Topic
Magnetotactic bacteria
About: Magnetotactic bacteria is a research topic. Over the lifetime, 1118 publications have been published within this topic receiving 43741 citations.
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TL;DR: In this article, the authors studied the time course of magnetosome growth and chain formation in magnetospirillum magneticum AMB-1 by transmission electron microscopy (TEM) observation and rock magnetism.
Abstract: SUMMARY Stable single-domain (SD) magnetite formed intracellularly by magnetotactic bacteria is of fundamental interest in sedimentary and environmental magnetism In this study, we studied the time course of magnetosome growth and magnetosome chain formation (0–96 hr) in Magnetospirillum magneticum AMB-1 by transmission electron microscopy (TEM) observation and rock magnetism The initial non-magnetic cells were microaerobically batch cultured at 26 ◦ C in a modified magnetic spirillum growth medium TEM observations indicated that between 20 and 24 hr magnetosome crystals began to mineralize simultaneously at multiple sites within the cell body, followed by a phase of rapid growth lasting up to 48 hr cultivation The synthesized magnetosomes were found to be assembled into 3–5 subchains, which were linearly aligned along the long axis of the cell, supporting the idea that magnetosome vesicles were linearly anchored to the inner membrane of cell By 96 hr cultivation, 14 cubo-octahedral magnetosome crystals in average with a mean grain size of ∼445 nm were formed in a cell Low-temperature (10–300 K) thermal demagnetization, room-temperature hysteresis loops and first-order reversal curves (FORCs) were conducted on whole cell samples Both coercivity (47–181 mT) and Verwey transition temperature (100–106 K) increase with increasing cultivation time length, which can be explained by increasing grain size and decreasing nonstoichiometry of magnetite, respectively Shapes of hysteresis loops and FORCs indicated each subchain behaving as an ‘ideal’ uniaxial SD particle and extremely weak magnetostatic interaction fields between subchains Low-temperature thermal demagnetization of remanence demonstrated that the Moskowitz test is valid for such linear subchain configurations (eg δ FC/δ ZFC > 20), implying that the test is applicable to ancient sediments where magnetosome chains might have been broken up into short chains due to disintegration of the organic scaffold structures after cell death These findings provide new insights into magnetosome biomineralization of magnetotactic bacteria and contribute to better understanding the magnetism of magnetofossils in natural environments
80 citations
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TL;DR: The magnetic properties of intact magnetosome chains in magnetospirillum gryphiswaldense bacteria were investigated by means of static and dynamic magnetic analyses and ferromagnetic resonance spectroscopy as mentioned in this paper.
80 citations
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TL;DR: A model in which MamX, MamZ and MamH functionally interact to balance the redox state of iron within the magnetosome compartment is proposed.
Abstract: Magnetospirillum gryphiswaldense uses intracellular chains of membrane-enveloped magnetite crystals, the magnetosomes, to navigate within magnetic fields. The biomineralization of magnetite nanocrystals requires several magnetosome-associated proteins, whose precise functions so far have remained mostly unknown. Here, we analysed the functions of MamX and the Major Facilitator Superfamily (MFS) proteins MamZ and MamH. Deletion of either the entire mamX gene or elimination of its putative haem c-binding magnetochrome domains, and deletion of either mamZ or its C-terminal ferric reductase-like component resulted in an identical phenotype. All mutants displayed WT-like magnetite crystals, flanked within the magnetosome chains by poorly crystalline flake-like particles partly consisting of haematite. Double deletions of both mamZ and its homologue mamH further impaired magnetite crystallization in an additive manner, indicating that the two MFS proteins have partially redundant functions. Deprivation of ΔmamX and ΔmamZ cells from nitrate, or additional loss of the respiratory nitrate reductase Nap from ΔmamX severely exacerbated the magnetosome defects and entirely inhibited the formation of regular crystals, suggesting that MamXZ and Nap have similar, but independent roles in redox control of biomineralization. We propose a model in which MamX, MamZ and MamH functionally interact to balance the redox state of iron within the magnetosome compartment.
79 citations
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TL;DR: The results show that some magnetotactic bacteria can be considered extremophilic and greatly extend the known ecology of magnettactic bacteria and the conditions under which they can biomineralize magnetite.
Abstract: SummaryLarge numbers of magnetotactic bacteria were dis-covered in mud and water samples collected from anumber of highly alkaline aquatic environments withpH values of ~ 9.5. These bacteria were helical in mor-phology and biomineralized chains of bullet-shapedcrystals of magnetite and were present in all thehighly alkaline sites sampled. Three strains from dif-ferent sites were isolated and cultured and grew opti-mally at pH 9.0–9.5 but not at 8.0 and below,demonstrating that these organisms truly requirehighly alkaline conditions and are not simplysurviving/growing in neutral pH micro-niches intheir natural habitats. All strains grew anaerobicallythrough the reduction of sulfate as a terminal electronacceptor and phylogenetic analysis, based on 16SrRNA gene sequences, as well as some physiologicalfeatures, showed that they could represent strains of Desulfonatronum thiodismutans , a known alkaliphilicbacterium that does not biomineralize magneto-somes. Our results show that some magnetotacticbacteria can be considered extremophilic and greatlyextend the known ecology of magnetotactic bacteriaand the conditions under which they can biomineral-ize magnetite. Moreover, our results show that thistype of magnetotactic bacterium is common in highlyalkaline environments. Our findings also greatlyinfluence the interpretation of the presence ofnanometer-sized magnetite crystals, so-called mag-netofossils, in highly alkaline environments.Introduction
79 citations
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TL;DR: In this article, the magnetism, geochemistry and geobiology of uncultured magnetite and greigite-producing magnetotactic bacteria (MB) and magnetically responsive protists (MRP) in Salt Pond (Falmouth, MA, USA), a small coastal, marine basin (∼5 m deep) that becomes chemically stratified during the summer months.
Abstract: SUMMARY Magnetic properties of suspended material in the water columns of freshwater and marine environments provide snapshots of magnetic biomineralization that have yet to be affected by the eventual time-integration and early diagenetic effects that occur after sediment deposition. Here, we report on the magnetism, geochemistry and geobiology of uncultured magnetite- and greigite-producing magnetotactic bacteria (MB) and magnetically responsive protists (MRP) in Salt Pond (Falmouth, MA, USA), a small coastal, marine basin (∼5 m deep) that becomes chemically stratified during the summer months. At this time, strong inverse O2 and H2S concentration gradients form in the water column and a well-defined oxic–anoxic interface (OAI) is established at a water depth of about 3.5 m. At least four morphological types of MB, both magnetite and greigite producers, and several species of magnetically responsive protists are found associated with the OAI and the lower sulphidic hypolimnion. Magnetic properties of filtered water were determined through the water column across the OAI and were consistent with the occurrence of magnetite- and greigite-producing MB at different depths. Sharp peaks in anhysteretic remanent magnetization (ARM) and saturation isothermal remanent magnetization (SIRM) and single-domain (SD) values of ARM/SIRM occur within the OAI corresponding to high concentrations of MB and MRP with magnetically derived cell densities of 10 4 –10 6 ml −1 . Low-temperature ( 1 per cent) is present within magnetite magnetosomes, produced either
79 citations