Description of Flexiglena gen. nov. and new members of Discoplastis and Euglenaformis (Euglenida)

The genus Eutreptiella (Euglenophyceae/Euglenozoa) across its global distribution range

The genus Eutreptiella (Euglenophyceae/Euglenozoa) comprises unicellular organisms known for their photosynthetic capacity and significant role in marine ecosystems. This review highlights the taxonomic, ecological, and biotechnological characteristics of Eutreptiella species, emphasizing their morphological and genomic adaptations. Eutreptiella species exhibit high phenotypic plasticity, enabling adaptation to various environmental conditions, from nutrient-rich waters to high-salinity conditions. They play a crucial role in primary production and nutrient cycling in marine ecosystems. Genetic and transcriptomic studies have revealed their complex regulatory mechanisms and potential for biofuel and nutraceutical production. Eutreptiella blooms significantly impact local ecosystems, influencing nutrient availability and community dynamics. Additionally, interactions with associated bacteria enhance their growth and metabolic capabilities. The genus shows substantial genetic variability, suggesting potential misidentifications or a polyphyletic nature. Further comprehensive studies are needed to clarify their taxonomy and evolutionary relationships. Understanding and managing Eutreptiella populations is essential to leverage their biotechnological potential and ensure the health of marine ecosystems.

Biodiversity of autotrophic euglenids based on the group specific DNA metabarcoding approach

This study reports a comprehensive analysis of photoautotrophic euglenids' distribution and biodiversity in 16 small water bodies of various types (including fish ponds, field ponds, rural ponds and park ponds) located in three regions of Poland: Masovia, Masuria and Pomerania during a period of three years. By employing a euglenid specific barcode marker and a curated database of V2 18S rDNA sequences it was possible to identify 97.7 % of euglenid reads at species level. A total of 152 species classified in 13 genera were identified. The number of euglenid species found in one pond varied from 40 to 102. The most common species were Euglena agilis and Euglenaria caudata, found in every analysed waterbody. The highest number of observed species belonged to Trachelomonas and Phacus. Certain species exhibited a tendency to coexist, suggesting the presence of distinct species assemblages. Among them, the most distinctive cluster was associated with water bodies located in the Masuria region, characterized also by the greatest species richness, including many very rare species: Euglenaformis chlorophoenicea, Lepocinclis autumnalis, L. marssonii, Trachelomonas eurystoma, T. manschurica, T. mucosa, T. zuberi, T. zuberi var. nepos.

Discovery of a new photosynthetic euglenoid in Poland: Euglena mazurica sp. nov. (Euglenales, Euglenaceae)

Herein we describe a new photosynthetic euglenoid species found in Poland - Euglena mazurica. A large population exists in a small, eutrophic body of water located in a pasture near Mikołajki town inside the Masurian Landscape Park (covering a part of the Masurian Lake District in Poland). The unique cell shape (corkscrew-like) discerns it well from other previously described euglenoid species with metabolic cells. The new species possesses two plate-like chloroplasts each with a pyrenoid accompanied by two paramylon caps placed on either side of it (diplopyrenoids). On the phylogenetic tree, the new species is situated within the Euglena clade. Though it is a sister branch to three clades - one representing the similar Euglena agilis, characterized by its fusiform cells and two chloroplasts with diplopyrenoids, the two species are clearly morphologically and molecularly distinct.

Single-cell genomics revealed Candidatus Grellia alia sp. nov. as an endosymbiont of Eutreptiella sp. (Euglenophyceae)

Though endosymbioses between protists and prokaryotes are widespread, certain host lineages have received disproportionate attention what may indicate either a predisposition to such interactions or limited studies on certain protist groups due to lack of cultures. The euglenids represent one such group in spite of microscopic observations showing intracellular bacteria in some strains. Here, we perform a comprehensive molecular analysis of a previously identified endosymbiont in the Eutreptiella sp. CCMP3347 using a single cell approach and bulk culture sequencing. The genome reconstruction of this endosymbiont allowed the description of a new endosymbiont Candidatus Grellia alia sp. nov. from the family Midichloriaceae. Comparative genomics revealed a remarkably complete conjugative type IV secretion system present in three copies on the plasmid sequences of the studied endosymbiont, a feature missing in the closely related Grellia incantans. This study addresses the challenge of limited host cultures with endosymbionts by showing that the genomes of endosymbionts reconstructed from single host cells have the completeness and contiguity that matches or exceeds those coming from bulk cultures. This paves the way for further studies of endosymbionts in euglenids and other protist groups. The research also provides the opportunity to study the diversity of endosymbionts in natural populations.

Taxonomy of a New Parasitic Euglenid, Euglenaformis parasitica sp. nov. (Euglenales, Euglenaceae) in Ostracods and Rhabdocoels

Parasitic euglenids have rarely been studied. We found parasitic euglenids in two species of ostracods (Cyprinotus cassidula, Dolerocypris sinensis) and two species of rhabdocoels (Mesostoma lingua, Microdalyellia armigera) in a rice field. These parasites grew and proliferated inside the host body. These parasites had pellicle strips, one emergent flagellum, and a red stigma, but no chloroplasts, and showed euglenoid movement. Inside the living host, they did not have emergent flagella and moved only by euglenoid movement, but when the host died or the parasites were isolated from the host, they extended their flagella and switched to swimming movement. We conclude that the parasites found in the four hosts that we examined are of the same species, considering the morphological characteristics and identities in the nSSU and nLSU rDNA sequences of those parasites. Molecular phylogenetic analysis showed that the parasite formed a clade with the free-living photoautotrophic species of Euglenaformis, with moderate statistical support. Therefore, the parasite is a secondary osmotroph derived from a photoautotrophic ancestor. Based on the results of morphological observation and molecular phylogenetic analysis, we propose a new species of parasitic euglenid, Euglenaformis parasitica sp. nov.

Challenging the Importance of Plastid Genome Structure Conservation: New Insights From Euglenophytes

Plastids, similar to mitochondria, are organelles of endosymbiotic origin, which retained their vestigial genomes (ptDNA). Their unique architecture, commonly referred to as the quadripartite (four-part) structure, is considered to be strictly conserved; however, the bulk of our knowledge on their variability and evolutionary transformations comes from studies of the primary plastids of green algae and land plants. To broaden our perspective, we obtained seven new ptDNA sequences from freshwater species of photosynthetic euglenids-a group that obtained secondary plastids, known to have dynamically evolving genome structure, via endosymbiosis with a green alga. Our analyses have demonstrated that the evolutionary history of euglenid plastid genome structure is exceptionally convoluted, with a patchy distribution of inverted ribosomal operon (rDNA) repeats, as well as several independent acquisitions of tandemly repeated rDNA copies. Moreover, we have shown that inverted repeats in euglenid ptDNA do not share their genome-stabilizing property documented in chlorophytes. We hypothesize that the degeneration of the quadripartite structure of euglenid plastid genomes is connected to the group II intron expansion. These findings challenge the current global paradigms of plastid genome architecture evolution and underscore the often-underestimated divergence between the functionality of shared traits in primary and complex plastid organelles.

Toward the robust resolution of taxonomic ambiguity within Lepocinclis (Euglenida) based on DNA sequencing and morphology

DNA sequences were analyzed for three groups of species from the Lepocinclis genus (L. acus-like, L. oxyuris-like, and L. tripteris-like) along with cellular morphology. Phylogenetic analyses were based on nuclear SSU rDNA, LSU rDNA, and plastid-encoded LSU rDNA. DNA sequences were obtained from species available in culture collections (L. acus SAG 1224-1a and UTEX 1316) and those isolated directly from the environment in Poland (48 isolates), resulting in 79 new sequences. The obtained phylogenetic tree of Lepocinclis included 27 taxa, five of which are presented for the first time (L. convoluta, L. gracillimoides, L. longissima, L. pseudospiroides, and L. torta) and nine taxonomically verified and described. Based on morphology, literature data, and phylogenetic analyses, the following species were distinguished: in the L. acus-like group, L. longissima and L. acus; in the L. tripteris-like group, L. pseudospiroides, L. torta, and L. tripteris; in the L. oxyuris-like group, L. gracillimoides, L. oxyuris var. oxyuris, and L. oxyuris var. helicoidea. For all verified species, diagnostic descriptions were emended, nomenclatural adjustments were made, and epitypes were designated.

Euglenozoa: taxonomy, diversity and ecology, symbioses and viruses

Euglenozoa is a species-rich group of protists, which have extremely diverse lifestyles and a range of features that distinguish them from other eukaryotes. They are composed of free-living and parasitic kinetoplastids, mostly free-living diplonemids, heterotrophic and photosynthetic euglenids, as well as deep-sea symbiontids. Although they form a well-supported monophyletic group, these morphologically rather distinct groups are almost never treated together in a comparative manner, as attempted here. We present an updated taxonomy, complemented by photos of representative species, with notes on diversity, distribution and biology of euglenozoans. For kinetoplastids, we propose a significantly modified taxonomy that reflects the latest findings. Finally, we summarize what is known about viruses infecting euglenozoans, as well as their relationships with ecto- and endosymbiotic bacteria.