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.