Mysterious protein sets up a beneficial partnership between bacteria and insects

Buchnera bacteria that live in the cells of insects known as aphids secrete a protein called SyeA, which is crucial for colonization. The structural similarity of SyeA to proteins secreted by disease-causing bacteria indicates that the beneficial symbiotic relationship between Buchnera and aphids had pathogenic origins. Symbiotic bacteria colonize aphid hosts by secreting a protein similar to some used by pathogens.