Results 1 - 10 of 429
Results 1 - 10 of 429. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] A digital holographic microscope is employed to measure the 3D motion of free-swimming microorganisms. The focus function used to quantify image sharpness provides a better depth-directional accuracy with a smaller depth-of-focus compared with the intensity method in determining the depth-directional position of spherical particles of various diameters. The focus function is then applied to measure the 3D positions of free-swimming microorganisms, namely dinoflagellates C. polykrikoides and P. minimum. Both automatic segmentation and proper selection of a focus function for a selected segment are important processes in measuring the positional information of two free-swimming microorganisms of different shapes with various width-to-length ratios. The digital holographic microscopy technique improved in this work is useful for measuring 3D swimming trajectories, velocities and attitudes of hundreds of microorganisms simultaneously. It also exhibits exceptional depth-directional accuracy
[en] Several aspects of the biology and morphology of the toxic dinoflagellate Pyrodinium bahamense van compressum (Bohm) Steidinger, Tester and Taylor, have not yet been fully explored due to the limitations of the approaches so far utilized. Confocal Laser Scanning Microscopy (CLSM) coupled with differential staining technique has revealed new information that have not yet been reported. We present the development of a fast and reproducible sample preparation method that allows observation on the morphology of the organism during transformation from the vegetative to the pellicle cyst stages. Results have shown that bacterial endocytes are closely associated, with the chloroplasts in the algal vegetative cells which are thought to have implications on the survival of the organism. During pellicle encystment induced by changes in the laboratory conditions, extrusion of cytoplasmic materials and bacteria were observed. Laser micrographs reveal that the pellicle cyst body could be mainly composed of lipid globules and reduced forms of the chloroplast. Condensed genetic material, a characteristic of dinoflagellate cells, has also been observed in the pellicle cyst for the first time. Unlike in other dinoflagellate species, the pellicle wall of this organism is thin and irregular in shape. Also, we describe a hypothesis of a possible mechanism of bacterial horizontal transfer as a consequence of the development changes during reversal of the pellicle cyst to vegetative state. (author)
[en] Trypanosoma vivax is a haemoparasite affecting the livestock industry in South America and Africa. Despite the high economic relevance of the disease caused by T. vivax, little work has been done on its molecular characterization, in contrast with human trypanosomes, such as T. brucei and T. cruzi. The present study reports the construction of a semi-normalized genomic library and the sequencing of 160 Genome Sequence Survey (GSS) ends of T. vivax. The analyses of this preliminary data show that this simple and rapid approach worked well to generate some potential new markers for this species. (author)
[en] In the unicellular parasite Trypanosoma brucei, the causative agent of human African sleeping sickness, complex swimming behavior is driven by a flagellum laterally attached to the long and slender cell body. Using microfluidic assays, we demonstrated that T. brucei can penetrate through an orifice smaller than its maximum diameter. Efficient motility and penetration depend on active flagellar beating. To understand how active beating of the flagellum affects the cell body, we genetically engineered T. brucei to produce anucleate cytoplasts (zoids and minis) with different flagellar attachment configurations and different swimming behaviors. We used cryo-electron tomography (cryo-ET) to visualize zoids and minis vitrified in different motility states. Here, we showed that flagellar wave patterns reflective of their motility states are coupled to cytoskeleton deformation. Based on these observations, we propose a mechanism for how flagellum beating can deform the cell body via a flexible connection between the flagellar axoneme and the cell body. Lastly, this mechanism may be critical for T. brucei to disseminate in its host through size-limiting barriers.
[en] Highlights: ► Characterization of the proliferating cell nuclear antigen in Trypanosoma brucei (TbPCNA). ► TbPCNA is a suitable marker to detect replication in T. brucei. ► TbPCNA distribution and regulation is different compared to closely related parasites T. cruzi and Leishmania donovani. -- Abstract: As in most eukaryotic cells, replication is regulated by a conserved group of proteins in the early-diverged parasite Trypanosoma brucei. Only a few components of the replication machinery have been described in this parasite and regulation, sub-nuclear localization and timing of replication are not well understood. We characterized the proliferating cell nuclear antigen in T. brucei (TbPCNA) to establish a spatial and temporal marker for replication. Interestingly, PCNA distribution and regulation is different compared to the closely related parasites Trypanosoma cruzi and Leishmania donovani. TbPCNA foci are clearly detectable during S phase of the cell cycle but in contrast to T. cruzi they are not preferentially located at the nuclear periphery. Furthermore, PCNA seems to be degraded when cells enter G2 phase in T. brucei suggesting different modes of replication regulation or functions of PCNA in these closely related eukaryotes.
[en] Full text: Chagas disease remains a leading public health concern throughout much of Central and South America. Over 16 million people were infected with Trypanosoma cruzi, the causative agent of Chagas Disease, and further 100 million were at risk, prior to the initiation of the regional vector control initiatives. With neither a cure nor vaccine available, control relies heavily on strategies that eliminate the domestic triatomine vectors of T. cruzi. Insecticide-based strategies have had initial success but are limited by problems of cost, sustainability, and the inability to control non-domiciliated bug populations. Extra-domiciliary bug populations present the risk of re-invading human dwellings in the absence of continued use of chemicals. For the past 10 years, our group has developed a novel strategy to render bugs incapable of T. cruzi transmission. This approach, termed paratransgenesis, involves genetic manipulation of symbiotic bacteria resident in the gut lumen of the bug, to export molecules that are toxic to T. cruzi. Triatomines disperse the symbiotic bacteria to their progeny via fecal contamination. Nymphs that probe feces of adult bugs rapidly establish gut infections with the symbiont. We have exploited the biology of bacterial transfer amongst triatomines to create a synthetic paste termed CRUZIGARD for field delivery of engineered bacteria. Viewed as an integrated control strategy, this method would complement and ensure the sustainability of the ongoing insecticide-based initiatives. The strategy is designed to completely block transmission by targeting bug populations that prove resilient to conventional methods. The novel concept of the auto-propagation of a transmission-blocking agent is based on the natural and efficient dispersal of genetically altered bacteria through lateral spread of fecal material in bug colonies, making it cost-effective and sustainable. Significant barriers still exist to field use of this technology. The efficacy of the strategy remains to be tested under simulated field conditions to estimate its potential health impact. On the other hand, the environmental and ecological effects of CRUZIGARD exposure need to be characterised in order to develop a safe intervention. The stakeholders' overview and participation should also be an integral component of the research to develop a culturally acceptable control intervention. Socio-cultural, ethical and legal factors should be addressed in parallel to the technical advances. A communication strategy should be planned based on the public knowledge of disease burden, the perceived risks and benefits of the proposed strategy, and the influence of the media and other organised institutions on public debate and public health deliberations. The ethical aspects that need to be considered range from the individual to the community level: individual health risks to wide access to potential benefits. On the legal aspect, one of the major constraints, at the sites where this technology will be eventually applied, is the lack of local scientific steering committees and of the adequate regulatory framework. (author)
[en] A taxonomic survey of the dinoflagellate genus Ceratium Schrank was conducted on ten stations in the Grand-Lahou lagoon. A total of 27 species have been identified and described. Three species and one variety (Ceratium arietinum, Ceratium dens, Ceratium pulchellum and Ceratium furca var. Berghii) are new records for Cote d'Ivoire. (author)