Journal of Eukaryotic Microbiology最新文献

The endoplasmic reticulum (ER) is a large and highly dynamic component of the eukaryotic endomembrane system. In eukaryotic microalgae, it plays six distinct roles: (1) It envelopes the chromatin to form the nucleus. (2) It forms cisternae in the cytoplasm, some of which scaffold the synthesis of proteins destined for incorporation into membranes or for secretion. (3) It associates with Golgi cisternae to scaffold the synthesis of glycosylated proteins. (4) It associates with the plasma membrane to mediate the synthesis and secretion of hydrophobic molecules. (5) It mediates the synthesis of cytoplasmic lipid bodies. (6) In lineages harboring complex plastids of red algal ancestry, it forms the chloroplast ER, which envelops the primary chloroplast envelope. In this review, these systems are illustrated using the quick-freeze deep-etch electron microscopy (QFDEEM) technique, which lifts up the topological configurations adopted by this gossamer system. A key finding is that in all the complex microalgae examined except dinoflagellates, the inner nuclear envelope membrane associates directly with the plastid-contiguous membrane of the chloroplast ER at foci designated as chloroplast-nuclear junctions. These junctions may play a role in regulating the maintenance and physiology of the complex organelles.

This study employs advanced three-dimensional electron microscopy techniques, including Transmission Electron Microscopy (TEM) tomography and freeze-fracture imaging via scanning electron microscopy (SEM), to investigate the ultrastructural organization of Cyrilia lignieresi-infected red blood cells (iRBCs) in the host fish Synbranchus marmoratus. The analysis focuses on the parasitophorous vacuole (PV) and reveals a highly complex intravacuolar membranous network (IVN) composed of vesicles, tubules, and interconnected membranous structures. These elements exhibit considerable diversity in size, morphology, and electron density, suggesting dynamic functional roles in the parasite–host interaction. The electron tomography and three-dimensional reconstructions data provide unprecedented insights into the spatial organization and potential functional significance of these membranous systems. These findings not only enhance our understanding of the cellular adaptations of C. lignieresi but also contribute to a broader knowledge of apicomplexan parasitism and host–pathogen interactions.

Chagas disease, caused by the protozoan Trypanosoma cruzi, is a major neglected disease in Latin America. The amastigote, the replicative intracellular form, is essential for infection persistence in vertebrate hosts. These forms exhibit remarkable adaptability, modulating metabolism and growth according to host cell resource availability. Lipid metabolism plays a critical role in amastigote development, with a strong dependence on host-derived lipids, particularly cholesterol. Although T. cruzi can synthesize some sterols and fatty acids, it also scavenges essential lipids from the host. Changes in host cholesterol metabolism, possibly via SREBPs, may increase intracellular cholesterol levels and promote parasite growth. However, the mechanisms of cholesterol acquisition by amastigotes remain unclear. Here, we investigated cholesterol trafficking from host cells to amastigotes using a fluorescent cholesterol analog. Through confocal and volume electron microscopy, we demonstrated cholesterol uptake by amastigotes, characterized uptake kinetics, and confirmed its importance for parasite development. We also revealed close contact between the host endoplasmic reticulum and the amastigote plasma membrane, consistent with membrane contact sites. Furthermore, we showed that amastigotes can internalize ER- and Golgi-derived host markers, suggesting a potential route for acquisition of host molecules. These findings provide new insights into lipid acquisition strategies by intracellular T. cruzi amastigotes.

Drachko, D., and V. V. Zlatogursky. 2025. “Morphology, Systematics and Life Cycle of Ozanamia fimbriatus (Haptista: Centroplasthelida), With Notes on Evolution of Organic Skeleton in Centrohelids.” Journal of Eukaryotic Microbiology 72, no. 4: e70022. https://doi.org/10.1111/jeu.70022.

In the originally published article, the funding information given at the beginning of the article was incorrect. The correct funding information is given below. This has been updated in the online version of the article.

Incorrect

Funding: This work was supported by Russian Academy of Sciences, 24-74-10031.

Correct

Funding: This work was supported by the Russian Science Foundation, 24-74-10031.

We apologize for this error.

Tintinnid ciliates are distinguished by their loricae (shells), the key synapomorphy of these mainly marine planktonic protists. They can divide daily, with a considerable portion of biomass stored in the loricae. During each division, lorica-forming material (LFM) is produced and afterwards used by the proter (anterior division product) to construct a new lorica, while the opisthe (posterior division product) retains the parental one. Many aspects of lorica formation remain unclear, and no study describes the entire process from material maturation via secretion to assembly. Here, we present the first thorough investigation at cellular and sub-cellular levels, employing light microscopy on dividers and postdividers, as well as transmission electron microscopy on primarily cryofixed specimens from a Schmidingerella culture. Our study reconstructs LFM maturation, identifying two main developmental stages: the morula-shaped precursor granules and the mature granules. The latter cluster in the proter's ventral portion with a peripheral longitudinal strip of small granules embedded in large ones. Ultrastructurally and chemically, the mature granules of both size classes are identical. Through detailed live observations, we followed and documented, for the first time, the process of cell division, the behavior of the proter, the release of LFM granules, and features of lorica formation.

The nuclear genome is essential for encoding most of the genes required for cellular processes, but its size alone can alter the characteristics of cells and organisms. Yet, genome size variation and its ecological and evolutionary impacts, particularly in microorganisms, are not well understood. We used flow cytometry to estimate genome size and GC content in 53 evolutionary lineages of the microalgal genus Synura (Chrysophyceae, Stramenopiles). Genome size evolution was reconstructed in a phylogenetic framework using molecular markers. A set of genomic, morphological, and ecogeographic variables characterizing Synura lineages was evaluated and tested as predictors of genome size variation in phylogeny-corrected statistical models. Both genome size and GC content varied widely in Synura, ranging from 0.19 to 3.70 pg of DNA and 34.0% to 49.3%, respectively. Genome size variation was mainly associated with cell size, less with silica scale size, and not with scale ultrastructure. Higher soil nitrogen, higher latitudes, and lower temperatures correlated with larger genomes. Genome size evolution in Synura shows potential dynamism, with increases confined to short terminal branches, indicating lower macroevolutionary stability. Lineages with larger genomes exhibited a narrower range of suitable ecological conditions, possibly due to selection acting deleteriously against larger genomes (and cells).