Diversity and Universality of Endosymbiotic in the Fish Parasite .

Although the presence of endosymbiotic rickettsial bacteria, specifically Megaira, has been reported in diverse habitats and a wide range of eukaryotic hosts, it remains unclear how broadly Megaira are distributed in a single host species. In this study we seek to address whether Megaira are present in most, if not all isolates, of the parasitic ciliate . Conserved regions of bacterial 16S rRNA genes were either PCR amplified, or assembled from deep sequencing data, from 18 isolates/populations of sampled worldwide (Brazil, Taiwan, and USA). We found that rickettsial rRNA sequences belonging to three out of four Megaira subclades could be consistently detected in all samples. collected from local fish farms tend to be inhabited by the same subclade of Megaira, whereas those derived from pet fish are often inhabited by more than one subclade of Megaira. Distributions of Megaira in thus better reflect the travel history, but not the phylogeny, of . In summary, our results suggest that may be dependent on this endosymbiotic relationship, and the association between Megaira and is more diverse than previously thought.