National Institute of Science and Technology for Structural Biology and Bioimaging

Transmission electron microscopy (TEM) is a key tool for the ultrastructural analysis of biological samples; however, it requires optimized fixation and contrast enhancement methods to achieve accurate results. Here, we evaluated the use of tannic acid as a mordant during primary fixation for TEM processing of Giardia intestinalis and Trichomonas vaginalis. When combined with osmium tetroxide (OsO4) post-fixation, tannic acid significantly improved in-block contrast in plasma membranes, organelle boundaries, and cytoskeletal elements, while preserving structural integrity. It increased electron density without introducing artifacts and, in some cases, allowed the omission of lead citrate staining, simplifying the protocol and reducing exposure to toxic agents. Even in the absence of OsO4, samples processed with tannic acid retained sufficient contrast to visualize basal bodies, axonemes, and other cytoskeletal filaments. Moreover, tannic acid enhanced the visualization of poorly characterized structures in the transition zone. We also demonstrate its successful use as a post-staining agent, replacing uranyl acetate for ultrathin sections while maintaining high image quality. These findings support tannic acid as a safe, cost-effective, and efficient alternative to traditional contrast agents, particularly under biosafety constraints, and contribute to the improvement of TEM protocols for studying protozoan morphology and cell biology.

Os resultados mostram que mesmo diante de um cenário político e econômico adverso, em 2022, 5,9% de todas as publicações científicas brasileiras trataram da covid-19, proporção superior à média mundial, que foi de 4,8%.

This work provides groundbreaking insights into the metabolic and evolutionary dynamics of endosymbiosis, a topic of central importance to cellular evolution. Angomonas deanei, a trypanosomatid species, has become a paradigm for investigating the evolution of eukaryotic cells and the origin of organelles through endosymbiosis. Harbored in the cytoplasm of this protozoan, the symbiont engages in intricate metabolic exchanges, offering a time window to analyze the processes and evolutionary history that underlie the establishment of permanent endosymbiotic relationships. By employing a multidisciplinary approach, we have uncovered how the symbiotic bacterium regulates the oxidative metabolism of the trypanosomatid, integrating glucose catabolism and optimizing energy production. Our discoveries have broad implications for understanding the metabolic integration of organelles, such as mitochondria and glycosomes, with the bacterial endosymbiont. Beyond unravelling the complexities of metabolic adaptations during symbiosis, our work may contribute to the general understanding of the evolutionary dynamics of parasitism within the Trypanosomatidae family.

Candida albicans is an opportunistic fungal pathogen that can cause superficial and life-threatening infections, particularly in immunocompromised individuals. Its ability to adhere to host cells is critical for colonization and infection. In this context, investigating ectophosphatases is particularly relevant, as these enzymes have been associated with fungal adhesion to host cells. This study aimed to investigate the nature of copper-induced stimulation of ectophosphatase activity in C. albicans. Ectophosphatase activity was measured using p-nitrophenyl phosphate as substrate. Micromolar concentrations of CuCl2 markedly stimulated ectophosphatase activity, and its response to reducing agents and metal chelators suggested that this modulation does not involve redox reactions. The significant differences between the biochemical properties of basal (Cu2+-independent) and Cu2+-dependent ectophosphatase activities suggest the presence of at least two distinct ectophosphatases in C. albicans. Cu2+-independent ectophosphatase activity presented an acidic profile and was insensitive to Mg2+, whereas Cu2+-dependent ectophosphatase activity exhibited an alkaline profile and was also stimulated by Mg2+. Both activities were negatively modulated by classical phosphatase inhibitors, but Cu2+-dependent ectophosphatase had lower sensitivity compared to the basal activity. These findings highlight the role of copper as a modulator of C. albicans ectophosphatase activity and suggest potential implications for fungal adaptation during infection.

Macromolecules are incorporated by eukaryotic cells through a process known as endocytosis, intensely analyzed in mammalian and yeast cells, but still lacking deep studies in pathogenic protists. Here we present what is presently known on endocytic activity carried out in some members of the Apicomplexa group (mainly concentrated in Plasmodium and Toxoplasma, but with references to Eimeria, Babesia, and Theileria). In most cells, endocytic activity takes place throughout the cell's surface. In apicomplexans, it is restricted to a special surface structure known as a micropore (also called cytostome). Recent studies indicate that several proteins are in the micropore, playing a role in macromolecule uptake from the medium via budding vesicles.

All insect trypanosomatids of the subfamily Strigomonadinae harbor a proteobacterial symbiont in their cytoplasm and unique ultrastructural cell organization. Here, we report an unexpected finding within the Strigomonadinae subfamily: the identification of a new species lacking bacterial symbiont, represented by two isolates obtained from Calliphoridae flies in Brazil and Uganda. This species is hereby designated as Kentomonas inusitatus n. sp. Molecular investigations targeting symbiont DNA, cell proliferation, and ultrastructural analyses agreed with the absence of bacterial symbionts in cultured flagellates. PCR-screening specifically targeting symbiont DNA corroborated the absence of symbionts in K. inusitatus present in the intestine of the respective host flies. K. inusitatus exhibited forms varying in size and shape. While displaying overall ultrastructural features of the Strigomonadinae, the novel species showed mitochondrial branches juxtaposed to the plasma membrane in locations both without and notable, with subpellicular microtubules. The discovery of the first Strigomonadinae species naturally lacking a symbiont and closely related to K. sorsogonicus, suggests a unique evolutionary history for the genus Kentomonas. Our findings provide novel insights into the complex relationships between trypanosomatids and their symbionts.