A Trojan horse pathogen breaking through partner-choice barriers in the insect gut.

gut symbiosis. This bacterium resembles symbionts by using wrapping motility to traverse the host's sorting organ, inducing symbiotic organ morphogenesis and colonizing it. Unlike mutualists, however, it resists host digestion for nutrient acquisition, breaches the gut epithelium, and causes sepsis, rapidly killing the host. Colonization of the symbiotic organ is essential for its lethality. This case shows how pathogens can exploit mutualisms, highlighting the evolutionary pressures shaping partner-choice mechanisms and the fragility of even highly specialized mutualisms.