Magnetotactic bacteria

About: Magnetotactic bacteria is a research topic. Over the lifetime, 1118 publications have been published within this topic receiving 43741 citations.

Single-step production of a recyclable nanobiocatalyst for organophosphate pesticides biodegradation using functionalized bacterial magnetosomes.

Abstract: Enzymes are versatile catalysts in laboratories and on an industrial scale; improving their immobilization would be beneficial to broadening their applicability and ensuring their (re)use. Lipid-coated nano-magnets produced by magnetotactic bacteria are suitable for a universally applicable single-step method of enzyme immobilization. By genetically functionalizing the membrane surrounding these magnetite particles with a phosphohydrolase, we engineered an easy-to-purify, robust and recyclable biocatalyst to degrade ethyl-paraoxon, a commonly used pesticide. For this, we genetically fused the opd gene from Flavobacterium sp. ATCC 27551 encoding a paraoxonase to mamC, an abundant protein of the magnetosome membrane in Magnetospirillum magneticum AMB-1. The MamC protein acts as an anchor for the paraoxonase to the magnetosome surface, thus producing magnetic nanoparticles displaying phosphohydrolase activity. Magnetosomes functionalized with Opd were easily recovered from genetically modified AMB-1 cells: after cellular disruption with a French press, the magnetic nanoparticles are purified using a commercially available magnetic separation system. The catalytic properties of the immobilized Opd were measured on ethyl-paraoxon hydrolysis: they are comparable with the purified enzyme, with Km (and kcat) values of 58 µM (and 178 s−1) and 43 µM (and 314 s−1) for the immobilized and purified enzyme respectively. The Opd, a metalloenzyme requiring a zinc cofactor, is thus properly matured in AMB-1. The recycling of the functionalized magnetosomes was investigated and their catalytic activity proved to be stable over repeated use for pesticide degradation. In this study, we demonstrate the easy production of functionalized magnetic nanoparticles with suitably genetically modified magnetotactic bacteria that are efficient as a reusable nanobiocatalyst for pesticides bioremediation in contaminated effluents.

Desulfovibrio magneticus RS-1 contains an iron- and phosphorus-rich organelle distinct from its bullet-shaped magnetosomes.

Abstract: Intracellular magnetite crystal formation by magnetotactic bacteria has emerged as a powerful model for investigating the cellular and molecular mechanisms of biomineralization, a process common to all branches of life. Although magnetotactic bacteria are phylogenetically diverse and their crystals morphologically diverse, studies to date have focused on a few, closely related species with similar crystal habits. Here, we investigate the process of magnetite biomineralization in Desulfovibrio magneticus sp. RS-1, the only reported species of cultured magnetotactic bacteria that is outside of the alpha-Proteobacteria and that forms bullet-shaped crystals. Using a variety of high-resolution imaging and analytical tools, we show that RS-1 cells form amorphous, noncrystalline granules containing iron and phosphorus before forming magnetite crystals. Using NanoSIMS (dynamic secondary ion mass spectroscopy), we show that the iron-phosphorus granules and the magnetite crystals are likely formed through separate cellular processes. Analysis of the cellular ultrastructure of RS-1 using cryo-ultramicrotomy, cryo-electron tomography, and tomography of ultrathin sections reveals that the magnetite crystals are not surrounded by membranes but that the iron-phosphorus granules are surrounded by membranous compartments. The varied cellular paths for the formation of these two minerals lead us to suggest that the iron-phosphorus granules constitute a distinct bacterial organelle.

Large-scale production of magnetosomes by chemostat culture of Magnetospirillum gryphiswaldense at high cell density

Abstract: Magnetotactic bacteria have long intrigued researchers because they synthesize intracellular nano-scale (40-100 nm) magnetic particles composed of Fe3O4, termed magnetosomes. Current research focuses on the molecular mechanisms of bacterial magnetosome formation and its practical applications in biotechnology and medicine. Practical applications of magnetosomes are based on their ferrimagnetism, nanoscale size, narrow size distribution, dispersal ability, and membrane-bound structure. However, the applications of magnetosomes have not yet been developed commercially, mainly because magnetotactic bacteria are difficult to cultivate and consistent, high yields of magnetosomes have not yet been achieved. We report a chemostat culture technique based on pH-stat feeding that yields a high cell density of Magnetospirillum gryphiswaldense strain MSR-1 in an auto-fermentor. In a large-scale fermentor, the magnetosome yield was significantly increased by adjusting the stirring rate and airflow which regulates the level of dissolved oxygen (DO). Low concentration of sodium lactate (2.3 mmol l-1) in the culture medium resulted in more rapid cell growth and higher magnetosome yield than high concentration of lactate (20 mmol l-1). The optical density of M. gryphiswaldense cells reached 12 OD565 nm after 36 hr culture in a 42 L fermentor. Magnetosome yield and productivity were 83.23 ± 5.36 mg l-1 (dry weight) and 55.49 mg l-1 day-1, respectively, which were 1.99 and 3.32 times higher than the corresponding values in our previous study. Compared to previously reported methods, our culture technique with the MSR-1 strain significantly increased cell density, cell yield, and magnetosome yield in a shorter time window and thus reduced the cost of production. The cell density and magnetosome yield reported here are the highest so far achieved with a magnetotactic bacteria. Refinement of this technique will enable further increase of cell density and magnetosome yield.

South-Seeking Magnetic Bacteria

Abstract: Magnetotactic bacteria, originally discovered by Blakemore (1975), are by far the most convincing and abundant example of magnetically sensitive organisms in existence. Their magnetite crystals passively align the bacteria with the earth's magnetic field like a 3-dimensional compass (Frankel et al. 1979). These microaerophilic bacteria normally live in the soupy, oxygen-poor mud/water transition zone in many freshwater and marine environments. If the mud is disturbed so that the bacteria are exposed to oxygen-rich water, the species discovered so far (all from the northern hemisphere) swim rapidly along the direction of magnetic north. Because the magnetic field dips downward in the northern hemisphere, the bacteria eventually reach the mud/water interface again and avoid poisoning themselves with oxygen. Moench & Konetzka (1978) have devised an elegant technique to purify the bacterial population based on their swimming response - the bacteria will swim towards the south magnetic pole of a bar magnet placed near their jar, purifying themselves into a characteristic little pellet containing millions of individual cells. (The north geographic pole is magnetically south, so the bacteria were still trying to go to the north and down.) Two major questions concerning the behaviour of these bacteria need to be answered, however: (1) which way do they swim in the southern hemisphere, and (2) what do they do on the magnetic equator where the field is horizontal?

Ecophysiology of Magnetotactic Bacteria

Abstract: Magnetotactic bacteria are a physiologically diverse group of prokaryotes whose main common features are the biomineralization of magnetosomes and magnetotaxis, the passive alignment and active motility along geomagnetic field lines. Magnetotactic bacteria exist in their highest numbers at or near the oxic–anoxic interfaces (OAI) of chemically stratified aquatic habitats that contain inverse concentration gradients of oxidants and reductants. Few species are in axenic culture and many have yet to be well described. The physiology of those that have been described appears to dictate their local ecology. Known Fe 3 O 4-producing strains are microaerophiles that fix atmospheric nitrogen, a process mediated by the oxygen-sensitive enzyme nitrogenase. Marine Fe3O4-producing strains oxidize reduced sulfur species to support autotrophy through the Calvin–Benson–Bassham or the reverse tricarboxylic acid cycle. These organisms must compete for reduced sulfur species with oxygen, which chemically oxidizes these compounds, and yet the organism still requires some oxygen to respire with to catalyze these geochemical reactions. Most Fe3O4-producing strains utilize nitrogen oxides as alternate electron acceptors, the reductions of which are catalyzed by oxygen-sensitive enzymes. Fe3O4-producing magnetotactic bacteria must solve several problems. They must find a location where both oxidant (oxygen) and reductants (e.g., reduced sulfur species) are available to the cell and therefore in close proximity. They must also mediate oxygen-sensitive, ancillary biochemical reactions (e.g., nitrogen fixation) important for survival. Thus, the OAI appears to be a perfect habitat for magnetotactic bacteria to thrive since microaerobic conditions are maintained and oxidant and reductant often overlap.