Hyalomma marginatum has an unusual multi-partners nutritional system: B vitamin-provisioning is partitioned between an ancestral symbiont, Francisella, and a recently acquired bacterial partner, the intramitochondrial symbiont Midichloria. The Francisella genome underwent a massive genome reduction and has lost functionality of the biotin biosynthesis pathway yet essential for nutritional symbiosis. The co-infection with Midichloria prevents the collapse of nutritional Francisella endosymbiosis by compensating for biotin biosynthesis