Parasitic wasps prey on flies, aphids, and butterflies by laying eggs inside their larvae. Upon hatching, the wasps kill the insects they infect. As such, if flies want to survive long enough to grow up and mate, they have to find ways to avoid being killed by these wasps. For several years, researchers have known that flies infected by a bacterium called Spiroplasma are less likely to die from wasp parasitism; however, the exact mechanism of this protection is unknown.
The Perlman lab at the University of Victoria have recently shown that Spiroplasma makes proteins called RIPs — or Ribosome Inactivating Proteins. You’ve maybe heard of another RIP before: Ricin. Ricin is made from castor oil plants, and was used by the Bulgarian secret police to assassinate Georgi Markov in the 1970s. This toxin was also featured in the hit AMC television show Breaking Bad. RIPs are highly toxic because they irreversibly damage cellular protein-making factories known as ribosomes, which are crucial for survival.
In their latest publication, the Perlman lab provides proof that these RIPs damage parasitic wasps without hurting the infected flies. This is an example of a symbiotic relationship. Flies give bacteria a place to live and nutrients to survive, and in return the bacteria protect flies from their natural predators by making toxic RIPs.
Summary written by: Lucas Jarche
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Generality of toxins in defensive symbiosis: Ribosome-inactivating proteins and defense against parasitic wasps in Drosophila