RESEARCH ARTICLE Ixodes ricinus and Its Endosymbiont Midichloria mitochondrii: A Comparative Proteomic Analysis of Salivary Glands and Ovaries

Hard ticks are hematophagous arthropods that act as vectors of numerous pathogenic microorganisms of high relevance in human and veterinary medicine. Ixodes ricinus is one of the most important tick species in Europe, due to its role of vector of pathogenic bacteria such as Borrelia burgdorferi and Anaplasma phagocytophilum, of viruses such as tick borne encephalitis virus and of protozoans as Babesia spp. In addition to these pathogens, I. ricinus harbors a symbiotic bacterium,Midichloria mitochondrii. This is the dominant bac-teria associated to I. ricinus, but its biological role is not yet understood. MostM.mitochon-drii symbionts are localized in the tick ovaries, and they are transmitted to the progeny.M. mitochondrii bacteria have however also been detected in the salivary glands and saliva of I. ricinus, as well as in the blood of vertebrate hosts of the tick, prompting the hypothesis of an infectious role of this bacterium. To investigate, from a proteomic point of view, the tick I. ricinus and its symbiont, we generated the protein profile of the ovary tissue (OT) and of sali-vary glands (SG) of adult females of this tick species. To compare the OT and SG profiles, 2-DE profiling followed by LC-MS/MS protein identification were performed. We detected 2