Borrelia burgdorferi chemotaxis toward tick protein Salp12 contributes to acquisition

Lyme disease is a common tick-borne infection caused by the spirochete Borrelia burgdorferi sensu stricto (s.s.). B. burgdorferi s.s. may utilize chemotaxis, the directional migration towards or away from a chemical stimulus, for transmission, acquisition, and infection. However, the specific signals recognized by the spirochete for these events have not been defined. In this study, we identify an Ixodes scapularis salivary gland protein, Salp12, that is a chemoattractant for the spirochete. We demonstrate that Salp12 is expressed in the I. scapularis salivary glands and midgut and expression is not impacted by B. burgdorferi s.s. infection. Knockdown of Salp12 in the salivary glands or passive immunization against Salp12 reduces acquisition of the spirochete by ticks but acquisition is not completely prevented. Knockdown does not impact transmission of B. burgdorferi s.s. This work suggests a new role for chemotaxis in acquisition of the spirochete and suggests that recognition of Salp12 contributes to this phenomenon.