Rare Freshwater Ciliate Paramecium chlorelligerum Kahl, 1935 and Its Macronuclear Symbiotic Bacterium “Candidatus Holospora parva”

Abstract

Ciliated protists often form symbioses with many diverse microorganisms. In particular, symbiotic associations between ciliates and green algae, as well as between ciliates and intracellular bacteria, are rather wide-spread in nature. In this study, we describe the complex symbiotic system between a very rare ciliate, Paramecium chlorelligerum, unicellular algae inhabiting its cytoplasm, and novel bacteria colonizing the host macronucleus. Paramecium chlorelligerum, previously found only twice in Germany, was retrieved from a novel location in vicinity of St. Petersburg in Russia. Species identification was based on both classical morphological methods and analysis of the small subunit rDNA. Numerous algae occupying the cytoplasm of this ciliate were identified with ultrastructural and molecular methods as representatives of the Meyerella genus, which before was not considered among symbiotic algae. In the same locality at least fifteen other species of “green” ciliates were found, thus it is indeed a biodiversity hot-spot for such protists. A novel species of bacterial symbionts living in the macronucleus of Paramecium chlorelligerum cells was morphologically and ultrastructurally investigated in detail with the description of its life cycle and infection capabilities. The new endosymbiont was molecularly characterized following the full-cycle rRNA approach. Furthermore, phylogenetic analysis confirmed that the novel bacterium is a member of Holospora genus branching basally but sharing all characteristics of the genus except inducing connecting piece formation during the infected host nucleus division. We propose the name “Candidatus Holospora parva” for this newly described species. The described complex system raises new questions on how these microorganisms evolve and interact in symbiosis.

Are there any true marine Chlorella species? Molecular phylogenetic assessment and ecology of marine Chlorella-like organisms, including a description of Droopiella gen. nov.

“…The only genus in the Chlorellaclade containing chloroplast without a pyrenoid is the genus Meyerella (Fawley et al, 2005). This organism was found in freshwater lakes in Minnesota (USA) and as an endosymbiont in Paramecium species (Kreutz et al, 2012;Lanzoni et al, 2016).…”

Detection of a new bacterium of the family Holosporaceae (Alphaproteobacteria: Holosporales) associated with the oribatid mite Achipteria coleoptrata

“…Furthermore, we included the 16S rDNA sequences of endosymbiont of X. muta and bacteria noted in other marine hosts: Porites compressa Dana, 1846 and Hippocampus guttulatus Cuvier, 1829. In order to make the data comprehensive, we applied in the analysis also the sequences of other bacteria published in similar works (Hess et al 2016;Lanzoni et al 2016;Szokoli et al 2016a, b;Castelli et al 2018b;Potekhin et al 2018;Schrallhammer et al 2018;Tashyreva et al 2018;Fokin et al 2019) using Rickettsiales sequences as an outgroup. The bacterial sequences used in the analysis were presented in the Fig.…”

“…We conducted phylogenetic analysis based on 16S rDNA sequences of the bacterium from A. coleoptrata and endosymbionts of other host that showed sequence identity by BLASTn. Additional sequence data were included in the analysis according to literature data (Boscaro et al 2013;Schulz et al 2014;Hess et al 2016;Lanzoni et al 2016;Szokoli et al 2016a, b;Castelli et al 2018b;Potekhin et al 2018;Schrallhammer et al 2018;Tashyreva et al 2018).…”

The extracellular association of the bacterium “CandidatusDeianiraea vastatrix” with the ciliateParameciumsuggests an alternative scenario for the evolution ofRickettsiales

“…DNA was extracted with the Nucleospin Plant II kit (Macherey-Nagel), following the protocol for mycelium. All PCR reactions were performed with the TaKaRa ExTaq (TaKaRa Bio Inc), as previously described (Lanzoni et al 2016). For the molecular characterization of Paramecium 18S rRNA gene, ITS and COI gene were amplified and directly sequenced (Lanzoni et al 2016) (Supplementary material 22).…”