Henrique Lins de Barros

Simple homemade apparatus for harvesting uncultured magnetotactic microorganisms

Descrevemos um aparato simples para a captura de microrganismos magnetotacticos nao cultivados. Este aparato consiste em um recipiente de vidro com duas aberturas. Uma abertura maior na parte superior e usada para introduzir o sedimento e a agua. O sedimento e a agua sao previamente armazenados em um recipiente semitampado, previamente testado para a presenca de bacterias magnetotacticas. O aparato e exposto a um campo magnetico, devidamente alinhado, em uma bobina feita a mao e as bacterias sao removidas pela extremidade capilar da segunda abertura do recipiente. As bacterias coletadas podem entao ser usadas em estudos ultraestruturais usando a tecnica de imagem espectroscopica eletronica. Um grande numero de bacterias consistindo de cocos e bastonetes foi eficientemente coletado de diferentes ambientes. Este aparato e util para estudos microbiologicos sobre microrganismos magnetotacticos nao cultivaveis, especialmente em abordagens moleculares para investigacoes filogeneticas que fornecem informacoes sobre a diversidade natural de comunidades microbianas.

The observation of large magnetite (Fe3O4) crystals from magnetotactic bacteria by electron and atomic force microscopy

Magnetite crystals inside coccoid magnetotactic bacteria found in lagoons near Rio de Janeiro city were examined by electron microscopy (EM) and atomic force microscopy (AFM). For AFM, ultrathin sections of bacteria embedded in Epon resin were etched with an ethanolic NaOH solution and observed both in the height and in the force modes. Comparative electron microscope images were useful for identifying crystalline reliefs in the etched sections. Different situations representing particular arrangements of crystal chains were observed by AFM. The majority of the bacteria examined presented unusually large magnetite crystals which remained strongly attached in linear chains even after the laboratory procedures for their isolation. This behaviour is different from all other biogenic magnetite crystals isolated so far. It is suggested that this attachment is due to the strong field between individual crystals as well as to the contact areas, which are the largest observed until now. The correct identification of a particular topography by AFM as a crystal relief may be critical when crystals are not aligned in chains; in these cases the linear dimensions and the presence of well‐defined edges and faces are important features to be taken into account. Characterization of the crystal faces is important for the study of magnetotactic micro‐organisms since the crystalline habits seem to be species‐specific. Observation of etched sections proved to be a helpful approach for crystal relief observation, especially when small amounts of bacteria were available.

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.

Seasonal patterns in the orientation system of the migratory ant Pachycondyla marginata

Abstract. Route directions of migrations by the neotropical termite-hunting ant Pachycondyla marginata at a forest reserve in Southeast Brazil were analysed by circular statistic. Colony movement patterns were compared between the rainy/hot and dry/cold seasons. Migrations during the dry/cold season are significantly oriented 13° with the magnetic North–South axis, while rainy/hot migrations do not exhibit a preferred direction. This result is discussed considering the hypothesis that P. marginata ants may use the geomagnetic field as an orientation cue for migrations in the dry/cold season. The presence of magnetic iron oxides in the head and abdomen of P. marginata is consistent with this suggestion.

Magnetic properties of the microorganism Candidatus Magnetoglobus multicellularis

Magnetotactic microorganisms use the interaction of internal biomineralized nanoparticles with the geomagnetic field to orientate. The movement of the magnetotactic multicellular prokaryote Candidatus Magnetoglobus multicellularis under an applied magnetic field was observed. A method using digital image processing techniques was used to track the organism trajectory to simultaneously obtain its body radius, velocity, U-turn diameter, and the reorientation time. The magnetic moment was calculated using a self-consistent method. The distribution of magnetic moments and radii present two well-characterized peaks at (9 ± 2) × 10−15 and (20 ± 3) × 10−15 A m2 and (3.6 ± 0.1) and (4.3 ± 0.1) μm, respectively. For the first time, simultaneous determination of the distribution of the organism radii and magnetic moment was obtained from the U-turn method by a new digital imaging processing. The bimodal distributions support an organism reproduction process model based on electron microscopy observations. These results corroborate the prokaryote multicellular hypothesis for Candidatus M. multicellularis.

A study of magnetic properties of magnetotactic bacteria.

The first direct measurements of magnetic properties of magnetotactic bacteria from natural samples are presented. Measurements were made at 4.2 K, using a Superconducting Quantum Interfering Device (SQUID) magnetometer. From the magnetization results an anisotropy is obtained that is typical of magnetized ferro- or ferri-magnetic materials. The average magnetic moment of the bacteria determined from the results is in good agreement with the estimated moment from electron microscopy.

Biomineralization of a New Material by a Magnetotactic Microorganism

Magnetotactic bacteria were first observed by R.Blakemore when studying water sediments collected in Woods Hole (Massachusetts, USA)1. After his experimental work it was found that magnetotaxis is an orientation mechanism common to a large population of microorganisms and magnetotactic cells orient in a magnetic field, showing that the cell possesses a permanent magnetic dipole. 2 This experimental evidence suggests that the magnetic detector of such organisms is composed of minerals with permanent magnetization. Electron transmission microscopy of magnetotactic cells shows the presence of electron-dense regions with dimensions ranging from 400 to 1.500nm and geometric shapes. Until now all magnetotactic bacteria analysed present small crystals of Fe3O4, sometimes in an ordered distribution in the interior of the cell. The identification of magnetite in the cell cytoplasm was first made using Mossbauer spectroscopy on samples of Aquaspirillum magnetotacticum but Fe3O4 was later found in several other species of magnetotactic bacteria. Electron microscopy studies show evidence that crystals of Fe3O4 are enveloped by a membrane forming the magnetosome, a specialized organelle common to all magnetotactic cells 3–7.

Magnetotactic Microorganisms Found in Muds from Rio de Janeiro

Among the many mechanisms used by living beings to secure information from the environment in the pursuit of survival, the perception of the geomagnetic field plays a unique role. Weak, as compared to fields produced in the laboratory, but ever present, the geomagnetic field leaves behind records of its history in sediments, volcanic rocks, ceramic, etc., and alters important characteristics of the biosphere. Present throughout the entire process of the formation of species, its influence may be an important factor for the understanding of the behavior of living organisms.

Magnetic Orientation in Solenopsis sp. Ants

It is known that magnetic fields affect ants behavior. It has been shown that Solenopsis ants are sensitive to magnetic fields but there is no experimental evidence for magnetic orientation. In this paper experiments were done to verify the magnetic orientation of Solenopsis sp. ants. The spontaneous orientation of ants in a circular arena was studied in two different magnetic conditions: in the natural geomagnetic field and under an altered magnetic field, with the horizontal geomagnetic axis shifted in 90 º. Our results show that ants consistently change their orientation direction when the magnetic field was altered. Axial circular statistics analysis showed that, in the absence of other cues, ants orient spontaneously to the horizontal geomagnetic field axis. The present paper shows for the first time magnetic orientation in Solenopsis sp. ants.

Magnetic configuration model for the multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis

Candidatus Magnetoglobus multicellularis (CMm) is a multicellular organism in which each constituent cell is a magnetotactic bacterium. It has been observed that disaggregation of this organism provokes the death of the individual cells. The observed flagellar movement of the CMm indicates that the constituent cells move in a coordinated way, indicating a strong correlation between them and showing that this aggregate could be considered as an individual. As every constituent cell is a magnetotactic bacterium, every cell contributes with a magnetic moment vector to the resultant magnetic moment of the CMm organism that can be calculated through the vectorial sum of all the constituent magnetic moments. Scanning electron microscopy images of CMm organisms have shown that the constituent cells are distributed on a helix convoluted on a spherical surface. To analyze the magnetic properties of the distribution of magnetic moments on this curve, we calculated the magnetic energy numerically as well as the vectorial sum of the magnetic moment distribution as a function of the number of cells, the sphere radius and the number of spiral loops. This distribution proposes a magnetic organization not seen in any other living organism and shows that minimum energy configurations of magnetic moments are in spherical meridian chains, perpendicular to the helix turns. We observed that CMm has a high theoretical degree of magnetic optimization, showing that its geometrical structure is important to the magnetic response. Our results indicate that the helical structure must have magnetic significance.