Systematic review of the genus Ostracodinium (Ciliophora, Entodiniomorphida, Ophryoscolecidae) and notes on the taxonomy of Ostracodinium rugoloricatum Kofoid & MacLennan, 1932

The family Ophryoscolecidae (Ciliophora, Entodiniomorphida) constitutes a diverse and monophyletic group of symbiotic ciliates of herbivorous mammals. The family includes approximately 200 species, distributed in three subfamilies and sixteen genera. The subfamily Diplodiniinae is the most diverse group in Ophryoscolecidae and comprises the genus Ostracodinium, which includes species with two retractable ciliary zones in the anterior body portion, a broad skeletal plate covering almost all the right surface of the body and a variable number of contractile vacuoles. The genus currently comprises 28 species, classified according to body size and shape, position and shape of the nuclear apparatus, number and position of contractile vacuoles, and number and shape of caudal projections. The present study performs a systematic review of the genus Ostracodinium, based on morphological and molecular data, and provides data about geographic distribution and hosts of each species.

Morphology and description of infraciliary bands pattern in four Metadinium Awerinzew & Mutafowa, 1914 species (Ciliophora, Entodiniomorphida, Ophryoscolecidae) with taxonomic notes on the genus

The genus Metadinium includes ophryoscolecid ciliates, with two retractile ciliary zones in the anterior body portion, two broad skeletal plates, a lobed macronucleus and two contractile vacuoles. Species belonging to this genus were recorded in several geographical locations and in different host species. However, they were mostly described based on a single ciliatological technique, and until now, there is only one description of the infraciliary pattern in Metadinium ciliates (Metadinium medium). The present study performs the morphological and infraciliature characterization of four species belonging to Metadinium: M. esalqum, M. minorum, M. rotundatum and M. ypsilon; and presents taxonomic notes on the genus. The oral infraciliature in these four Metadinium species corresponds to the Diplodinium-type, pattern shared with genera Diplodinium, Diploplastron, Eudiplodinium, Eremoplastron and Polyplastron. A brief review conducted highlights the difficulty of delimiting Metadinium species due to the morphological similarity among them.

The Contractile Vacuole as a Key Regulator of Cellular Water Flow in Chlamydomonas reinhardtii

ABSTRACT Most freshwater flagellates use contractile vacuoles (CVs) to expel excess water. We have used Chlamydomonas reinhardtii as a green model system to investigate CV function during adaptation to osmotic changes in culture medium. We show that the contractile vacuole in Chlamydomonas is regulated in two different ways. The size of the contractile vacuoles increases during cell growth, with the contraction interval strongly depending on the osmotic strength of the medium. In contrast, there are only small fluctuations in cytosolic osmolarity and plasma membrane permeability. Modeling of the CV membrane permeability indicates that only a small osmotic gradient is necessary for water flux into the CV, which most likely is facilitated by the aquaporin major intrinsic protein 1 (MIP1). We show that MIP1 is localized to the contractile vacuole, and that the expression rate and protein level of MIP1 exhibit only minor fluctuations under different osmotic conditions. In contrast, SEC6, a protein of the exocyst complex that is required for the water expulsion step, and a dynamin-like protein are upregulated under strong hypotonic conditions. The overexpression of a CreMIP1-GFP construct did not change the physiology of the CV. The functional implications of these results are discussed.

Morphology, morphogenesis, and molecular phylogeny of a new brackish water ciliate, Pseudourostyla cristatoides n. sp., from Songjiho lagoon on the coast of East Sea, South Korea

A new brackish water urostylid ciliate, Pseudourostyla cristatoides n. sp. was collected from Songjiho lagoon on the coast ofEast Sea, South Korea, and investigated based on morphology, morphogenesis, and 18S rRNA gene sequences.Pseudourostyla cristatoides is characterized by the following features: slender to elliptical body shape; colourless to dark greyin colour; size in vivo about 220–265 × 85–125μm; flexible and slightly contractile body with narrowly spaced extrusomes(trichocyst type) throughout the whole cell; 2 contractile vacuoles on left side of cell at about 25% and 75% of body length;84–115 adoral membranelles, 20–30 frontal cirri, 1 buccal cirrus, 2 frontoterminal cirri, 17–25 midventral pairs, 2pretransverse, 6–12 transverse cirri, 5–7 left and 4–5 right marginal rows, and 10–13 dorsal kineties; 30–106 macronuclearnodules and 3–5 micronuclei; brackish habitat (salinity 3–5‰). This new species is very similar to P. cristata, but distinguishedprimarily by contractile vacuoles (2 vs. 1 in number; positioned 25%, 75% of body length vs. ahead of mid-body), dorsalkineties (10–13 vs. 8), hyaline layer underneath pellicle (inconspicuous vs. conspicuous), habitat (brackish vs. freshwater), andparticipation of posterior cirri of rear corona in fronto-ventral-transverse cirral anlagen (yes vs. no). Additionally, intra-/inter-specific pairwise genetic distances of the 18S rRNA gene sequences supported that the Songjiho population is a novel species(intra-specific distances of 0.07–0.12% among three P. cristata populations vs. inter-specific distances of 0.93–1.00% between P. cristatoides and three P. cristata populations).