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“Candidatus Hafkinia simulans” gen. nov., sp. nov., a Novel Holospora-Like Bacterium from the Macronucleus of the Rare Brackish Water Ciliate Frontonia salmastra (Oligohymenophorea, Ciliophora): Multidisciplinary Characterization of the New Endosymbiont and Its Host

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Abstract

We characterized a novel Holospora-like bacterium (HLB) (Alphaproteobacteria, Holosporales) living in the macronucleus of the brackish water ciliate Frontonia salmastra. This bacterium was morphologically and ultrastructurally investigated, and its life cycle and infection capabilities were described. We also obtained its 16S rRNA gene sequence and performed in situ hybridization experiments with a specifically-designed probe. A new taxon, “Candidatus Hafkinia simulans”, was established for this HLB. The phylogeny of the family Holosporaceae based on 16S rRNA gene sequences was inferred, adding to the already available data both the sequence of the novel bacterium and those of other Holospora and HLB species recently characterized. Our phylogenetic analysis provided molecular support for the monophyly of HLBs and placed the new endosymbiont as the sister genus of Holospora. Additionally, the host ciliate F. salmastra, recorded in Europe for the first time, was concurrently described through a multidisciplinary study. Frontonia salmastra’s phylogenetic position in the subclass Peniculia and the genus Frontonia was assessed according to 18S rRNA gene sequencing. Comments on the biodiversity of this genus were added according to past and recent literature.

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Acknowledgments

The authors are grateful to Simone Gabrielli for his patient and precious assistance in tree editing.

Funding

This research was supported by a grant from Italian Research Ministry (MIUR – Ministero Italiano dell’ Università e della Ricerca) to S.I. Fokin; and by the PRA_2018_63 project from University of Pisa to G. Petroni.

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Authors and Affiliations

  1. Department of Biology, University of Pisa, 56126, Pisa, Italy

    Sergei I. Fokin, Valentina Serra, Filippo Ferrantini, Letizia Modeo & Giulio Petroni

  2. Department of Invertebrate Zoology, St. Petersburg State University, St. Petersburg, Russia, 199034

    Sergei I. Fokin

  3. St. Petersburg Branch of the S.I. Vavilov Institute of History of Science and Technology, Russian Academy of Sciences, St. Petersburg, Russia, 199034

    Sergei I. Fokin

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  1. Sergei I. Fokin
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  2. Valentina Serra
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  3. Filippo Ferrantini
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  4. Letizia Modeo
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Correspondence to Sergei I. Fokin or Valentina Serra.

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Fokin, S.I., Serra, V., Ferrantini, F. et al. “Candidatus Hafkinia simulans” gen. nov., sp. nov., a Novel Holospora-Like Bacterium from the Macronucleus of the Rare Brackish Water Ciliate Frontonia salmastra (Oligohymenophorea, Ciliophora): Multidisciplinary Characterization of the New Endosymbiont and Its Host. Microb Ecol 77, 1092–1106 (2019). https://doi.org/10.1007/s00248-018-1311-0

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  • DOI: https://doi.org/10.1007/s00248-018-1311-0

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  1. Giulio Petroni View author profile