MIDICHLORIA MITOCHONDRII AS AN EMERGING INFECTIOUS AGENT: MOLECULAR AND IMMUNOLOGICAL STUDIES ON THE INTRA-MITOCHONDRIAL SYMBIONT OF THE HARD TICK IXODES RICINUS

M. mitochondrii is an alpha proteobacteria belonging to the order Rickettsiales. It is an intracellular bacterium present in different tick species and in particular it is studied in the hard tick I. ricinus. The prevalence of M. mitochondrii in I. ricinus is 100% in females and around 40% in males. The recently sequenced genome of M. mitochondrii revealed the presence of 26 putative flagellar genes. Open questions are whether these genes are expressed and whether they possess the domains expected for the flagellar function. To answer to these questions, a putative flagellar protein has been produced in recombinant form, purified and used for the production of polyclonal antibodies. These were used for immunostainig and immunogold detection of M. mitochondrii in I. ricinus ovary. Furthermore, the expression of seven flagellar genes has been evaluated and the proteins codified by the 26 genes have been analyzed for the presence of domains specific for flagellar proteins. In I. ricinus, M. mitochondrii is observed in the oocytes and in other cells of the ovary, where the symbiont is present in the cell cytoplasm and inside the mitochondria. No studies have so far investigated whether M. mitochondrii is present in the salivary glands of the tick and whether it is transmitted to vertebrates during the tick blood meal. To address the above questions, we used a recombinant antigen of M. mitochondrii (to screen vertebrate sera) and antibodies against this antigen (for the staining of the symbiont in the salivary glands). In conclusion, the obtained results provide evidences that: 1) M. mitochondrii is the first rickettsiales that posses a flagellar structure; 2) M. mitochondrii, detected in the salivary glands of I. ricinus, could be transmitted to the vertebrate host during the tick bite; 3) vertebrate hosts develop an antigenic response against a recombinant protein of M. mitochondrii suggesting the possibility that M. mitochondrii is infectious to vertebrates.