Microbial Ecology

, Volume 61, Issue 2, pp 455–464 | Cite as

Detection of a Novel Subspecies of Francisella noatunensis as Endosymbiont of the Ciliate Euplotes raikovi

  • Martina Schrallhammer
  • Michael Schweikert
  • Adriana Vallesi
  • Franco Verni
  • Giulio Petroni
Microbiology of Aquatic Systems


Francisella are facultative intracellular bacteria causing severe disease in a broad range of animals. Two species are notable: Francisella tularensis, the causative organism of tularemia and a putative warfare agent, and Francisella noatunensis, an emerging fish pathogen causing significant losses in wild and farmed fish. Although various aspects of Francisella biology have been intensively studied, their natural reservoir in periods between massive outbreaks remains mysterious. Protists have been suspected to serve as a disguised vector of Francisella and co-culturing attempts demonstrate that some species are able to survive and multiply within protozoan cells. Here, we report the first finding of a natural occurrence of Francisella sp. as a protist endosymbiont. By molecular and morphological approaches, we identified intracellular bacteria localized in a strain of the marine ciliate Euplotes raikovi, isolated from the coast of Adriatic Sea. Phylogenetic analysis placed these endosymbionts within the genus Francisella, in close but distinct association with F. noatunensis. We suggest the establishment of a novel subspecies within F. noatunensis and propose the cytoplasmatic endosymbiont of E. raikovi as “Candidatus F. noatunensis subsp. endociliophora” subsp. nov.


Intracellular Bacterium Tularemia Francisella Tularensis Tularensis Subsp Host Cytoplasm 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



The authors wish to thank P. Luporini for providing the E. raikovi strain used in this study. M. Barresi is gratefully acknowledged for her technical assistance in many experiments, S. Gabrielli and S. Neumann for photographic artwork, and an anonymous reviewer for English editing. This work was supported by a PRIN fellowship (protocol 2008TRZSXF_002) from the Italian Research Ministry (MIUR).

Supplementary material

248_2010_9772_Fig5_ESM.gif (288 kb)
Figure S1

Fluorescence in situ hybridization of Euplotes raikovi; a) signal from probe EUB338; b) signal from probe FRANCIS1167 specific for Francisella; c) differential interference contrast. Scale bar = 20 μm. (GIF 288 kb)

248_2010_9772_MOESM1_ESM.tif (9 mb)
High resulotion image (TIFF 9179 kb)
248_2010_9772_Fig6_ESM.gif (25 kb)
Figure S2

Transmission electron micrograph of Euplotes raikovi cells, different section than that displayed in Fig. 3. Scale bar = 1 μm. (GIF 25 kb)

248_2010_9772_MOESM2_ESM.tif (1.3 mb)
High resulotion image (TIFF 1317 kb)


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Copyright information

© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  • Martina Schrallhammer
    • 1
    • 2
  • Michael Schweikert
    • 3
  • Adriana Vallesi
    • 4
  • Franco Verni
    • 1
  • Giulio Petroni
    • 1
  1. 1.Dipartimento di BiologiaUniversità di PisaPisaItaly
  2. 2.Institute of HydrobiologyDresden University of TechnologyDresdenGermany
  3. 3.Biologisches InstitutUniversität StuttgartStuttgartGermany
  4. 4.Dipartimento di Scienze Ambientali e NaturaliUniversità di CamerinoCamerinoItaly

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