Evolution mystery: Spider venom and bacteria share same toxin
It's a case of evolutionary detective work. Biology researchers at Lewis & Clark College and the University of Arizona have found evidence for an ancient transfer of a toxin between ancestors of two very dissimilar organisms-spiders and a bacterium. But the mystery remains as how the toxin passed between the two organisms. Their research is published this month in the journal Bioinformatics, 22(3): 264-268, in an article titled "Lateral gene transfer of a dermonecrotic toxin between spiders and bacteria."

"We are piecing together an historical puzzle with evidence from living descendants of an ancient ancestor," said Greta Binford, assistant professor of biology at Lewis & Clark. Her coresearcher on the project is Matthew Cordes, assistant professor of biochemistry and molecular biophysics at the University of Arizona. The toxin is uniquely found in the venom cocktail of brown or violin spiders, including the brown recluse, and in some Corynebacteria. The toxin from the spider's venom can kill flesh at the bite site; the bacterium causes various illnesses in farm animals.

"Our research was inspired by the fact that we have a group of spiders with a unique toxin, and that toxin also happens to exist outside the animal kingdom in this particular bacterium," she added. "A pattern like this raises the possibility of lateral gene transfer as a explanation." Lateral gene transfer refers to the movement of genes between the genomes of unrelated organisms. This contrasts with vertical transfer of genes from parent to offspring.

Cordes and Binford found a common structural motif at the end of both toxic proteins that is not found in any other proteins. Evidence for common ancestry (homology) of the toxins had previously been noted, but this uniquely shared structural bit is best explained by these toxins being more