![]() (A) Essential membrane-bound Mam proteins (labeled with respective letters) (see also Table 1) are thought to tightly interact at the cytoplasmic membrane and eventually facilitate formation and growth of vesicles. ( 16) and others.įIG 1 FIG 1 Steps and some key proteins of magnetosome biogenesis. Therefore, much progress has been made in applied research on MTB and the use of magnetosomes, which has been reviewed, for example, by Vargas et al. Because of the precisely controlled, unique properties of magnetosomes, MTB have attracted interdisciplinary scientific attention for decades not only from microbiologists and biomedical researchers but also from physicists, materials scientists, geologists, paleontologists, and others. For example, the use of bacterial magnetosomes has been successfully tested in pilot applications such as magnetic imaging techniques like magnet resonance imaging and magnetic particle imaging ( 17) or magnetic hyperthermia ( 18, 19). Since the organelles can readily be isolated from disrupted cells, they can also be modified in vitro, and much of the interest in their biosynthesis has been motivated by their potential use in several biotechnical and biomedical settings. Moreover, the particular magnetosome envelope provides an excellent target to add artificial functions by genetic and biochemical coupling of diverse bioactive moieties such as fluorophores, enzymes, antibody fragments, or other ligands ( 15, 16). The precise control that is exerted during all stages of biomineralization yields magnetic nanoparticles with exceptionally well-defined characteristics such as high crystallinity, strong magnetization, and a uniform size distribution, mostly outcompeting technically produced magnetic nanocrystals ( 13, 14). This suggests that magnetosomes represent one of the most complex structures found in prokaryotic cells ( 11, 12). The number, size, shape, subcellular arrangement, and chemical composition of the magnetic crystals vary considerably between phylogenetic groups ( 4, 9, 10), reflecting a high diversity of biomineralization processes and adaptation to lifestyle, biotope, and cell morphology. This sensor is assumed to direct the swimming of MTB along magnetic field lines and vertical redox gradients within sediments or oxic-anoxic transition zones of natural waters ( 5 – 8). These bacteria all share the ability to form magnetosomes, which are organelles consisting of dedicated vesicles, each synthesizing a perfect crystal of a magnetic iron mineral that operates as part of a sensor for the Earth’s magnetic field. Today, 45 and 57 years later, respectively, much has been learned about this exceptional sense in what are now known as “magnetotactic bacteria” (MTB), which actually represent a phylogenetically diverse collection of single and multicellular bacteria that are abundant and widespread in almost any aquatic habitat ( 3, 4). In 1975, Richard Blakemore rediscovered what had been observed by Salvatore Bellini in 1963 as “a unique behavior of freshwater bacteria”: some of them seemed able to sense and swim along magnetic fields, apparently by use of magnetic iron minerals ( 1, 2). Finally, we discuss the impact of magnetotaxis on motility and its interconnection with chemotaxis, showing that magnetotactic bacteria are outstandingly adapted to lifestyle and habitat. First, we provide an overview on magnetosome vesicle synthesis and magnetite biomineralization, followed by a discussion of the perceptions of dynamic organelle positioning and its biological implications, which highlight that magnetotactic bacteria have evolved sophisticated mechanisms to construct, incorporate, and inherit a unique navigational device. In this minireview, we summarize new insights and place the molecular mechanisms of magnetosome formation in the context of the complex cell biology of Magnetospirillum spp. Recently, much has been revealed about the process of magnetosome biogenesis and dedicated structures for magnetosome dynamics and positioning, which suggest an unexpected cellular intricacy of these organisms. However, two of the genetically amenable Magnetospirillum species have emerged as tractable model organisms to study magnetosome formation and magnetotaxis. Most of these microorganisms cannot be cultivated under controlled conditions, much less genetically engineered, with only few exceptions. The source of this amazing trait is magnetosomes, unique organelles used to synthesize single nanometer-sized crystals of magnetic iron minerals that are queued up to build an intracellular compass. ![]() Magnetotactic bacteria are aquatic or sediment-dwelling microorganisms able to take advantage of the Earth’s magnetic field for directed motility. ![]()
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