Magnetotactic Bacteria and Magnetosomes

As stated in an Chapter 4, prokaryotes of both Domains or Superkingdoms, the Bacteria and the Archaea, mediate the formation of a large number of diverse minerals. They are known to do this either through biologically induced mineralization (BIM) (Lowenstam 1981) (the subject of Chapter 4 in this volume; Frankel and Bazylinski 2003) or biologically controlled mineralization (BCM). The latter has also been referred to as organic matrix-mediated mineralization (Lowenstam 1981) and boundary-organized biomineralization (Mann 1986). There are several important differences between BIM and BCM that will be discussed in detail in this chapter, most notably those dealing with aspects of the mineral crystals and the biomineralization process (see also Weiner and Dove 2003). However, there is another significant difference between the two modes of biomineralization and this is the aspect of functionality. Generally, in BIM there is no function to the biomineralized particles except, perhaps, as a solid substrate for attachment in the case of bacteria or as a form of protection against certain environmental conditions or attack from predators. However, it is easier to recognize the primary function of bone or shells produced by molluscs; two well-characterized examples of BCM by higher organisms. Functionality should always be examined when dealing with examples of biomineralization particularly in situations where the mineral product displays some qualities of both BIM and BCM.

In BCM, the organism exerts a great degree of crystallochemical control over the nucleation and growth of the mineral particles. For the most part, the minerals are directly synthesized at a specific location within or on the cell and only under certain conditions. The mineral particles produced by bacteria in BCM are characterized as well-ordered crystals with narrow size distributions, and specific, consistent particle morphologies. Because of these features, BCM processes are likely to be under specific chemical/biochemical and …

Biologically Controlled Mineralization in Prokaryotes

Biomimetic magnetic nanoparticles

This chapter examines and reviews features of biologically induced mineralization (BIM)- and biologically controlled mineralization (BCM)-type magnetic particles. It describes microorganisms that produce magnetic minerals (focusing mainly on the magnetotactic bacteria) and also describes the biomineralization processes involved in the synthesis of magnetic minerals. The chapter also reviews the physics and function of magnetotaxis in light of recent findings. In the microbial world, the most widely recognized example of BCM is magnetosome production by the magnetotactic bacteria. Although all freshwater magnetotactic bacteria synthesize magnetite as the mineral phase of their magnetsomes, many marine, estuarine, and salt marsh species produce an iron sulfide-type magnetosome which consists primarily of the magnetic iron sulfide greigite. The chapter discusses stoichiometry changes and specifically whether iron can be replaced with other transition metal ions and whether sulfur and oxygen can replace each other as the nonmetal component in the magnetosome mineral phase. The fact that many higher creatures biomineralize single-magnetic-domain magnetite crystals of similar morphologies suggests the intriguing idea that all these organisms have the same or a similar set of genes responsible for magnetite biomineralization that would probably have originated in the magnetotactic bacteria. Thus, studying how magnetotactic bacteria biomineralize magnetite might have a scientific impact far beyond the studies of microbiology and geology.

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Biologically Controlled Mineralization of Magnetic Iron Minerals by Magnetotactic Bacteria

Traditionally, auscultation is applied to the diagnosis of either respiratory disturbances by respiratory sounds or cardiac disturbances by cardiac sounds. In addition, for sleep apnea syndrome diagnosis, snoring sounds are also monitored. The present study was aimed at synchronous detection of all three sound components (cardiac, respiratory, and snoring) from a single spot. The sounds were analyzed with respect to the cardiorespiratory activity, and to the detection and classification of apneas. Sound signals from 30 subjects including 10 apnea patients were detected by means of a microphone connected to a chestpiece which was applied to the heart region. The complex nature of the signal was investigated using time, spectral, and statistical approaches, in connection with self-defined time-based and event-based characteristics. The results show that the obstruction is accompanied by an increase of statistically relevant spectral components in the range of 300 to 2000 Hz, however, not within the range up to 300 Hz. Signal properties are discussed with respect to different breathing types, as well as to the presence and the type of apneas. Principal component analysis of the event-based characteristics shows significant properties of the sound signal with respect to different types of apneas and different patient groups, respectively. The analysis reflects apneas with an obstructive segment and those with a central segment. In addition, aiming for an optimum detection of all three sound components, alternative regions on the thorax and on the neck were investigated on two subjects. The results suggest that the right thorax region in the seventh intercostal space and the neck are optimal regions. It is concluded that for patient assessment, extensive acoustic analysis offers a reduction in the number of required sensor components, especially with respect to compact home monitoring of apneas.

Acoustical signal properties for cardiac/respiratory activity and apneas

Main domains and surface domains in amorphous soft magnetic materials

For nondestructive domain analyses of transformer sheets with stress coating, high voltage SEM techniques as well as special colloid techniques have been developed. In the present study, a medium containing magnetotactic bacteria was applied to the sample surface. It was found that the bacteria orient themselves in the stray fields originating from the domain structure, and swim in the field direction. This allows visualization of domains whose stray field is directed into the sheet. Comparisons between the bacteria technique, colloid technique and computer controlled field scanning method are discussed for different kinds of materials.

https://iopscience.iop.org/article/10.1088/0031-8949/40/4/016/pdf

Why not use magnetotactic bacteria for domain analyses

The reliability of electric plethysmography for respiration monitoring is reduced by artefacts caused by the cardiac activity, by motions, electromagnetic cross-talk and others. For artefact suppression, a constant-current field-plethysmography technique is discussed which uses the voltage of an auxiliary electrode in addition to the conventional four-electrode arrangement. By means of a differential amplifier, a respiration signal is produced which is almost entirely free from heart artefacts, while the intensity of additional artefacts is suppressed. In principle, the technique can also be used for the separate determination of the ventilation intensity of the two lungs.

A method for the elimination of artefacts in electric field plethysmography of the lung.

On the effectiveness of magnetotactic bacteria for visualizations of magnetic domains

Recently, we reported the possibility to apply magnetotactic bacteria for domain studies.1 The high field sensitivity (≊30 A/m) yields effective orientations in the stray field of domains and thus their visualization. Here, we discuss fundamental aspects of broader applications including the collection of bacteria. For it, by means of numerical analysis, a magnetic trap was developed in order to guide bacteria in concentration vessels. With respect to the low active velocity (100 μm/s), also possibilities of passive guidance by means of gradient fields were studied, which, however, yielded minimum intensities of more than 1 kA/m. Roughly, this is consistent with results of susceptibility measurements showing magnetic moments of only 10−14 Am2 for bacteria of 1 μm diameter. Still, passive guidance could enable rapid concentration and translocation procedures, e.g., using the bacterium as a drug carrier. Future applications could include the use of genetically manipulated bacteria in biotechnology. As a pil...

K. Futschik

Papers

Main domains and surface domains in amorphous soft magnetic materials

Why not use magnetotactic bacteria for domain analyses

A method for the elimination of artefacts in electric field plethysmography of the lung.

On the effectiveness of magnetotactic bacteria for visualizations of magnetic domains

Fundamental aspects of practical applications of magnetotactic bacteria (abstract)