RESUMO
Recent progress in understanding the early evolution of eukaryotes was tied to morphological identification of flagellates and heliozoans from natural samples, isolation of their culture and genomic and ultrastructural investigations. These protists are the smallest and least studied microbial eukaryotes but play an important role in the functioning of microbial food webs. Using light and electron microscopy, we have studied the diversity of heterotrophic flagellates and centrohelid heliozoans from marine waters of Curacao (The Netherlands Antilles), and provide micrographs and morphological descriptions of observed species. Among 86 flagellates and 3 centrohelids encountered in this survey, five heterotrophic flagellates and one Ñentrohelid heliozoan were not identified even to the genus. Some flagellate protists have a unique morphology, and may represent undescribed lineages of eukaryotes of high taxonomic rank. The vast majority (89%) of identified flagellates is characterized by wide geographical distribution and have been reported previously from all hemispheres and various climatic regions. More than half of the species were previously observed not only from marine, but also from freshwater habitats. The parameters of the species accumulation curve indicate that our species list obtained for the Curacao study sites is far from complete, and each new sample should yield new species.
Assuntos
Organismos Aquáticos/classificação , Biodiversidade , Eucariotos/classificação , Água do Mar/parasitologia , Organismos Aquáticos/ultraestrutura , Curaçao , Eucariotos/ultraestrutura , Microscopia Eletrônica de Transmissão , Especificidade da EspécieRESUMO
The fine structure of parasitic protozoa has been the subject of intense investigation with the use of electron microscopy. The recent development of atomic force microscopy (AFM) and all of the techniques associated with AFM has created new ways to further analyze the structure of cells. In this review, the various, presently-available modalities of AFM are discussed, as well as the results obtained in analysis of: (i) the structure of intact and detergent-extracted protozoa; (ii) the surface of infected cells; (iii) the structure of parasite macromolecules; (iv) the measurement of surface potential; and (v) force spectroscopy, the measurement of elasticity and ligand-receptor interactions.
Assuntos
Eucariotos/ultraestrutura , Microscopia de Força AtômicaRESUMO
Endocytosis is essential for eukaryotic cell survival and has been well characterized in mammal and yeast cells. Among protozoa it is also important for evading from host immune defenses and to support intense proliferation characteristic of some life cycle stages. Here we focused on the contribution of morphological and cytochemical studies to the understanding of endocytosis in Trichomonas, Giardia, Entamoeba, Plasmodium, and trypanosomatids, mainly Trypanosoma cruzi, and also Trypanosoma brucei and Leishmania.
Assuntos
Endocitose , Eucariotos , Animais , Entamoeba/metabolismo , Entamoeba/fisiologia , Entamoeba/ultraestrutura , Eucariotos/metabolismo , Eucariotos/fisiologia , Eucariotos/ultraestrutura , Giardia/metabolismo , Giardia/fisiologia , Giardia/ultraestrutura , Histocitoquímica , Leishmania/metabolismo , Leishmania/fisiologia , Leishmania/ultraestrutura , Microscopia Eletrônica , Plasmodium/metabolismo , Plasmodium/fisiologia , Plasmodium/ultraestrutura , Trichomonas/metabolismo , Trichomonas/fisiologia , Trichomonas/ultraestrutura , Trypanosoma brucei brucei/metabolismo , Trypanosoma brucei brucei/fisiologia , Trypanosoma brucei brucei/ultraestrutura , Trypanosoma cruzi/metabolismo , Trypanosoma cruzi/fisiologia , Trypanosoma cruzi/ultraestruturaRESUMO
This work is part of an ongoing investigation into the characteristics of Myxozoan parasites of freshwater fish in Brazil and was carried out using morphology, histopathology and molecular analysis. A new Myxosporea species (Myxobolus cordeiroi) is described infecting the jaú catfish (Zungaro jahu). Fifty jaú specimens were examined and 78% exhibited plasmodia of the parasite. The plasmodia were white and round, measuring 0.3-2.0mm in diameter and the development occurred in the gill arch, skin, serosa of the body cavity, urinary bladder and eye. The spores had an oval body and the spore wall was smooth. Partial sequencing of the 18S rDNA gene resulted in a total of 505bp and the alignment of the sequences obtained from samples in different organs revealed 100% identity. In the phylogenetic analysis, the Myxobolus species clustered into two clades-one primarily parasites of freshwater fish and the other primarily parasites of marine fish. M. cordeiroi n. sp. was clustered in a basal position in the freshwater fish species clade. The histological analysis revealed the parasite in the connective tissue of the different infected sites, thereby exhibiting affinity to this tissue. The plasmodium was surrounded by an outer collagen capsule of fibers with distinct orientation from the adjacent connective tissue and an inner layer composed of delicate collagen fibrils-more precisely reticular fibers. The development of the parasite in the cornea and urinary bladder caused considerable stretching of the epithelium.
Assuntos
Peixes-Gato/parasitologia , Eucariotos/classificação , Eucariotos/isolamento & purificação , Infecções Protozoárias em Animais/parasitologia , Animais , Brasil , Eucariotos/genética , Eucariotos/ultraestrutura , Doenças dos Peixes/parasitologia , Brânquias/parasitologia , Filogenia , Membrana Serosa/parasitologia , Pele/parasitologia , Esporos de Protozoários , Bexiga Urinária/parasitologiaRESUMO
Electron microscopy may be useful in chemotherapy studies at distinct levels, such as the identification of subcellular targets in the parasites and the elucidation of the ultimate drug mechanism of action, inferred by the alterations induced by antiparasitic compounds. In this review we present data obtained by electron microscopy approaches of different parasitic protozoa, such as Trypanosoma cruzi, Leishmania spp., Giardia lamblia and trichomonads, under the action of drugs, demonstrating that the cell architecture organization is only determined in detail at the ultrastructural level. The transmission electron microscopy may shed light (i.e. electrons) not only on the affected compartment, but also on the manner it is altered, which may indicate presumable target metabolic pathways as well as the actual toxic or lethal effects of a drug. Cytochemical and analytical techniques can provide valuable information on the composition of the altered cell compartment, permitting the bona fide identification of the drug target and a detailed understanding of the mechanism underneath its effect. Scanning electron microscopy permits the recognition of the drug-induced alterations on parasite surface and topography. Such observations may reveal cytokinetic dysfunctions or membrane lesions not detected by other approaches. In this context, electron microscopy techniques comprise valuable tools in chemotherapy studies.
Assuntos
Antiprotozoários/farmacologia , Eucariotos/efeitos dos fármacos , Microscopia Eletrônica/métodos , Animais , Sistemas de Liberação de Medicamentos , Eucariotos/ultraestrutura , Humanos , Infecções por Protozoários/tratamento farmacológico , Infecções por Protozoários/parasitologiaRESUMO
A hydrogenosome is a hydrogen-producing organelle, evolutionary related to mitochondria and is found in Parabasalia protozoa, certain chytrid fungi and certain ciliates. It displays similarities to and differences from mitochondria. Hydrogenosomes are spherical or slightly elongated organelles, although very elongated hydrogenosomes are also found. They measure from 200 nm to 1 microm, but under stress conditions can reach up to 2 microm. Hydrogenosomes are surrounded by two closely apposed membranes and present a granular matrix. Cardiolipin has been detected in their membranes, and frataxin, which is a conserved mitochondrial protein involved in iron metabolism, was also recently found. Hydrogenosomes have one or multiple peripheral vesicles, which incorporate calcium. The peripheral vesicle can be isolated from the hydrogenosomal matrix and can be considered as a distinct hydrogenosomal compartment. Dysfunctional hydrogenosomes can be removed by an autophagic process and further digested by lysosomes. Hydrogenosomes divide in three different ways, like mitochondria, by segmentation, partition and the heart form. They may divide at any phase of the cell cycle. Nucleoid or electron dense deposits found in hydrogenosomes can be considered artifacts or dysfunctional hydrogenosomes. The hydrogenosome does not contain a genome, although DNA has already been detected in one anaerobic ciliate. Hydrogenosomes can be considered as good drug targets since their metabolism is distinct from mitochondria.
Assuntos
Cilióforos/metabolismo , Eucariotos/metabolismo , Hidrogênio/metabolismo , Organelas/metabolismo , Animais , Cardiolipinas/metabolismo , Cilióforos/ultraestrutura , Vesículas Citoplasmáticas/metabolismo , Vesículas Citoplasmáticas/ultraestrutura , Eucariotos/ultraestrutura , Membranas Intracelulares/metabolismo , Membranas Intracelulares/ultraestrutura , Proteínas de Ligação ao Ferro/metabolismo , Mitocôndrias/metabolismo , Mitocôndrias/ultraestrutura , Organelas/ultraestrutura , FrataxinaRESUMO
As eukaryotic cells, protozoa present a classical structural organization where most of the structures and organelles typical of mammalian cells are found. However, even for usual organelles these organisms present structural diversity. In addition, some of the protozoa structures, such as the mitochondria, peroxisomes and even the Golgi complex, are not observed. On the other hand, new organelles such as the hydrogenosomes, mitosomes, Apicoplast, kinetoplast, glycosomes (specialized peroxisomes), rhoptries, micronemes and dense granules, are characteristic features of some protozoa. Also, several unusual cytoskeletal structures, some of them made of yet uncharacterized proteins, are seen in these eukaryotic microorganisms. Further characterization of these structures indicates that they contain special enzymes involved in distinct metabolic pathways making them potential targets for the development of new anti parasite drugs.
Assuntos
Eucariotos/ultraestrutura , Organelas/ultraestrutura , Animais , Antiprotozoários/farmacologia , Citoesqueleto/metabolismo , Citoesqueleto/ultraestrutura , Sistemas de Liberação de Medicamentos , Eucariotos/metabolismo , Organelas/metabolismoRESUMO
Parasitic protozoa such as Leishmania, Trypanosoma, Plasmodium, Toxoplasma gondii, Giardia and Trichomonas are able to cause several diseases affecting millions of people around the world with dramatic consequences to the socio-economic life of the affected countries. Diseases like malaria, leishmaniasis and trypanosomiasis have been classified by the World Health Organization as neglected diseases, because they have been almost completely forgotten by the governments as well as the pharmaceutical companies. The specific chemotherapy currently employed for the treatment of these diseases has serious limitations due to lack of efficacy, toxic side effects, growth of drug-resistance and high costs. Thus, it is urgent to develop new chemotherapeutic agents that are more effective, safe and accessible. In this context, several works have been focused on understanding the effect of different drug-treatments on these parasitic protozoa. Organelles and structures such as mitochondrion, kinetoplast, apicoplast, glycosome, acidocalcisome, hydrogenosome, plasma membrane and the cytoskeleton have been studied using different approaches to identify new targets for the development of new chemotherapeutic agents that are required. Some studies on alterations in the fine structure, as assayed using electron microscopy, have indicated the nature of lesions induced by several drugs, allowing deductions on possible modes of action. Here, we briefly review the available data of the effects of several drugs on the ultrastructure of parasitic protozoa and show how electron microscopy can contribute to elucidate the different mechanisms of these anti-parasitic drugs.
Assuntos
Antiprotozoários/farmacologia , Eucariotos/efeitos dos fármacos , Animais , Sistemas de Liberação de Medicamentos , Eucariotos/metabolismo , Eucariotos/ultraestrutura , Humanos , Microscopia Eletrônica/métodos , Organelas/efeitos dos fármacos , Organelas/metabolismo , Organelas/ultraestrutura , Infecções por Protozoários/tratamento farmacológicoRESUMO
Cell fractionation, a methodological strategy for obtaining purified organelle preparations, has been applied successfully to parasitic protozoa by a number of researchers. These studies have provided new information of the cell biology of these parasites and have supported investigators to assume that some of the protozoa form the roots of the evolutionary tree of eukaryotic cells. The cell fractionation usually starts with disruption of the plasma membrane, using conditions that minimize damage to the membranes bounding intracellular organelles. An important requirement for successful cell fractionation is the evaluation of the isolation procedure that can be made by morphological and biochemical methods. The morphological approaches use light and electron microscopy of thin section of different fractions obtained, and the biochemical methods are based on the quantification of marker enzymes or other molecules (for instance, a special type of lipid, an antigen, etc.). Here we will present our experience in the isolation and characterization of some structures found in trypanosomatids and trichomonads.