Journal of Eukaryotic Microbiology最新文献

Cryptomonad protists are ubiquitously distributed over marine and freshwater habitats. As an exception to the colored cryptomonads, the heterotrophic cryptomonads of the genus Goniomonas have an ancestral phylogenetic position. They lack any kind of chloroplast and most likely represent a basal group to those cryptomonad groups having obtained their chloroplast by secondary endosymbiosis. Earlier studies have shown a deep divergence between freshwater and marine clades of goniomonads that comprise large genetic distances between members within the group and also between the two groups of marine and freshwater taxa. Still, marine and freshwater species carry the same genus name, and to date, only a few species have been described. We therefore restructured goniomonad systematics based not only on a separation of marine and freshwater taxa, but also, taking the large genetic distances into account, on several new genera that are described. Based on morphological as well as phylogenetic data (18S rDNA sequences), this leads to the formation of the freshwater genera Limnogoniomonas n. g., Goniomonas, and Aquagoniomonas n. g. and the marine genera Neptunogoniomonas n. g., Baltigoniomonas n. g., Marigoniomonas n. g., Thalassogoniomonas n. g., Poseidogoniomonas n. g., and Cosmogoniomonas n. g. To give the restructuring process a stable basis, we additionally propose a neotype for Goniomonas truncata.

Benthic Foraminifera exhibit diverse adaptations to low oxygen (O₂) environments, including denitrification, a rare trait among eukaryotes. Denitrifying species store intracellular nitrate (NO₃⁻), possibly within vacuoles, and contribute significantly to the global marine nitrogen (N) cycle. Additionally, widespread phosphate (PO₄³⁻) accumulation suggests a role in supporting metabolism under O₂-depleted conditions. However, the organelles storing NO₃⁻ and PO₄³⁻ remain unknown, limiting the mechanistic understanding of these alternative metabolic pathways. To investigate the intracellular NO₃⁻ and PO₄³⁻ localization in the benthic foraminifera Bolivina spissa, experimental incubations under varying O₂ and NO₃⁻ conditions followed by cryogenic fixation and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) analyses were carried out. Most vacuoles were enriched in N relative to the surrounding cytoplasm, likely representing the intracellular NO₃⁻ reservoir. The elemental mapping also confirmed phosphorus (P) enrichment in organelles resembling acidocalcisomes, likely as PO₄³⁻, which may serve as a readily available energy source used over NO₃⁻ storage during the transition between aerobic and anaerobic respiration. Additionally, barium-rich vacuoles of unknown function(s) display a unique spatial distribution. This study emphasizes the effectiveness of cryogenic techniques in elucidating metabolic processes in foraminifers and other large and/or testate unicellular organisms, particularly for studying soluble compounds that have rarely been investigated.

Cercozoa = Filosa (Rhizaria, SAR) is one of the largest rhizarian subgroups and consists of a diverse assemblage of amoeboid and flagellated protists. They are ecologically significant in microbial food webs, widely diverse, and even abundant in soils and deep marine sediments according to environmental sequencing. In spite of this, the cercozoan phylogeny remains poorly resolved by SSU rRNA gene analysis, and omics data are available for only a few well-characterized species. Here, we have sequenced the transcriptomes of three new gliding monadofilosan strains: the glissomonad RAM19S6, the marimonad CRO19P5, and the discocelid GT001. Because of its unusual morphology, we performed a thorough morphological characterization of the strain GT001 using light and electron microscopy and described a new species, Discocelia plataet sp. n. Transmission electron microscopy and expansion microscopy revealed the structure of the flagellar apparatus, allowing us to identify cercozoan microtubular root homologies and supplement our knowledge of the discocelid cell structure with new details. Unique features of the new species are the absence of body tip and velum tip, discoidal mitochondrial cristae, and presence of an acronema on the posterior flagellum. We discuss the phylogenetic position of the three strains within Monadofilosa and the evolutionary context of the order Discocelida.

Plastids in almost all photosynthetic lineages originated from a primary endosymbiosis between cyanobacteria and heterotrophic eukaryotes in an ancestor of Archaeplastida. Strikingly, this event was repeated about a billion years later in an ancestor of photosynthetic Paulinella. Due to the recent and independent occurrence of this second primary endosymbiosis, Paulinella amoebae serve as a remarkable model group for studying the origin of plastids. To date, three species of photosynthetic Paulinella have been described mainly from freshwater and marine environments. Here, we describe a fourth photosynthetic Paulinella species from a brackish beach near Vancouver (British Columbia, Canada) using morphological and molecular data that we named Paulinella acadia sp. nov. Although P. acadia sp. nov. appears similar to P. chromatophora under light microscopy, scanning electron microscopy and molecular phylogenetic analyses demonstrate its close relationship to P. longichromatophora. The discovery of P. acadia sp. nov. expands the diversity and ecological range within this group. Notably, it is the second photosynthetic Paulinella species found on a beach to be described, alongside its sister P. longichromatophora.

Fachetti, B. S., M. Turiel-Silva, C. Wendt et al. 2025. “3D Electron Microscopy Reveals the Structural Complexity of the Intravacuolar Membranous Network in Cyrilia lignieresi-Infected Erythrocytes of the Fish Synbranchus marmoratus.” Journal of Eukaryotic Microbiology 72, no. 4: e70031. https://doi.org/10.1111/jeu.70031.

In the originally published article, author Brenda Santarém Fachetti's name was incorrectly given as Brenda Santarém Fachetii. This has been corrected in the online version of the article.

We apologize for this error.

Nanoplanktonic diatoms (2–20 μm) are a significant yet historically understudied component of marine ecosystems. We investigated three recently isolated nanoplanktonic diatoms from the Northwest Atlantic Ocean (NWA): Minidiscus spinulatus, Mediolabrus comicus, and Minidiscus trioculatus. Using Oxford Nanopore sequencing, we assembled and annotated their complete chloroplast and mitochondrial genomes. Pangenome analyses revealed that Minidiscus species consistently clustered more closely with select Thalassiosira species, whereas M. comicus formed a sister clade with Skeletonema. Circularized chloroplast genomes allowed us to characterize the full-length 16S ribosomal RNAs for each isolate, thereby leading to higher resolution of these taxa in preexisting 16S metabarcoding data. During our study, M. spinulatus was primarily restricted to the Bedford Basin. In contrast, both M. trioculatus and M. comicus had larger geographic ranges extending to the Labrador Sea, and in the case of M. comicus, to the Canadian Arctic Gateway. Weekly metabarcoding from the coastal Bedford Basin, N.S., Canada (2014–2022), revealed a seasonal succession of nanoplanktonic taxa, with Minidiscus trioculatus dominating in the early months, followed by M. comicus and M. spinulatus. Our results highlight the critical value of phytoplankton isolations and organelle genomics for expanding our understanding of the diversity and biogeography of nanoplanktonic diatoms.

The genus Acanthamoeba includes widespread protozoa that can cause severe infections in humans. Their ability to form resistant cysts within infected tissues complicates treatment, making it essential to understand the encystation process for developing effective therapeutic strategies. This study utilized untargeted metabolomics (GC–MS) to analyze metabolic changes during the encystation of an Acanthamoeba strain in Neff's encystation saline. We conducted metabolite analysis at three stages of differentiation: the trophozoite-dominant phase (0 h), the pre-cyst-dominant phase (24 h), and the cyst-dominant phase (72 h). The results indicated a global metabolic downregulation during encystation, which is consistent with a state of dormancy. Components of the cyst wall such as cellobiose and lactose accumulated in the final phase. Arbutin and canavanine were annotated for the first time in Acanthamoeba. Encystation also led to changes in pathways related to glycine, serine, and threonine metabolism and biosynthesis of aminoacyl-tRNA. This study uncovered previously unknown metabolites and metabolic pathways at distinct stages of Acanthamoeba development.