The existence of symbiotic relationships between prokaryotes and ciliate protozoa is known from over a century. Most studies concerned obligatory mutualistic symbiosis, whereas there is little knowledge about facultative non-mutualistic symbiotic relationships, mainly because these associations can be spatially and temporally variable in natural populations and are especially difficult to maintain in lab conditions. Nevertheless, they seem to be more widespread among ciliates than so far supposed. A research project was recently started in order to get data about such kind of association in ciliate populations living in a coastal brackish environment. During this study, we observed some individuals from a population of Frontonia sp. (Oligohymenophorea, Peniculia) showing roundish macronuclei instead of ellipsoidal ones. Observation at DIC microscope revealed the presence of some relatively large spindle-shaped objects in all macronuclei. According to the general shape and morphological features, the identification of these objects as Holospora infectious forms was hypothesized. The genus Holospora (Alphaproteobacteria, Rickettsiales) comprises bacterial endosymbionts, which are resident in the nuclear apparatus of ciliates belonging to the genus Paramecium (Oligohymenophorea, Peniculia). Their life cycle presents two different forms: a large infectious form and a smaller reproductive form. Experiments of in situ hybridization using a genus-specific probe confirmed the identification of the observed endonuclear objects as Holospora infectious forms; it made also possible to observe even the smaller reproductive forms in macronuclei that were not clearly visible at DIC observation. To further characterize this symbiont, bacterial DNA was extracted from a population of infected Frontonia sp. cells. The 16S rRNA gene sequence was obtained by touchdown PCR reaction with a-proteobacteria- specific primers and direct sequencing of reaction product. The new sequence shows a similarity value of about 95% with that of H. obtusa. Indeed, analysis of phylogenetic relationships revealed that the two sequences are firmly associated. Molecular data obtained up to now suggest the belonging of this organism to a novel species of Holospora.

Characterization of a novel Holospora-like symbiont from Frontonia (Ciliophora, Oligohymenophorea)

FOKIN, SERGEY;VANNINI, CLAUDIA;VERNI, FRANCO;PETRONI, GIULIO
2006-01-01

Abstract

The existence of symbiotic relationships between prokaryotes and ciliate protozoa is known from over a century. Most studies concerned obligatory mutualistic symbiosis, whereas there is little knowledge about facultative non-mutualistic symbiotic relationships, mainly because these associations can be spatially and temporally variable in natural populations and are especially difficult to maintain in lab conditions. Nevertheless, they seem to be more widespread among ciliates than so far supposed. A research project was recently started in order to get data about such kind of association in ciliate populations living in a coastal brackish environment. During this study, we observed some individuals from a population of Frontonia sp. (Oligohymenophorea, Peniculia) showing roundish macronuclei instead of ellipsoidal ones. Observation at DIC microscope revealed the presence of some relatively large spindle-shaped objects in all macronuclei. According to the general shape and morphological features, the identification of these objects as Holospora infectious forms was hypothesized. The genus Holospora (Alphaproteobacteria, Rickettsiales) comprises bacterial endosymbionts, which are resident in the nuclear apparatus of ciliates belonging to the genus Paramecium (Oligohymenophorea, Peniculia). Their life cycle presents two different forms: a large infectious form and a smaller reproductive form. Experiments of in situ hybridization using a genus-specific probe confirmed the identification of the observed endonuclear objects as Holospora infectious forms; it made also possible to observe even the smaller reproductive forms in macronuclei that were not clearly visible at DIC observation. To further characterize this symbiont, bacterial DNA was extracted from a population of infected Frontonia sp. cells. The 16S rRNA gene sequence was obtained by touchdown PCR reaction with a-proteobacteria- specific primers and direct sequencing of reaction product. The new sequence shows a similarity value of about 95% with that of H. obtusa. Indeed, analysis of phylogenetic relationships revealed that the two sequences are firmly associated. Molecular data obtained up to now suggest the belonging of this organism to a novel species of Holospora.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/106003
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