Content: Myxobacteria engage in a social behavior where they transiently fuse their outer membranes (OM) and exchange lipids and proteins between cells.This process is robust as large quantities of OM material is transferred, which can allow phenotypic rescue in strains that contain genetic lesions for the production of OM components.This intimate behavior is regulated by a polymorphic cell surface receptor called TraA, which mediates self-recognition, and is postulated to catalyze OM fusion.