They are notorious among nature lovers: As is well known, ticks can transmit dangerous bacteria to us. But as researchers are now reporting, the reverse is also true: the bloodsuckers have to protect themselves from the skin bacteria of their victims. To do this, they once “stole” a gene that enables them to produce an antibiotic. According to the study, this way they put an end to the staphylococcus species that are harmless to us and that they ingest with their blood meal. Unfortunately, however, the substance does not work against the Lyme disease bacteria in the ticks, which they can therefore transmit to us, the scientists report.
We like to meet butterflies, ladybugs and the like, but it is well known that nature also includes some animals that we don’t like to deal with: the tick is a prime example of this. The parasites don’t just target our blood – the species that are widespread in Europe and North America can transmit Lyme borreliosis, a disease caused by bacteria. This aspect is usually the focus of public attention as well as science.
But the researchers led by Seemay Chou from the University of California in San Francisco have been studying the ticks for several years from a different perspective: They are devoting themselves to the question of how the bloodsuckers protect themselves from becoming infected with potential pathogens from their victims. In previous investigations, they came across a gene in the genome of the tick species Ixodes scapularis that produces a protein that kills microbes. In the current study, they have now examined more closely what this gene called dae2 is all about.
A stolen gene
Their genetic analyzes uncovered the interesting history of this genetic make-up: Comparisons showed that this dae2 gene did not originally come from the tick, but was “stolen”. It originally developed in bacteria that use the substance encoded by this gene as a weapon against other microbes. Certain genetic traits show that the ancestors of the ticks took over the gene into their genetic make-up several hundred million years ago – presumably at the time when they began to feed on blood. It was therefore an interesting case of what is known as horizontal gene transfer – from a bacterium to an animal, say the researchers.
But which pathogens does the antibiotic produced by dae2 protect the parasites from? The scientists investigated this question by testing various types of bacteria. It turned out that the active ingredient is apparently directed against Staphylococcus bacteria, some species of which are often found on the skin of mammals, including humans. These are usually so-called commensals – microbes that peacefully coexist with us. “After we put the Dae2 protein in a vial with a culture liquid that was clouded by staph bacteria, the question was literally cleared up,” says Chou. The active ingredient kills these microbes very quickly.
Refined equipment
In order to investigate how important this effect is for the health of the ticks, the researchers carried out analyzes on the bloodsuckers. It was found that the protein is produced in their digestive system and saliva. Apparently it destroys the microbes harmful to the parasites when the blood is absorbed. How important this is became clear when the scientists switched off the gene or the product in some test ticks: In contrast to comparison animals, they showed developmental disorders.
As further studies have shown, the pathogens of Lyme borreliosis are not killed by the tick antibiotic. But that is not necessary either, say the scientists, because it is known that these bacteria do not harm the bloodsuckers. “It doesn’t make sense for ticks to kill bacteria that are known to coexist with no problems,” says Chou. For us, however, this aspect becomes a considerable health risk. “The results change the way ticks interact with microbes. Microbes that are transmitted by ticks cause diseases in humans and animals all over the world, but that’s only half the story: The commensals of the parasites become pathogens in us and ours can in turn cause problems for the ticks, ”the scientist sums up.
Quelle: University of California in San Francisco, Cell Press, Fachartikel: Cell, doi: 10.1016/j.cell.2020.10.042
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