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Beewolves Protect Larvae with Antibiotic Cocktail from Symbionts

Digger wasps that typically hunt bees to feed their larvae are called “beewolves,” and they are known to house beneficial bacteria on their cocoons that guarantee protection against harmful microorganisms. A team of scientists from Germany has now discovered that symbiotic bacteria of the genus Streptomyces produce a cocktail of nine different antibiotics that protect the beewolf larvae from invading pathogens. Using imaging techniques based on mass spectrometry, the antibiotics could be displayed in vivo on the cocoon's exterior surface. Moreover, it was shown that the complementary actions of the nine symbiont-produced antibiotics confer a potent antimicrobial defense for the wasp larvae against a multitude of different pathogenic microorganisms. Thus, the scientists said, beewolves have, for millions of years, been taking advantage of a principle in human medicine that is known as “combination prophylaxis.” Many insects spend a part of their life underground and are exposed to the risk of fungal or bacterial infections. This is also the case for many digger wasp species that construct underground nests. Unlike bees that use pollen and nectar as food to nurture their larvae, digger wasps hunt insects to feed their offspring. Because of the warm and humid conditions, as well as the large amounts of organic material in their subterranean nests, both their food supply and their larvae are endangered by pathogens. Mold and bacterial infection are major threats and can cause larval death in many cases. Beewolves have evolved an elegant solution to the problem of fungal and bacterial infection. Earlier studies had shown that beewolves form a symbiotic relationship with bacteria of the genus Streptomyces. Female beewolves cultivate these bacteria in specialized antennal gland reservoirs and apply them to the ceiling of the brood cells. Beewolf larvae later take up the bacteria and transfer the symbionts actively to their cocoons, thereby increasing their survival probability.

However, until the current discovery of the nine symbiont-produced antibiotics that, in combination, have a broad-based anti-pathogen activity, it has been unclear how this protection is achieved.

"Astonishingly, little is known about the ecological importance of antibiotics in their natural environment. Supported by mass spectrometric imaging we are now able to better understand the natural role of antibiotic substances in the environment," said Dr. Aleš Svatoš, the senior author of the study.

The scientists believe that imaging techniques can help to provide important insights, especially into the exploration of symbiotic interactions.

"We suppose that protective symbioses like the ones between beewolves and Streptomyces bacteria are much more common in the animal kingdom than previously assumed," said Dr. Martin Kaltenpoth, an author of the study. "An analysis of the substances involved not only contributes to the understanding of the evolution of such symbioses, but could also lead to the discovery of interesting new drug candidates for human medicine."

This research was reported online on February 28, 2010, in Nature Chemical Biology. [Press release] [Nature Chemical Biology abstract]