Juliana L. Martins

Structure, Behavior, Ecology and Diversity of Multicellular Magnetotactic Prokaryotes

Multicellular magnetotactic prokaryotes (MMPs) show a spherical morphology and are composed of 15–45 cells organized around an internal acellular compartment. Each cell presents a pyramidal shape with the apex of the pyramid facing this compartment The base, where the flagella are attached, faces the environment. MMPs display either a straight or a helical trajectory, and the sense of rotation of the trajectory (clockwise) is the same as the rotation of the microorganisms body during swimming. This is different to what would be expected if the flagella formed a bundle. The fact that MMPs present non-uniform velocities during “ping-pong movement” or “escape motility” further confirms the need for complex coordination of the action of flagella. The organisms express an unusual life cycle. Each organism grows by enlarging the cell volume, not the cell number; then, the number of cells doubles, the organism elongates, then it becomes eight-shaped, and finally splits into two equal spherical organisms. Most multicellular magnetotactic prokaryotes produce greigite (Fe3S4) magnetosomes, whereas recent observations show that these organisms can also biomineralize magnetite (Fe3O4). All data available on MMPs indicate that they constitute an important model for studies on multicellularity, biomineralization, and evolution in prokaryotes.

Antileishmanial activity of MDL 28170, a potent calpain inhibitor

Abstract Several calpain inhibitors are under development and some are useful agents against important human pathogens. We therefore investigated the effect of MDL 28170, a potent calpain inhibitor, on the growth of Leishmania amazonensis. After 48h of treatment, the inhibitor exhibited a dose-dependent antileishmanial activity, with a 50% lethal dose (LD50) of 23.3μM. The inhibitor promoted cellular alterations, such as the parasites becoming short and round. A calpain-like protein migrating at 80kDa was identified by Western blotting. In addition, the calpain-like molecules were identified on the cell surface of the flagellate. These results add new in vitro insights into the exploitation of calpain inhibitors in treating parasitic infections and add this family of peptidases to the list of potential targets for development of more potent and specific inhibitors against trypanosomatids.

Spatiotemporal distribution of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis in a Brazilian hypersaline lagoon and in microcosms

Candidatus Magnetoglobus multicellularis is an unusual morphotype of magnetotactic prokaryotes. These microorganisms are composed of a spherical assemblage of gram-negative prokaryotic cells capable of swimming as a unit aligned along a magnetic field. While they occur in many aquatic habitats around the world, high numbers of Ca. M. multicellularis have been detected in Araruama Lagoon, a large hypersaline lagoon near the city of Rio de Janeiro, in Brazil. Here, we report on the spatiotemporal distribution of one such population in sediments of Araruama Lagoon, including its annual distribution and its abundance compared with the total bacterial community. In microcosm experiments, Ca. M. multicellularis was unable to survive for more than 45 days: the population density gradually decreased coinciding with a shift to the upper layers of the sediment. Nonetheless, Ca. M. multicellularis was detected throughout the year in all sites studied. Changes in the population density seemed to be related to the input of organic matter as well as to salinity. The population density of Ca. M. multicellularis did not correlate with the total bacterial counts; instead, changes in the microbial community structure altered their counts in the environment.

Deep-Etching Electron Microscopy of Cells of Magnetospirillum magnetotacticum: Evidence for Filamentous Structures Connecting the Magnetosome Chain to the Cell Surface

Magnetospirillum magnetotacticum are magnetotactic bacteria that form a single chain of magnetite magnetosomes within its cytoplasm. Here, we studied the ultrastructure of M. magnetotacticum by freeze-fracture and deep-etching to understand the spatial correlation between the magnetosome chain and the cell envelope and its possible implications for magnetotaxis. Magnetosomes were found mainly near the cell envelope, forming chains that were closely associated with the granular cytoplasmic material. The membrane surrounding the magnetosomes could be visualized in deep-etching preparations. Thin connections between magnetosome chains and the cell envelope were observed in deep-etching images. These results strengthen the hypothesis for the existence of structures that transfer the torque from the magnetosome chains to the whole cell during the orientation of magnetotactic bacteria to a magnetic field lines.

A fotografia e seus duplos: um quadro na parede

Hans Belting suggests that ‘images are the nomads of media’ because they set up and dismantle their camps every time new media appear. Whenever photography portrays another image (painting, TV screen) it plays out a chapter in this history. Photography has been the guardian of the paradoxes in the distance and tensions between image and world in modern times. This is why it now holds a central position in the debate about contemporary visuality. Our fate and the fate of images are somehow interconnected. The last generation of visual artists from the twentieth century sought to express the pain of virtualization; twenty-first century photography is rediscovering the promise of a latent body in each image.

La tierra prometida de las imágenes

Since its invention, photography has increasingly occupied the place —necessarily and problematically— of the guardian of disparate images in a disenchanted world. It has monitored this distance —the distance between the image that verifies and another that eludes, between the transparency and opacity of the world—, for example, every time it includes a picture from another medium in it (a painting, a TV screen). Each one of these images stages a chapter in the history of photography in the 20th century. Its last generation of visual artists sought to express the pain of their own virtualization. The very first art ist of the new millennium rediscovered a latent promise of the body that lies inside every image.