Cardinium

""Candidatus" Cardinium" is a genus of Gram-negative parasitic bacteria that reside within cells of some arthropods and nematodes. Although they have not yet been isolated in pure culture (hence the designation "Candidatus"), they are known to negatively influence reproduction in their hosts in order to further their own proliferation. This leads to their classification as a reproductive parasite. One of the only other examples of this type of parasitism is the genus "Wolbachia", which also infects arthropods. These two genera can also co-infect the same animal, as in some nematodes. ""Candidatus" Cardinium" bacteria use many of the same methods to interfere with host reproduction as "Wolbachia," including inducing cytoplasmic incompatibility and distorting the sex ratio in the host population to favor females. The mechanisms by which ""Candidatus" Cardinium" induces these conditions in hosts are thought to be different from the mechanisms used by "Wolbachia". ""Candidatus" Cardinium" bacteria are maternally inherited; infections are maintained through generations through the egg cells (termed vertical transmission). It is estimated that 6-10% of all arthropods are infected with "Cardinium" bacteria.
""Candidatus" Cardinium" were first discovered in 1996 in the cells of deer ticks, although attempts to culture them independently of host cells were unsuccessful.