The Green Tetrahymena utriculariae n. sp. (Ciliophora, Oligohymenophorea) with Its Endosymbiotic Algae (Micractinium sp.), Living in Traps of a Carnivorous Aquatic Plant

Abstract

The genus Tetrahymena (Ciliophora, Oligohymenophorea) probably represents the best studied ciliate genus. At present, more than forty species have been described. All are colorless, i.e. they do not harbor symbiotic algae, and as aerobes they need at least microaerobic habitats. Here, we present the morphological and molecular description of the first green representative, Tetrahymena utriculariae n. sp., living in symbiosis with endosymbiotic algae identified as Micractinium sp. (Chlorophyta). The full life cycle of the ciliate species is documented, including trophonts and theronts, conjugating cells, resting cysts and dividers. This species has been discovered in an exotic habitat, namely in traps of the carnivorous aquatic plant Utricularia reflexa (originating from Okavango Delta, Botswana). Green ciliates live as commensals of the plant in this anoxic habitat. Ciliates are bacterivorous, however, symbiosis with algae is needed to satisfy cell metabolism but also to gain oxygen from symbionts. When ciliates are cultivated outside their natural habitat under aerobic conditions and fed with saturating bacterial food, they gradually become aposymbiotic. Based on phylogenetic analyses of 18S rRNA and mitochondrial cox1 genes T. utriculariae forms a sister group to Tetrahymena thermophila.

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

“…Systematic revision of zoochlorellae [79], redescription of P . chlorelligerum [12], new data on green symbionts of Loxodes rostrum [71] and on Tetrahymena utriculariae [81], changed this view on algae inhabiting cytoplasm of ciliates. Comparative analysis of different Chlorella -like symbionts [79] revealed five phylogenetically distinct symbionts, namely Chlorella , Choricystis , Coccomyxa , Scenedesmus and Micractinium , which could be found in several ciliates.…”

Ecological Traits of the Algae‐BearingTetrahymena utriculariae(Ciliophora) from Traps of the Aquatic Carnivorous PlantUtricularia reflexa

“…It was predominantly composed of only a few morphologically easily distinguishable species: the newly described algae‐bearing ciliate T. utriculariae (Pitsch et al. ), the green flagellate E. agilis , and the alga S. alternans . These three taxa clearly dominated in numbers and biomass of eukaryotes (Fig.…”

“…For the quantification of the eukaryotic community, we focused on the three most prominent in terms of numbers and biomass and easily distinguishable species of protists: the ciliate T. utriculariae (Pitsch et al. ), the euglenoid flagellate, Euglena agilis (Adamec and Komárek ; Ciugulea and Triemer ), and the algal species Scenedesmus alternans . At least 300 protistan cells were counted per sample at 400X magnification via epifluorescence microscopy as described previously (Šimek et al.…”

“…Cultures of symbiont bearing ciliates were maintained for several months (Pitsch et al. ). Nevertheless, several ciliate isolates kept under aerobic conditions with saturating bacterial food gradually lost their algal symbionts (over several weeks)—even when cultures were grown at a 12 h light/12 h dark cycle.…”

“…This species is described as Tetrahymena utriculariae n. sp in our accompanying publication (Pitsch et al. ).…”