Toroidal surface complexes of bacteriophage ϕ12 are responsible for host-cell attachment

► Subtomogram averaging reveals enhanced detail of a ϕ12 cystovirus surface protein complex. ► The surface protein complex has a toroidal shape and six-fold symmetry. ► It is encoded by the medium-size genome segment. ► The proteins of the surface complex most likely are one copy of P3a and three copies of P3c.