How ticks can live on blood alone

Symbiosis partner supplies bloodsuckers with essential vitamins

Ticks feed exclusively on blood - and therefore would actually have to suffer from vitamin deficiencies. © Ixodes / thinkstock
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Microbial helper: Ticks feed on blood alone - and should therefore actually be destroyed by a vitamin deficiency. Researchers have now discovered why this is not the case. Accordingly, a bacterium supplies the bloodsucker with vital B vitamins. The germ lives in symbiosis with the ticks and makes their one-sided diet possible in the first place.

Warm weather and summery temperatures are not only luring us out - ticks are also increasingly active. The small pest spirits lurk on grasses and bushes on their human and animal victims, on whose blood they feed. Unlike, for example, mosquitoes, the animals feed exclusively on the red body fluid. Each of their meals is a blood meal.

This highly specialized diet has one major drawback: it is low in vitamins from the B complex. Ticks are actually dependent on these nutrients. They need them to survive. So how do the tiny animals cover their vitamin needs, if not their diet? Scientists have long had a guess: Could it be that a symbiotic partner supplies the animals with the missing substances - for example, a bacterium?

Bacterium as a vitamin supplier

To test this, Olivier Duron of the University of Montpellier and his colleagues have now gone in search of microbial roommates in the body of the tick. In studies with ticks of the model Ornithodoros moubata they noticed: The hosted by the microbial community is dominated by a certain Gram-negative strain of bacteria from the genus Francisella conspicuously - in all stages of development. So the researchers found the germ in both larvae, as well as nymphs and adult ticks.

Colonies of bacteria of the genus Francisella © CDC

The suspicion was therefore obvious that this bacterium could play a crucial role in the development and survival of the bloodsuckers. In fact, a subsequent analysis of the bacterial genome showed that the microbe can synthesize vitamin B8, vitamin B2 and vitamin B9 - scientists are talking about biotin, riboflavin and folic acid. display

Inhibited development

But does the microbe really provide these nutrients to the ticks? The researchers tested this by removing the bacterium from the body of growing ticks. It turned out: The young ticks ceased their development. If they got the vitamins that the germ produced, but were given as nutritional supplements, they then continued to grow normally.

According to the team, this is the deciding factor: only the symbiotic partnership with the Francisella bacterium will allow the bloodsuckers to meet and grow and thrive on their vitamin B needs. In the course of its evolution, the germ has lost about half of its protein-coding genetic sequences - but the vitamin B synthesis pathways were retained, as further analyzes revealed. "This confirms the importance of these genes in developing their partnership with the ticks, " write Duron and his colleagues.

The only symbiosis partner?

With this, the scientists have finally clarified why the bloodsuckers can feed themselves so one-sidedly. However, the Francisella bacterium may not be the only symbiotic partner that the ticks rely on when it comes to nutrients. Another candidate is according to the team a microbe from the genus Coxiella.

Although this symbiotic bacterium is only distantly related to Francisella. Studies show, however, that the germ can also synthesize B vitamins and the fitness of some types of ticks suffers when it is eliminated using antibiotics. (Current Biology, 2018; doi: 10.1016 / j.cub.2018.04.038)

(CNRS / Current Biology, 01.06.2018 - DAL)