Pederin is a highly bioactive natural product orignially thought to be produced by Paederus beetles as this compound can be extracted from these animals. In 2002, studying the beetle genome and the biosynthesis of this natural product the group of Jörn Piel at the Max Planck in Jena found that this highly toxic compound actually originates from bacteria (Pseudomonas sp.) which live endosymbiotically within the beetle (PNAS paper).
The obvious advantage for the beetle is that it becomes toxic to potential preditors and does not have to produce the toxin by itself. The bacteria do the job. In humans this beetle, also called blister beetle, causes strong dermatitis (see image).
Dermatitis from Paederus blister beetle (image from Dermatology Online Journal 12(7):9)
However, since pederin potently inhibits DNA synthesis and it is a blocker of cell division and leads to cell death and the compound can be detected in the haemolymph of the beetle the question is how does this insect protect itself from the toxic effect of the compound? Do Paederus beetles have an endogenous system (sink) to protect themselves from the molecular effects of pederin? Maybe, if we could understand how nature solves the problem we could develop a strategy to protect blister beetle dermatitis which is prevalent in many parts of the world. Interestingly, Paederus dermatitis in Africa is a relatively severe form of dermatitis. The better response to a combination of topical steroids and oral antibiotics may in fact indicate concurrent bacterial infection. Thus, maybe the endosymbiont Pseudomonas is transmitted from the beetle to the skin and continues to produce pederin, which then leads to the symptom of dermatitis, a hypothesis that has not beed addressed so far.