Midichloria

"Candidatus Midichloria" is a candidatus genus of Gram-negative, non-endospore-forming bacteria, with a bacillus shape around 0.45 μm in diameter and 1.2 μm in length. First described in 2004 with the temporary name IricES1, "Candidatus Midichloria" species are symbionts of several species of hard ticks (e.g., Ixodes ricinus and Ixodes uriae of the Ixodidae family).^[1] They live in the cells of the ovary of the females of this tick species. These bacteria have been observed in the mitochondria of the host cells, a trait that has never been described in any other symbiont of animals.

"Candidatus Midichloria" bacteria seem to consume the mitochondria they parasitize, possibly using them as a source of energy and/or molecules to multiply. The interaction of these symbionts with their host is currently unknown, though the 100% prevalence in the females of the host tick suggests a mutualistic association.^[2] Although there is no evidence that even up to 20 bacteria residing within the host cell mitochondria produce deleterious effects in Rhipicephalus bursi, the prevalence in R. bursi was estimated at 33% in females and 14% in males, suggesting that the relationship may be more complicated than previously thought.^[1] In I. ricinus, between 10 and 20 bacteria are known to produce deleterious effects, leading to the conclusion that "Candidatus Midichloria" consume mitochondria.^[3]