Mitobiosis: The intra-mitochondrial bacterial symbiosis in Ixodes ticks

Arthropods, a highly diverse and abundant group of organisms, showcase a remarkable spectrum of symbiotic mechanisms, making them a fascinating subject in studying biological interactions. Through these intricate symbioses, arthropods have been endowed with an array of significant biological activities, including enhanced reproductive fitness.
Ticks are far from being solitary; apart from horizontally acquired microbes (: pathogens), they carry endosymbiotic bacteria, which are inherited vertically and passed from one generation to the next. Midichloria mitochondrii is endosymbiotic bacterium of Ixodes ticks and is unique in its capacity to invade mitochondria. The Array tomography and 3D reconstruction determines that the symbiont occupies the intermembrane space of mitochondria.
Limited experimental options were available for studying Midichloria biology, but our technological progress, which includes generating symbiont-free I. ricinus ticks has breached the previous limits. We have shown that symbiont-free tick females display poor fitness with compromised energetics. Using our comparative system of symbiont-free and wild-type ticks, we determined molecular changes inherent to intra-mitochondrial symbiosis at multiple levels of molecular hierarchy: metabolomics, transcriptomics, and proteomics.
While the symbiont has a positive effect on a hosting ticks, the symbiont needs to be hold at bay to prevent overpopulating tick organs. Using RNAi-mediated silencing, components of Toll pathway or STING regulation were evaluated for the role in curbing symbiotic loads.
Exploiting our model to shed more light on molecular and cellular mechanisms underlying the unique relationship between mitochondria and bacteria may bring novel concepts of endosymbiosis between bacteria and eukaryotic organelles.