Prevalence of Cardinium Bacteria in Planthoppers and Spider Mites and Taxonomic Revision of “ Candidatus Cardinium hertigii” Based on Detection of a New Cardinium Group from Biting Midges

Cardinium bacteria, members of the phylumCytophaga -Flavobacterium -Bacteroides (CFB), are intracellular bacteria in arthropods that are capable of inducing reproductive abnormalities in their hosts, which include parasitic wasps, mites, and spiders. A high frequency ofCardinium infection was detected in planthoppers (27 out of 57 species were infected). A high frequency ofCardinium infection was also found in spider mites (9 out of 22 species were infected). Frequencies of double infection byCardinium andWolbachia bacteria (Alphaproteobacteria capable of manipulating reproduction of their hosts) were disproportionately high in planthoppers but not in spider mites. A new group of bacteria, phylogenetically closely related to but distinct from previously describedCardinium bacteria (based on 16S rRNA andgyrB genes) was found in 4 out of 25 species ofCulicoides biting midges. These bacteria possessed a microfilament-like structure that is a morphological feature previously found inCardinium andPaenicardinium . The bacteria close to the genusCardinium consist of at least three groups, A, B, and C. Group A is present in various species of arthropods and was previously referred to as “Candidatus Cardinium hertigii,” group B is present in plant parasitic nematodes and was previously referred to as “Candidatus Paenicardinium endonii,” and group C is present inCulicoides biting midges. On the basis of morphological and molecular data, we propose that the nomenclature of these three groups be integrated into a single species, “Candidatus Cardinium hertigii.”