Protistology

DNA of the majority of present-day eukaryotes is folded with the aid of highly conserved histone proteins to form nucleosome fibers, which further condense via interactions with histones and non-histone chromatin proteins. Dinoflagellate chromatin is unique among eukaryotes, as their chromosomes lack the histones and remain condensed throughout the cell cycle. Here, we report the results of electron microscopy study of chromatin elements inside the chromosomes of potentially toxic planktonic dinoflagellate Prorocentrum minimum. We found that chromatin fibers inside the condensed chromosomes of P. minimum form not only arch-like structures, that were repeatedly described for various dinoflagellate species, but also rosette-like complexes with chromatin fibers radiating from its electron-dense center. The effects of histone loss in the evolution of dinoflagellates are discussed within the frames of the hierarchical chromatin folding paradigm.

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Ciliates are a morphologically diverse group of protists inhabiting aquatic and terrestrial ecosystems. We studied the taxonomy and ecology of free-living ciliates from a freshwater marsh in Central Mexico during the period from 2012 to 2013 during both dry and rainy seasons. We found 30 ciliate species recorded for the first time from Atarasquillo marsh in Mexico, most of which are common species in freshwater ecosystems. The species richness was higher during the dry season than rainy season. Five trophic groups were observed: bacterivorous, bacteria-algae-heterotrophic flagellate consumers (BAF-consumers), omnivorous, predators, and mixotrophic species. The trophic group composition changed according to the season and the environmental conditions, e.g. vegetation and water level. Generally bacterivorous ciliates were more frequent during the rainy season, meanwhile the omnivorous during the dry season; thus, the feeding strategies in ciliates were different between both seasons. Due to the fact that Atarasquillo marsh is in a deterioration process, ciliate records could be used to assess water quality.

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The taxonomic composition and dynamics of numerical density of alien tintinnid species in the bays and harbours of the northeastern Black Sea were studied. The highest number of non-indigenous tintinnid species (9 species) were found in the Novorossiysk Harbour, the lowest number of species (4 species) in the Gelendzhik Bay, and two species - in the harbours of Sochi and Sukhum. In the Novorossiysk Harbour, Amphorellopsis acuta Schmidt, 1902 (average density 2.1 ± 1×10 cells/ m), Dartintinnus alderae Smith, Song, Gavrilova, Kurilov, Liu, McManus and Santoferrara, 2018 (average density 1.34 ± 0.6×10 cells/m), and Tintinnopsis tocantinensis Kofoid and Campbell, 1929 (average density 0.73 ± 0.31×10 cells/ m) were dominant during the late summer-autumn season of 2012-2017. The summarized abundance of tintinnid ciliates was almost six to eight times higher than in the late 1990s. This study report Rhizodomus tagatzi Strelkov and Wirketis, 1950 and Tintinnopsis mortensenii Schmidt, 1902 for the first time from the northeastern Black Sea. The origin of alien species populations in the northeastern Black Sea have been linked probably to their introduction by shipping.

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Amoebae of the genus Thecamoeba (Amoebozoa, Discosea, Thecamoebida) are among the most widely distributed and best-known species of naked lobose amoebae. However, the number of available ultrastructural studies of these organisms remains low. The most of them are dated back to 1960-1970 and virtually no modern data appeared in the literature, except for the newly described Thecamoeba aesculea. As a result, we have no complete reports on the fine structure of many widely distributed and most trivial Thecamoeba species. The present study provides the complete ultrastructure of Thecamoeba quadrilineata strain CCAP 1583/10. The studied strain is also known to serve as a host for Nucleophaga amoebae - an intranuclear parasite belonging to the Opisthosporidia clade, so the investigation of non-infected amoebae provides “reference” data for studying the infection process and intracellular development of this parasite.

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Species composition and morphology of heterotrophic flagellates in littoral and supralittoral zones of the Black Sea (southwestern part of the Crimea) were studied in September 2017. A total of 77 species and forms of heterotrophic flagellates were encountered in this survey, 35 of them are new records for the Black Sea, and one, Oscillata sevastopoliensis gen. et sp. n., was described for the first time. The most frequent were Metromonas simplex and Neobodo designis (observed in 14 samples), Lentomonas corrugata (13 samples), Amastigomonas mutabilis and Petalomonas poosilla (10 samples). Species diversity in the present study was higher in comparison with the data obtained in May 2017 in the same region. Micrographs and morphological descriptions of 20 species (Ministeria vibrans, Salpingoeca oblonga, Savillea parva, Stephanoeca apheles, S. cupula, Volkanus costatus, Cafeteria ligulifera, Paraphysomonas lucasi, Pteridomonas danica, Colponema marisrubri, Ovaloplaca salina, Clautriavia cavus, Dinema platysomum, Lentomonas corrugata, Notosolenus stutulum, N. tamanduensis, Hemistasia amylophagus, H. phaeocysticola, Heterochromonas opaca, and Oscillata sevastopoliensis gen. et sp. n.) are given.

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