Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK

Komeili, Arash; Li, Zhuo; Newman, Dianne K.; Jensen, Grant J.

doi:10.1126/science.1123231

Cited by 580 publications

(759 citation statements)

References 22 publications

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“…2a. The magnetosome chains are situated inside the cytoplasmic membrane of the bacterium, held together by networks of actin-like filaments 26 (Fig. 2a, white arrow).…”

Section: Resultsmentioning

confidence: 99%

“…Materials characterization techniques are typically aimed at direct observations of the magnetite nucleation and growth at high spatial resolution. High resolution TEM is often used to observe formation of magnetosomes in magnetotactic bacteria via cryogenic TEM (cryo-TEM) 4,[22][23][24][25][26][27][28][29] . This technique provides vital information about organization of the cellular structures and development of the magnetosomes 20,27 .…”

mentioning

confidence: 99%

“…However, the vitreous ice environment of cryo-TEM samples may not be entirely representative of the native hydrated cellular state, and may introduce artifacts due to the preparatory protocols often involving addition of cryo-protectants, thin sectioning, and sample staining. Fluorescence microscopy is often employed in conjunction with TEM imaging to study dynamic biomolecular processes in magnetotactic bacteria, such as localization of membrane proteins during bacteria growth 20,26 . The spatial resolution of fluorescence microscopy is limited by the diffraction limit to ,200 nm, so establishing connections between biomolecular processes and magnetosome growth mechanisms relies on correlation with cryo-TEM.…”

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confidence: 99%

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Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

et al. 2015

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Magnetotactic bacteria biomineralize ordered chains of uniform, membrane-bound magnetite or greigite nanocrystals that exhibit nearly perfect crystal structures and species-specific morphologies. Transmission electron microscopy (TEM) is a critical technique for providing information regarding the organization of cellular and magnetite structures in these microorganisms. However, conventional TEM can only be used to image air-dried or vitrified bacteria removed from their natural environment. Here we present a correlative scanning TEM (STEM) and fluorescence microscopy technique for imaging viable cells of Magnetospirillum magneticum strain AMB-1 in liquid using an in situ fluid cell TEM holder. Fluorescently labeled cells were immobilized on microchip window surfaces and visualized in a fluid cell with STEM, followed by correlative fluorescence imaging to verify their membrane integrity. Notably, the post-STEM fluorescence imaging indicated that the bacterial cell wall membrane did not sustain radiation damage during STEM imaging at low electron dose conditions. We investigated the effects of radiation damage and sample preparation on the bacteria viability and found that approximately 50% of the bacterial membranes remained intact after an hour in the fluid cell, decreasing to ,30% after two hours. These results represent a first step toward in vivo studies of magnetite biomineralization in magnetotactic bacteria.B iomineralization is a widespread biological phenomenon occurring in living organisms ranging from single cells to complex multicellular organisms. Biomineralization of inorganic materials in single cell organisms is an ideal system for studying fundamental mechanisms of biomineralization 1 . Model systems range from prokaryotic organisms, such as magnetite formation in magnetotactic bacteria 2-4 , to eukaryotic organisms, such as silica biomineralization in diatoms 5,6 . Understanding biomineralization in these organisms in terms of crystal nucleation and growth, as well as the involvement of biological macromolecules and cellular processes, is of fundamental interest to scientists as similar principles can be used to develop synthetic nanomaterials.Magnetite biomineralization by magnetotactic bacteria is a topic of great interest in nanotechnology 7-12 , functional materials [11][12][13][14][15][16] , and astrobiology 17 . Magnetotactic bacteria take up soluble iron species that they use to biomineralize chains of magnetite nanocrystals, known as magnetosomes, in intracellular membrane vesicles 2 . The nanocrystals have nearly perfect mineral crystal structures with consistent species-specific morphologies, leading to well-defined magnetic properties 2,3,9,12,18,19 . As a result, magnetotactic bacteria are one of the best model systems for investigating the molecular mechanisms of biomineralization. Magnetite biomineralization in these bacteria is a complex process involving a number of steps including cellular uptake and reduction of ferric ions, complexation of the iron with membrane proteins, an...

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“…2a. The magnetosome chains are situated inside the cytoplasmic membrane of the bacterium, held together by networks of actin-like filaments 26 (Fig. 2a, white arrow).…”

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

et al. 2015

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“…Crucial proteins for BacMP alignment in the cell were also reported. MamK is a homologue of the bacterial actin-like protein, and is revealed to form filaments to establish the chain-like structure of BacMPs through appropriate subcellular targeting (Komeili et al 2006). MamK nucleates at multiple sites to form long filaments that were confirmed via protein expression in Escherichia coli (Pradel et al 2006).…”

Section: Protein Analyses Of the Bacmp Membranementioning

confidence: 99%

Formation of magnetite by bacteria and its application

Arakaki

Nakazawa

Nemoto

et al. 2008

J. R. Soc. Interface.

220

176

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Magnetic particles offer high technological potential since they can be conveniently collected with an external magnetic field. Magnetotactic bacteria synthesize bacterial magnetic particles (BacMPs) with well-controlled size and morphology. BacMPs are individually covered with thin organic membrane, which confers high and even dispersion in aqueous solutions compared with artificial magnetites, making them ideal biotechnological materials. Recent molecular studies including genome sequence, mutagenesis, gene expression and proteome analyses indicated a number of genes and proteins which play important roles for BacMP biomineralization. Some of the genes and proteins identified from these studies have allowed us to express functional proteins efficiently onto BacMPs, through genetic engineering, permitting the preservation of the protein activity, leading to a simple preparation of functional protein-magnetic particle complexes. They were applicable to high-sensitivity immunoassay, drug screening and cell separation. Furthermore, fully automated single nucleotide polymorphism discrimination and DNA recovery systems have been developed to use these functionalized BacMPs. The nano-sized fine magnetic particles offer vast potential in new nano-techniques.

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“…These bacteria contain a linear array of magnetosomes along a straight line within the helical cell body, through which they can orient themselves within a magnetic field [Scheffel et al, 2006]. The actin/MreB-like MamK protein forms a straight filament in Magnetospirillum cells [Komeili et al, 2006] and also when expressed in E. coli cells [Pradel et al, 2006]. Apparently together with MamJ, it is essential for the alignment of magnetosomes, which appear to be generated through membrane invaginations.…”

Section: Mreb Parm and Other Bacterial Actin-like Proteinsmentioning

confidence: 99%

Dynamics of bacterial cytoskeletal elements

Graumann

2009

Cell Motil. Cytoskeleton

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Bacterial cytoskeletal elements are involved in an astonishing spectrum of cellular functions, from cell shape determination to cell division, plasmid segregation, the positioning of membrane-associated proteins and membrane structures, and other aspects of bacterial physiology. Interestingly, these functions are not necessarily conserved, neither between different bacterial species nor between bacteria and eukaryotic cells. The flexibility of cytoskeletal elements in performing different tasks is amazing and emphasises their very early development during evolution. This review focuses on the dynamics of cytoskeletal elements from bacteria. Cell Motil. Cytoskeleton 66: 909-914, 2009. '

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Magnetosomes Are Cell Membrane Invaginations Organized by the Actin-Like Protein MamK

Cited by 580 publications

References 22 publications

Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging

Formation of magnetite by bacteria and its application

Dynamics of bacterial cytoskeletal elements

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