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Trachelomonas hispida var. coronata is one of the most widely reported varieties of T . hispida from water bodies worldwide. The specimens of this variety, apart from their species‐specific features, such as an ellipsoidal lorica covered with strong, sharp spines, have a crown consisting of long spines surrounding the apical pore opening. The process of lorica formation is poorly understood, and in the few studies dealing with this topic, results indicate that these taxa and the entire species can produce lorica completely devoid of spines, a diacritic feature of the species. In our study, we observed in detail the formation process of the lorica in this taxon under different chemical conditions in relation to the concentration of the basic elements, Fe and Mn, which are saturated in trachelomonad lorica. The results showed that in the Fe‐enriched medium, monads formed delicate, porous, spiny envelopes, whereas in the Mn‐enriched medium, the loricae were more solid and less porous and had weaker developed spines; rather, they were in the form of short papillae. Differences were also observed in the structure surrounding the apical pore, which was developed differently in the two sets of media modifications (Fe‐ or Mn‐supplemented media). We also observed different elemental compositions and colouration of loricae of cells growing in different media. This revealed that the features considered during the process of species identification are very unstable making the entire exercise highly complicated. Our research also shows that a broad discussion of the problem should be undertaken, and modern methods must be developed to unravel the complexities not only within the species but also within the entire Trachelomonas .

This research is the first taxonomic approach about the microalgae inhabiting shallow acidophilus freshwater bodies (Chapito pool, “small dam” and Tepual stream) within the Katalapi Park, X Region, Chile. A total of 80 taxa were identified based on morphocytological attributes, being the Streptophyta-Zygnematophyceae the most abundant group with a dominance of Desmidiaceae (47 species), follow by Cyanobacteria (14), Euglenophyceae (12), Chlorophyta-Chlorophyceae (5), and Dinophyceae and Ochrophyta-Raphidophyceae with one taxon each group. The genera with the higher number of species were Cosmarium (12), Closterium (11) and Staurastrum (8). The pH ranged from 5.0 to 6.1 during the recollection period. Most of the desmids species identified (70.2 %) are from acidophilus environments, 48.6 % are indicators of mesotrophy and 21.6% of meso-oligotrophic habitats. Twenty-four species are cited for the first time for Chile. Although the study was restricted to a relatively small area, the results suggest that a great diversity of microalgae might be also found in similar ecological areas within the country.

The classification of Trachelomonas and Strombomonas is based on the morphology of loricae, which may not reflect phylogenetic relationships. There are different views on the relationship between the two genera. It is thus important for researchers to classify the two genera based on more characteristics besides loricae, such as protoplast and molecular data, and to establish a natural classification system. In this study, 29 strains (13 species) of Trachelomonas and 12 strains (eight species) of Strombomonas were collected from various locations in China. The morphological characteristics of Trachelomonas and Strombomonas were observed in the field and culture conditions, and the sequences of nuclear SSU rDNA, nuclear LSU rDNA, plastid-encoded LSU rDNA and plastid-encoded LSU rDNA of strains were obtained. We constructed a phylogenetic tree by combining four gene sequences with maximum likelihood and Bayesian methods. Based on the development of the loricae, it was found that the shape of the loricae and the presence or absence of the collar were relatively stable in culture, while the length of the collar presence or absence of spines and the color of the loricae changed. The phylogenetic tree showed that Trachelomonas and Strombomonas were sister branches, which supported Trachelomonas and Strombomonas as independent genera. Taxa in the genus Strombomonas sorted into two clades and Trachelomonas sorted into five strongly supported clades. Key morphological features could be attributed to each of the clades.

Euglenids exhibit an unconventional motility strategy amongst unicellular eukaryotes, consisting of large-amplitude highly concerted deformations of the entire body (euglenoid movement or metaboly). A plastic cell envelope called pellicle mediates these deformations. Unlike ciliary or flagellar motility, the biophysics of this mode is not well understood, including its efficiency and molecular machinery. We quantitatively examine video recordings of four euglenids executing such motions with statistical learning methods. This analysis reveals strokes of high uniformity in shape and pace. We then interpret the observations in the light of a theory for the pellicle kinematics, providing a precise understanding of the link between local actuation by pellicle shear and shape control. We systematically understand common observations, such as the helical conformations of the pellicle, and identify previously unnoticed features of metaboly. While two of our euglenids execute their stroke at constant body volume, the other two exhibit deviations of about 20% from their average volume, challenging current models of low Reynolds number locomotion. We find that the active pellicle shear deformations causing shape changes can reach 340%, and estimate the velocity of the molecular motors. Moreover, we find that metaboly accomplishes locomotion at hydrodynamic efficiencies comparable to those of ciliates and flagellates. Our results suggest new quantitative experiments, provide insight into the evolutionary history of euglenids, and suggest that the pellicle may serve as a model for engineered active surfaces with applications in microfluidics.

Temporary ponds in agricultural landscapes, highly vulnerable to anthropogenic pressure and climatic variation, constitute unique habitats for microalgae and endangered filter feeders (large branchiopods). Such ponds play a crucial role in the functioning of farmland ecosystem, yet they remain largely understudied. Our study is the first to examine changes in phytoplankton communities in temporary kettle hole ponds in relation to rapid shifts in biotic (large branchiopods) and physical and chemical parameters of water. We conducted our research over a three-year cycle (in nine ponds in western Poland), with sampling starting in spring when inundation usually occurs, and continuing until the ponds dried out. Among 406 phytoplankton taxa (mainly euglenoids, but also diatoms and chlorophytes), locally rare species (e.g. Desmatractum indutum ) were noted. When branchiopods occurred in the ponds, the phytoplankton communities shifted towards unicellular chlorophytes. Furthermore, nitrogen forms, temperature, conductivity, and pH were the abiotic factors altering the studied communities. Surprisingly, the diversity of phytoplankton species did not decrease with increasing temperature, which is inconsistent with the trend observed in permanent water bodies. The study identified specific drivers of phytoplankton community structure and dynamics, underscoring their ecological significance and management implications. These insights will be valuable for future conservation strategies of temporary ponds, crucial in sustaining biodiversity in farmland areas.

Background The phylum Euglenozoa is a group of flagellated protists comprising the diplonemids, euglenids, symbiontids, and kinetoplastids. The diplonemids are highly abundant and speciose, and recent tools have rendered the best studied representative, Diplonema papillatum , genetically tractable. However, despite the high diversity of diplonemids, their lifestyles, ecological functions, and even primary energy source are mostly unknown. Results We designed a metabolic map of D. papillatum cellular bioenergetic pathways based on the alterations of transcriptomic, proteomic, and metabolomic profiles obtained from cells grown under different conditions. Comparative analysis in the nutrient-rich and nutrient-poor media, as well as the absence and presence of oxygen, revealed its capacity for extensive metabolic reprogramming that occurs predominantly on the proteomic rather than the transcriptomic level. D. papillatum is equipped with fundamental metabolic routes such as glycolysis, gluconeogenesis, TCA cycle, pentose phosphate pathway, respiratory complexes, β-oxidation, and synthesis of fatty acids. Gluconeogenesis is uniquely dominant over glycolysis under all surveyed conditions, while the TCA cycle represents an eclectic combination of standard and unusual enzymes. Conclusions The identification of conventional anaerobic enzymes reflects the ability of this protist to survive in low-oxygen environments. Furthermore, its metabolism quickly reacts to restricted carbon availability, suggesting a high metabolic flexibility of diplonemids, which is further reflected in cell morphology and motility, correlating well with their extreme ecological valence.

Background and aims- Phytoplankton samples were taken from a periodic, small and very shallow former clay-pit pond in eastern Poland near Lublin city. Diversity of the euglenophyte community was assessed during the period 2002-2004 and in 2014. Methods- Water samples were collected with a 20 μm plankton net and with a slime aspirator (20 ml capacity) from the surface of the bottom. One aliquot of each sample was fixed for SEM observation; the fresh part of the sample was analysed using light microscope. Physical and chemical properties of the water (pH, temperature, conductivity, phosphates and ammonium salt contents) were measured. Diversity indices were calculated (Shannon-Wiener, evenness, Margalef and Simpson) and UPGMA cluster analysis was applied to discern differences among euglenoid assemblages. Key results- In total, 63 euglenophyte taxa were found. The euglenophyte community was dominated by species belonging to the Trachelomonas genus (29 taxa). The most abundant and constant component were widespread and common species such as T. caudata, T . hispida, T . intermedia, T. volvocina and T. volvocinopsis. They usually occurred in very high densities. We also found some rarely reported euglenophytes including Euglena granulata, Trachelomonas lemmermannii, and T. sydneyensis .Conclusions- Euglenophytes were, with a few exceptions, the only group inhabiting the pond. Representatives of other groups such as diatoms or Scenedesmus species were recorded only occasionally. Nearly half of the taxa that were recorded in the first period (2002-2004) were found again after ten years. Of special concern was taxa belonging to the genus Trachelomonas. Trachelomonads, although known to represent taxa preferring waters moderately rich in nutrients, were very numerous in the investigated pond, which was enriched in phosphorus and nitrogen compounds.

Background Members of Euglenozoa (Discoba) are known for unorthodox rDNA organization. In Euglenida rDNA is located on extrachromosomal circular DNA. In Kinetoplastea and Euglenida the core of the large ribosomal subunit, typically formed by the 28S rRNA, consists of several smaller rRNAs. They are the result of the presence of additional internal transcribed spacers (ITSs) in the rDNA. Diplonemea is the third of the main groups of Euglenozoa and its members are known to be among the most abundant and diverse protists in the oceans. Despite that, the rRNA of only one diplonemid species, Diplonema papillatum , has been examined so far and found to exhibit continuous 28S rRNA. Currently, the rDNA organization has not been researched for any diplonemid. Herein we investigate the structure of rRNA genes in classical (Diplonemidae) and deep-sea diplonemids (Eupelagonemidae), representing the majority of known diplonemid diversity. The results fill the gap in knowledge about diplonemid rDNA and allow better understanding of the evolution of the fragmented structure of the rDNA in Euglenozoa. Results We used available genomic (culture and single-cell) sequencing data to assemble complete or almost complete rRNA operons for three classical and six deep-sea diplonemids. The rDNA sequences acquired for several euglenids and kinetoplastids were used to provide the background for the analysis. In all nine diplonemids, 28S rRNA seems to be contiguous, with no additional ITSs detected. Similarly, no additional ITSs were detected in basal prokinetoplastids. However, we identified five additional ITSs in the 28S rRNA of all analysed metakinetoplastids, and up to twelve in euglenids. Only three of these share positions, and they cannot be traced back to their common ancestor. Conclusions Presented results indicate that independent origin of additional ITSs in euglenids and kinetoplastids seems to be the most likely. The reason for such unmatched fragmentation remains unknown, but for some reason euglenozoan ribosomes appear to be prone to 28S rRNA fragmentation.

The classification of Trachelomonas and Strombomonas is based on the morphology of loricae, which may not reflect phylogenetic relationships. There are different views on the relationship between the two genera. It is thus important for researchers to classify the two genera based on more characteristics besides loricae, such as protoplast and molecular data, and to establish a natural classification system. In this study, 29 strains (13 species) of Trachelomonas and 12 strains (eight species) of Strombomonas were collected from various locations in China. The morphological characteristics of Trachelomonas and Strombomonas were observed in the field and culture conditions, and the sequences of nuclear SSU rDNA, nuclear LSU rDNA, plastid-encoded LSU rDNA and plastid-encoded LSU rDNA of strains were obtained. We constructed a phylogenetic tree by combining four gene sequences with maximum likelihood and Bayesian methods. Based on the development of the loricae, it was found that the shape of the loricae and the presence or absence of the collar were relatively stable in culture, while the length of the collar presence or absence of spines and the color of the loricae changed. The phylogenetic tree showed that Trachelomonas and Strombomonas were sister branches, which supported Trachelomonas and Strombomonas as independent genera. Taxa in the genus Strombomonas sorted into two clades and Trachelomonas sorted into five strongly supported clades. Key morphological features could be attributed to each of the clades.

Background Nuclear genes of euglenids contain two major types of introns: conventional spliceosomal and nonconventional introns. The latter are characterized by variable non-canonical borders, RNA secondary structure that brings intron ends together, and an unknown mechanism of removal. Some researchers also distinguish intermediate introns, which combine features of both types. They form a stable RNA secondary structure and are classified into two subtypes depending on whether they contain one (intermediate/nonconventional subtype) or both (conventional/intermediate subtype) canonical spliceosomal borders. However, it has been also postulated that most introns classified as intermediate could simply be special cases of conventional or nonconventional introns. Results Sequences of tubB , hsp90 and gapC genes from six strains of Euglena agilis were obtained. They contain four, six, and two or three introns, respectively (the third intron in the gapC gene is unique for just one strain). Conventional introns were present at three positions: two in the tubB gene (at one position conventional/intermediate introns were also found) and one in the gapC gene. Nonconventional introns are present at ten positions: two in the tubB gene (at one position intermediate/nonconventional introns were also found), six in hsp90 (at four positions intermediate/nonconventional introns were also found), and two in the gapC gene. Conclusions Sequence and RNA secondary structure analyses of nonconventional introns confirmed that their most strongly conserved elements are base pairing nucleotides at positions +4, +5 and +6/ -8, −7 and −6 (in most introns CAG/CTG nucleotides were observed). It was also confirmed that the presence of the 5' GT/C end in intermediate/nonconventional introns is not the result of kinship with conventional introns, but is due to evolutionary pressure to preserve the purine at the 5' end. However, an example of a nonconventional intron with GC-AG ends was shown, suggesting the possibility of intron type conversion between nonconventional and conventional. Furthermore, an analysis of conventional introns revealed that the ability to form a stable RNA secondary structure by some introns is probably not a result of their relationship with nonconventional introns. It was also shown that acquisition of new nonconventional introns is an ongoing process and can be observed at the level of a single species. In the recently acquired intron in the gapC gene an extended direct repeats at the intron-exon junctions are present, suggesting that double-strand break repair process could be the source of new nonconventional introns.