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Open Access Research article

Morphology, ultrastructure, and molecular phylogeny of the ciliate Sonderia vorax with insights into the systematics of order Plagiopylida

Letizia Modeo1*, Sergei I Fokin12, Vittorio Boscaro1, Ilaria Andreoli1, Filippo Ferrantini1, Giovanna Rosati1, Franco Verni1 and Giulio Petroni1

Author affiliations

1 Unit of Protistology-Zoology, Department of Biology, University of Pisa, via A. Volta 4/6, Pisa 56126, Italy

2 Department of Invertebrate Zoology, St. Petersburg State University, Universitetskaya emb. 7/9, St. Petersburg, 199034, Russia

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Citation and License

BMC Microbiology 2013, 13:40  doi:10.1186/1471-2180-13-40

Published: 18 February 2013

Abstract

Background

Ciliates of the family Sonderiidae are common members of the eukaryotic communities in various anoxic environments. They host both ecto- and endosymbiotic prokaryotes (the latter associated with hydrogenosomes) and possess peculiar morpho-ultrastructural features, whose functions and homologies are not known. Their phylogenetic relationships with other ciliates are not completely resolved and the available literature, especially concerning electron microscopy and molecular studies, is quite scarce.

Results

Sonderia vorax Kahl, 1928 is redescribed from an oxygen-deficient, brackish-water pond along the Ligurian Sea coastlines of Italy. Data on morphology, morphometry, and ultrastructure are reported. S. vorax is ovoid-ellipsoid in shape, dorsoventrally flattened, 130 x 69 μm (mean in vivo); it shows an almost spherical macronucleus, and one relatively large micronucleus. The ventral kinetom has a “secant system” including fronto-ventral and fronto-lateral kineties. A distinctive layer of bacteria laying between kineties covers the ciliate surface. Two types of extrusomes and hydrogenosomes-endosymbiotic bacteria assemblages are present in the cytoplasm. The phylogeny based on 18S rRNA gene sequences places S. vorax among Plagiopylida; Sonderiidae clusters with Plagiopylidae, although lower-level relationships remain uncertain. The studied population is fixed as neotype and the ciliate is established as type species of the genus, currently lacking.

Conclusions

This is the first description of a representative of Sonderiidae performed with both morphological and molecular data. To sum up, many previous hypotheses on this interesting, poorly known taxon are confirmed but confusion and contradictory data are as well highlighted.

Keywords:
Ectosymbionts; FISH; Hydrogenosomes-endosymbionts assemblages; Oxygen deficient environment; Plagiopylida; Phylogeny; Silver-nitrate staining; SSU rRNA; Sulphide fauna; Ultrastructure