Freeze-fracture study of the dynamics of Toxoplasma gondii parasitophorous vacuole development

7 p. : il.oxoplasma gondii resides in a nonfusogenic parasitophorous vacuole (PV), which provides a safe environment for parasite survival and replication. In this work, we used the freeze-fracture technique to analyze the PV during different times of T. gondii infection in an epithelial cell line. After a short time of interaction with host cell, T. gondii PV membrane already showed a significant quantity of intramembranous particles (IMPs)—293 IMPs/mm2. The IMP density evaluated did not vary until 6 h of interaction. As the PVarea enlarged with the progression of infection, the density of these particles increased, reaching a stable quantity in the order of 1100 particles/mm2. The IMPs were heterogeneous in size and were found distributed without any special pattern throughout the time of infection studied. The membrane lining the PV presented circular figures, which resembled vesicle fusion areas or attachments of the membranous tubular network, regions free from particles and small depressions, demonstrating to be a dynamic structure. IMPs were found in tubulo-vesicular structures present in the intravacuolar matrix, although rarely observed in elements of the intravacuolar network

New details on the fine structure of the rhoptry of Toxoplasma gondii

7 p. : il.Rhoptries are organelles that have important, complex roles in Apicomplexa biology. During Toxoplasma gondii infection, these organelles take part in several essential and complex processes that include host cell entry and parasite development. Using different electron microscopy techniques, we characterized the fine morphology of the rhoptries of two of the most important life stages of T. gondii: the tachyzoite and the bradyzoite forms. The observed tachyzoite and bradyzoite rhoptries had delimited regions characterized by a dark and electron-dense neck, an amorphous and less electron-dense bulb, and a region of intermediate electron density, which connects the bulb to the neck. Metal replicas of frozen-fractured tachyzoites showed intramembranous particles of different densities and sizes on the fractured faces of rhoptry membranes. Both in tachyzoites and bradyzoites, the intramembranous particles were arranged in distinctive parallel arrays that decorated most part of these organelles. Tubulo-vesicular subcompartments and free particles within the rhoptry lumen were observed on freeze-fractured replicas. Cryo-fixed, deepetched samples showed several pore-like structures localized in the bulb portion. No obvious evidence was found of a possible connection between rhoptries and micronemes

Organização estrutural do taquizoíto de Toxoplasma gondii

13 p. : il.Objetivos: fazer uma revisão dos aspectos básicos da ultraestrutura do taquizoíto de Toxoplasma gondii, agente etiológico da toxoplasmose. Fonte de dados: os dados apresentados tomam como referência resultados recentes obtidos pelos principais grupos de pesquisadores no mundo, que se dedicam ao estudo do Toxoplasma gondii, incluindo-se dados do próprio grupo de autores. Síntese dos dados: os taquizoítos de Toxoplasma gondii são responsáveis pela fase aguda da infecção, penetrando ativamente, através do complexo apical, em células dos hospedeiros onde se multiplicam. São abordadas características ultraestruturais e moleculares particulares da película, do citoesqueleto, de organelas secretórias (róptrias, micronemas e grânulos densos) e não secretórias (apicoplasto) exclusivas do filo Apicomplexa, além das peculiaridades do núcleo, mitocôndria, acidocalcisomas, retículo endoplasmático e complexo de Golgi desses parasitos intracelulares. Conclusões: estas características confirmam que o sucesso nas etapas de adesão, invasão e multiplicação do parasito possui clara correlação com suas características morfofuncionais. ____________________________________________________________________________________.ABSTRACT: To review basic aspects on the ultrastructure of the tachyzoite of Toxoplasma gondii, the causative agent of toxoplasmosis. Source of data: The data presented are based on recent publications by the most distinguished research groups in the area dedicated to the study of Toxoplasma gondii, including studies from the present authors. Summary of findings: The tachyzoites are responsible for the acute phase of the infection by actively penetrating, through the parasites’ apical complex, the host cells where they multiply. Both ultrastructural and molecular particularities of the pellicle, the cytoskeleton, secretory (rhoptries, micronemas and dense granules) and non secretory (apicoplast) organelles, specific to Apicomplexa phylum, besides peculiar features of the nucleus, mitochondrion, acidocalcisomes, endoplasmic reticulum and Golgi complex of these intracellular parasites. Conclusions: These characteristics confirm that the success in the process of adhesion, invasion and multiplication of this parasite is clearly correlated to its morphology

Thiolactomycin analogues as potential anti-Toxoplasma gondii agents

5 p. : il.The discovery of new compounds active against Toxoplasma gondii is extremely important due to the severe disease caused by this pathogen in immunocompromised hosts and to congenital infection. Type II fatty acid biosynthesis has shown to be a promising target for drug intervention in toxoplasmosis. Here we describe the inhibitory effect of 8 thiolactomycin (TLM) analogues against tachyzoite-infected LLC-MK2 cells. The TLM analogues demonstrated anti-T. gondii activity, arresting tachyzoite proliferation with IC50 values in the micromolar level after 24 h and 48 h of treatment. Metabolic labelling of extracellular parasites treated with TLM analogues using [3H]acetate demonstrated that these drugs affected acylglycerol synthesis. The rapid reduction of parasite load suggests that these compounds have selective cytotoxic effects against T. gondii. Transmission electron microscopy demonstrated that TLM analogues interfered with membrane-bounded organelles and parasite division and this in turn affected parasite development and survival

The redox potential interferes with the expression of laminin binding molecules in Bacteroides fragilis

The Bacteroides fragilis ATCC strain was grown in a synthetic media with contrasting redox potential (Eh) levels [reduced (-60 mV) or oxidised (+100mV)] and their adhesion capacity to extracellular matrix components was evaluated. The strain was capable of adhering to laminin, fibronectin, fibronectin + heparan sulphate and heparan sulphate. A stronger adherence to laminin after growing the strain under oxidising conditions was verified. Electron microscopy using ruthenium red showed a heterogeneous population under this condition. Dot-blotting analyses confirmed stronger laminin recognition by outer membrane proteins of cells cultured at a higher Eh. Using a laminin affinity column, several putative laminin binding proteins obtained from the cultures kept under oxidising (60 kDa, 36 kDa, 25 kDa and 15 kDa) and reducing (60 kDa) conditions could be detected. Our results show that the expression of B. fragilis surface components that recognise laminin are influenced by Eh variations