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Front Microbiol. 2017 Feb 9;8:189. doi: 10.3389/fmicb.2017.00189. eCollection 2017.

Diversity and Universality of Endosymbiotic Rickettsia in the Fish Parasite Ichthyophthirius multifiliis.

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Department of Biology, Hamilton College, Clinton NY, USA.
Department of Biology, Indiana University, BloomingtonIN, USA; National Center for Genome Analysis Support, Indiana University, BloomingtonIN, USA.
Department of Aquatic Biosciences, National Chyai University Chyai City, Taiwan.
Departamento de Aquicultura, Centro de Ciências Agrárias, Universidade Federal de Santa Catarina Florianópolis, Brazil.
Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca NY, USA.
Institute of Molecular Biology, Academia Sinica Taipei, Taiwan.
Department of Biology, Hamilton College, ClintonNY, USA; Institute of Molecular Biology, Academia SinicaTaipei, Taiwan.


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


Ciliophora; Sphingobacteria; alphaproteobacteria; hyperparasitism; phagocytosis; symbiosis

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