Heckmann and Schmidt described the genus for bacterial endosymbionts of freshwater ciliates affiliated with the genus , and the species for obligate endosymbionts living in the cytoplasm of . Pure cultures of the type strain could not be established due to the obligate nature of the symbiotic relationship between the endosymbionts and their hosts. Therefore, is one of a few bacterial species with validly published names that lack a deposited pure culture. Meanwhile, it was demonstrated that the endosymbionts used for the description of the type of are closely related to obligately free-living strains. Similarity values of the 16S rRNA gene sequences obtained from the endosymbionts in the ciliate culture and free-living isolates in the range 99.1–99.4 % indicate that these organisms belong to the same species. Here, we have emended the description of by characterization of free-living strains maintained as pure cultures. The species was characterized as having low G+C contents of the DNA (44–46 mol%), small genome sizes (1.5–2.5 Mbp) and a lack of motility. Because of distinct differences in lifestyle and the genome size of strains, we propose that two novel subspecies should be established, subsp. subsp. nov. [with a type, which is a description based on endosymbionts in the culture ‘stock 15’ of the ciliate (ATCC 30859)] and subsp. subsp. nov. [with the type strain QLW-P1DMWA-1 (=DSM 18221=CIP 109841)], for the obligate endosymbionts of and and obligately free-living strains, respectively.


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Images of colonies formed by a pure culture of a free-lining strain. [PDF](52 KB)


Graph showing the maximum optical density in NSY medium of the strains described, related free-living strains and the type strains of four other species affiliated with the family . [PDF](36 KB)


Habitats from which the free-living strains investigated were isolated. [PDF](54 KB)

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