European journal of protistology最新文献

This study investigated the dynamics of reciprocal phenotypic plasticity entailing inducible defense and offense in freshwater ciliate communities in response to altered resource supply and the extent of intraspecific trait variation. Communities consisted of Euplotes octocarinatus (intraguild prey) capable of inducible defense to escape predation, Stylonychia mytilus (intraguild predator) capable of inducible offense to expand its prey spectrum, and Cryptomonas sp. (algal resource). The extent of inducible defense was tested in ten different Euplotes strains in response to freeze-killed Stylonychia concentrate, revealing significant differences in their width and length development. In a subsequent 30-day experiment, four strains were incubated in monoculture and mixture with Stylonychia under continuous and pulsed microalgae supply. The polyclonal Euplotes population outperformed the monoclonal populations, except one, which developed the most pronounced inducible defense and retained the highest biovolume. Stylonychia fluctuated in size, but dominated all communities irrespective of clonal composition. Pulsed resource supply promoted biovolume production of both species. However, periods of resource depletion resulted in more Stylonychia resting cysts, allowing Euplotes to resume growth. Our study provides new insights into interactions of induced defense and intraguild predation under variable environmental conditions, emphasizing the relevance of intraspecific trait variation for predator–prey interactions and community dynamics.

Small chrysomonads are important bacterivores in aquatic ecosystems with a high molecular diversity compared to low morphological differences observed by light microscopy. The high diversity of these morphologically almost indistinguishable species leads to the question to which extent their functional role in ecosystems differs and how their ecological traits can be defined. The present study investigates the prey size and population growth rate of different chrysomonad species. Eleven phylogenetically well-defined strains representing seven strains of heterotrophic and four strains of mixotrophic chrysomonads were compared. All investigated strains belonged to the same functional group of bacterivorous flagellates, feeding on the same bacteria size range, while population growth rates of chrysomonads depended on nutritional strategy and species-specific differences. We observed a high individual variability of growth rates within a population. Our results point to the necessity to consider not only differences in ecological traits among species but also among specimens within a population.

Euplotes baugilensis n. sp. was discovered in a temporary puddle that formed after rainfall on a mountain footpath near Gangneung-Wonju National University in Gangneung, South Korea. After isolation, a pure culture was established, and the new species was examined using live observation, silver-impregnation (protargol and ‘wet’ silver nitrate), scanning electron microscopy, and the analysis of the 18S rRNA gene sequence. Morphologically, E. baugilensis n. sp. is characterized by small body size (on average 49 × 31 µm in vivo), 9 ordinary fronto-ventral cirri (cirrotype-9) with one reduced cirrus V/2 (composed of four non-ciliated basal bodies), 5 transverse cirri, 7 or 8 dorsolateral kineties, 6 dorsal prominent ridges, and a dargyrome (silverline system) of double type. In this study, we have used a combination of morphological and molecular techniques to characterize E. baugilensis n. sp. and determine its phylogenetic position within the genus Euplotes. Molecular analysis using 18S rRNA gene sequences indicated that E. baugilensis n. sp. is most closely related to E. curdsi (with a sequence identity of 96.8 %).

Catalases (CATs) are ubiquitous antioxidant enzymes that prevent cellular oxidative damage through the decomposition of H₂O₂. However, there is relatively little information on CAT in the worldwide-distributed freshwater green alga Closterium ehrenbergii. Here, we cloned the full-length catalase cDNA from C. ehrenbergii (CeCAT) and characterized its structural features and expressional responses against aquatic contaminants. The open reading frame of CeCAT was determined to be 1476 bp, encoding 491 amino acids with a theoretical molecular mass of 56.1 kDa. The CeCAT protein belongs to the NADPH-binding CAT family and might be located in the cytosol. BLAST and phylogenetic results showed that CeCAT had a high identity with CAT proteins from other microalgae and the water lily Nymphaea colorata (Streptophyta). The transcriptional levels of CeCAT were significantly upregulated by the metal copper and herbicide atrazine, but little affected by other tested metals (Ni and Cr) and endocrine-disrupting chemicals (polychlorinated biphenyl, PCB). The maximum expression was registered under 0.1 mg/L CuCl₂ and 0.2 mg/L CuSO₄ exposures. In addition, excess copper considerably increased production of reactive oxygen species in the cells. These results suggest that CeCAT may function to defend against oxidative stress in green algae and can respond specifically to different kinds of metals and herbicides.

The function of recirculating aquaculture systems (RAS) relies on microbial communities, which convert toxic, fish-excreted ammonia into substances that can provide nutrients to plants as in the case of aquaponics systems. In the present study, heterotrophic protist communities of experimental sea water RAS and freshwater aquaponics systems were investigated using microscopy to characterize their diversity, natural abundance, and potential growth rates. Heterotrophic protist abundance was low (732 ± 21 to 5451 ± 118 ciliates L⁻¹ and 58 ± 8 to 147 ± 18 nanoflagellates mL⁻¹ in the aquaponics system and 78 ± 28 to 203 ± 48 ciliates L⁻¹ in the RAS), which is in line with values typically reported for rivers. In the aquaponics system, ciliates grew faster in the fish rearing tanks (1.9 ± 0.01 to 1.21 ± 0.03 d⁻¹ compared to 0.54 ± 0.03 to 0.79 ± 0.05 d⁻¹ in the other compartments), while heterotrophic nanoflagellates grew slower in drain tanks downstream of the hydroponics compartment (0.5 ± 0.3 to 1.37 ± 0.05 d⁻¹ and 4.09 ± 0.11 d⁻¹ to 6.03 ± 0.34 d⁻¹in the other compartments). Results indicated distinct niches and reduced microeukaryotic diversity at the end of the system’s operation cycle.

The ciliate Paramecium bursaria possesses cell organelles called trichocysts that have defensive functions. Paramecium bursaria is capable of symbiosis with Chlorella variabilis, and the symbiotic algae are situated in close proximity to the trichocysts. To clarify the relationship between trichocysts in P. bursaria and the presence or absence of the intracellular symbiotic C. variabilis, this study compared the regeneration capacity of trichocysts in alga-free and algae-bearing P. bursaria. In addition, trichocyst protein abundance was measured when alga-free P. bursaria specimens were artificially infected with Chlorella. After completely removing trichocysts from P. bursaria cells by treatment with lysozyme and observing them after 24 h, the percentage of regenerating trichocysts in the entire cell was significantly higher in alga-free cells than that in algae-bearing cells. We also developed a simple method for the isolation of high-purity trichocysts to quantify trichocyst protein amounts. There was a significant difference in the trichocyst protein abundance of P. bursaria before and one week after mixing with Chlorella (i.e., after the establishment of symbiosis with algae). This study shows the importance of trichocysts in alga-free P. bursaria as well as their competition with symbiotic C. variabilis for attachment sites during the algal infection process.

Protists can endure challenging environments sustaining key ecosystem processes of the microbial food webs even under aridic or hypersaline conditions. We studied the diversity of protists at different latitudes of the Atacama Desert by massive sequencing of the hypervariable region V9 of the 18S rRNA gene from soils and microbial mats collected in the Andes. The main protist groups in soils detected in active stage through cDNA were cercozoans, ciliates, and kinetoplastids, while the diversity of protists was higher including diatoms and amoebae in the microbial mat detected solely through DNA. Co-occurrence networks from soils indicated similar assemblages dominated by amplicon sequence variants (ASVs) identified as Rhogostoma, Euplotes, and Neobodo. Microbial mat networks, on the other hand, were structured by ASVs classified as raphid-pennate diatoms and amoebae from the genera Hartmannella and Vannella, mostly negatively correlated to flagellates and microalgae. Additionally, our phylogenetic inferences of ASVs classified as Euplotes, Neobodo, and Rhogostoma were supported by sequence data of strains isolated during this study. Our results represent the first snapshot of the diversity patterns of culturable and unculturable protists and putative keystone taxa detected at remote habitats from the Atacama Desert.

The morphology and molecular phylogeny of a new ciliate, Conchophthirus sinanodontae n. sp., which was discovered in the freshwater mussel Sinanodonta woodiana (Lea, 1834) from the Chilsancheon River, Buyeo-gun, South Korea, were investigated. The new species was characterized and could be distinguished from congeners by a combination of characters including the ovate body outline, four to six oral polykinetids deeply embedded in the upper wall of the buccal cavity, six to ten vestibular kineties, 34–49 ventral and 36–53 dorsal somatic kineties. The genetic differences among C. sinanodontae n. sp. and other congeners with available 18S rDNA sequences further support its distinctness. Moreover, the phylogenetic analyses based on the 18S rDNA sequences show that the new species clusters with other congeners, corroborating the monophyly of the genus Conchophthirus. The Conchophthirus clade nests within the cluster of Dexiotricha spp., Loxocephalus luridus, and Haptophrya spp.

Cyphoderia compressa has only been described from supralittoral environments, as a psammobiont, with salinities from 1.33 to 36.00 ‰. Other Cyphoderia species such as those in the C. ampulla species complex are more ecologically and environmentally widespread, occurring as free-living individuals within water bodies or in association with vegetation, and over a wider salinity range, including freshwater. We postulate that C. compressa may not be as restricted in terms of its environmental or ecological distribution. To this end, we examined a variety of water and sediment samples from Scottish localities, ranging from supralittoral to inland freshwater environments. The Scottish material occurs as a psammobiont within supralittoral beach sands and is newly recorded within sands from freshwater to brackish stream sections and along the margin of the freshwater Loch Lomond. It is also recorded from freshwater to brackish settings as part of the stream and pond water biota, associated biofilm and vegetative material. Test morphology is more variable than previously appreciated, including those with a papillate fundus, and many that are not as laterally compressed as typified by the species. Differences in plate morphology and size were also noted, as well as a novel arcuate cross-cutting ridged cement structure, that is restricted to C. compressa.

The phylogeny of brown algae (Phaeophyceae) has undergone extensive changes in the recent past due to regular new scientific insights. We used nuclear 18S rDNA with an extensive dataset, aiming to increase the accuracy and robustness of the reconstructed phylogenetic trees using a simultaneous sequence-structure approach. Individual secondary structures were generated for all 18S rDNA sequences. The sequence-structure information was encoded and used for an automated simultaneous sequence-structure alignment. Neighbor-joining and profile neighbor-joining trees were calculated based on 186 phaeophycean sequence-structure pairs. Additionally, sequence-structure neighbor-joining, maximum parsimony and maximum likelihood trees were reconstructed on a representative subset. Using a similar approach, ITS2 rDNA sequence-structure information was used to reconstruct a neighbor-joining tree including 604 sequence-structure pairs of the Laminariales. Our study results are in significant agreement with previous single marker 18S and ITS2 rDNA analyses. Moreover, the 18S results are in wide agreement with recent multi-marker analyses. The bootstrap support was significantly higher for our sequence-structure analysis in comparison to sequence-only analyses in this study and the available literature. This study supports the simultaneous inclusion of sequence-structure data at least for 18S to obtain more accurate and robust phylogenetic trees compared to sequence-only analyses.