**6. Conclusions**

We have reported and characterized a novel species of *Holospora*-like bacteria, "*Ca*. Gortzia yakutica" sp. nov. These intracellular symbionts display several unique biological features such as a complex live cycle and two morphological forms, frequent specificity to the host species and localization inside the host cell, and a distinctive cell structure of infectious forms. Hence they are of interest to evolutionary and infection biology. HLB have been previously reported to be a monophyletic clade within order *Holosporales* based on based on phenotype features and molecular phylogeny. However, we demonstrate phylogenetic placement of genus *Preeria* is uncertain, probably due to the limitations of 16S rRNA-based analysis and the lack of described diversity in the genus currently comprised of only one species. Further research into these fascinating bacteria is well warranted for the understanding of the evolution and systems biology of nuclear endosymbionts.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1424-2818/12/5/198/ s1.

**Author Contributions:** Conceptualisation, A.Y.B., M.S.R., and M.S.G.; data curation, A.Y.B., A.V.P., and S.K.G.; Formal analysis, A.Y.B., A.V.P., and S.K.G.; Funding acquisition, M.S.G.; Investigation, A.Y.B., M.D.L., and S.Z.; Resources, M.S.R.; Supervision, M.S.G. and M.S.R.; Visualization, A.Y.B. and A.V.P.; Writing—original draft, A.Y.B.; writing—review and editing, M.S.R., M.S.G., S.K.G., M.D.L., S.Z., A.V.P., and J.G.; All authors have read and agree to the published version of the manuscript.

**Funding:** This study was supported by the Russian Science Foundation under gran<sup>t</sup> 18-14-00358.

**Acknowledgments:** The study was supported by research facilities of St. Petersburg State University "Center for Culture Collection of Microorganisms", "Molecular and Cell Technologies", and "Chromas".

**Conflicts of Interest:** The authors declare no conflict of interest.
