having infected it, the authors of the article went to see it more closely. And they realized that these mutant phages synthesized a very successful imitation of the antidote, which prevented the toxin from acting. The bacterium was saved from suicide but, of course, this rescue did not arrange its business since it was only temporary: the goal of the maneuver was to keep the bacterium alive for the time that it multiplies and then leave for the assault of the colony.
As one of the authors of the study, George Salmond (Cambridge University) explains , “this work sheds light on the incredibly dynamic world of co-evolution between bacteria and their viruses.” In the course of their research, biologists also realized that, not content to thwart the “suicidal” strategy of bacteria, phages were able to do even better. Researchers have found that some viruses can take the DNA encoding the toxin-antitoxin defense system and transplant it to other hosts in the genetic material of their prey. History to teach them to defend against … competing viruses of ΦTE, what biologists have called an “altruistic infection”. It will not be the first time in history that a protagonist arms his best opponent against another enemy …