Talk:Magnetosome

Possible updates

Hello, I would like to propose some edits. They would follow this outline.

New Plan:

Introduction: Magnetosome are membranous structures present in magnetotactic bacteria (MTB). They contain iron-rich magnetic particles that are enclosed within a lipid bilayer membrane. Each magnetosome can often contain 15 to 20 magnetite crystals that form a chain which acts like a compass needle to orient magnetotactic bacteria in geomagnetic fields, thereby simplifying their search for their preferred microaerophilicenvironments. Recent research has shown that magnetosomes are invaginations of the inner membrane and not freestanding vesicles.[2] Magnetite-bearing magnetosomes have also been found in eukaryotic magnetotactic algae, with each cell containing several thousand crystals. Overall, magnetosome crystals have high chemical purity, narrow size ranges, species-specific crystal morphologies and exhibit specific arrangements within the cell. These features indicate that the formation of magnetosomes is under precise biological control and is mediated biomineralization. Magnetotactic bacteria usually mineralize either iron oxide magnetosomes, which contain crystals of magnetite (Fe3O4), or iron sulfide magnetosomes, which contain crystals of greigite (Fe3S4). Several other iron sulfide minerals have also been identified in iron sulfide magnetosomes—including mackinawite (tetragonal FeS) and a cubic FeS—which are thought to be precursors of Fe3S4. One type of magnetotactic bacterium present at the oxic-anoxic transition zone (OATZ) of the southern basin of the Pettaquamscutt River Estuary, Narragansett, Rhode Island, United States is known to produce both iron oxide and iron sulfide magnetosomes.[3][4]

Formation of the Magnetosome: ● Biomineralization leads to the incredible degree of control the MBT impose on the formation of the mineral crystals within the magnetosomes. The process of biomineralization allows the MBT to control the shape and size along with the alignment of each individual magnetite crystal. ● The magnetite crystals are all identical within a species but between species they can vary in size, structure, formation, amount, but not purpose ● Organelle envelope creation? ○ Magnetosomes are prokaryotic membrane-bound organelles whose ○ Within the organelle there will either be ferrimagnetic crystals of magnetite (Fe3O4) or the iron sulfide greigite (Fe3S4). Recently there have been a few other magnetic compounds found but these are far less common ● About 20 magnetosome-specific proteins are used for the creation of a single magnetosome but telling the MTB what to do. ○ These proteins control vesicle formation, magnetosome iron transport, and the crystallization of the magnetites and their arrangement with in the particular vesicle. ○ acidic protein links the magnetosomes to a cytoskeletal structure within the cell -Genetics and cell biology of magnetosome formation in magnetotactic bacteria ● Contains iron oxide or sulfide ○ Analyses of a subunit of the MTB RNA sequences showed that all currently known magnetotactic bacteria that use iron oxide are associated with the specific subgroup of the Proteobacteria in the domain Bacteria. ○ Iron sulfide type are related to the sulfate-reducing bacteria within the other subdivision of the Proteobacteria. ○ This suggests independent evolution of the similar magnetotactic traits ○ Three general crystal morphologies have been reported in magnetotactic bacteria on the basis: roughly cuboidal, elongated prismatic (roughly rectangular), and tooth-, bullet- or arrowhead-shaped. Size of Magentotactic crystals ● Magnetatic crystals range in size from 30-120nm, this size allows them to be magnetically stable to help optimize the MTB abilty toward magnetotaxis. ○ Single-domain crystals have the maximum possible magnetic moment per unit volume for a given composition. ○ A smaller size would not be as efficient to contribute to the cellular magnetic moment, they are superparamagnetic so they are not continuously magnetic ○ Crystals exceeding 120nm can form magnetic domanis in oposition to the desired direction ● While a single magnetosome chain would appear to be ideal for magneto-aerotaxis, a number of magnetotactic bacteria have magnetosomes or magnetosome arrangements that depart from the ideal.[5] One reported example includes large (up to 200 nm) magnetosomes found in coccoid cells in Brazil. These cells have enough magnetosomes so that the calculated magnetic dipole moment of the cell is about 250 times larger than that of a typical cell of Magnetospirillum magnetotacticum. There are also examples of magnetotactic bacteria that contain hundreds of magnetosomes, many more than required for orientation. One large, rod-shaped organism, Magnetobacterium bavaricum, contains up to 1000 bulletshaped magnetosomes arranged in several chains traversing the cell. Some bacteria have magnetosomes that are not arranged in chains, but are clustered on one side of the cell. In such an arrangement, the shape anisotropy of each crystal provides the stability against remagnetization, rather than the overall shape anisotropy in the magnetosome chain arrangement. These non-ideal arrangements may be pointing to additional, currently unknown functions of magnetosomes, possibly related to metabolism. ○ ○ [Devel of dipoles paper]

Collapse of the Magnetosome: ● When the magnetotactic crystals are in an unstable arrangement the whole magnetosome will collapse without additional support ○ This collapse can occur during diagenesis and dolomitization ● magnetosome shape and elastic properties of biological membranes are the main thing holding the chains together along with the linearity and the connection to the cytoskeleton. ● The extent of the geometries effect for stablizing the magnetosome chains shows that they are intrinsically unstable ● “Although it has been speculated that the cell wall and associated membrane structures act to prevent magnetosome chain collapse, our data indicate that magnetosome linearity persists long after cells are disrupted. This is consistent with prior observations that in some magnetotcocci the magnetosome chains pass through the cell interior, precluding continuous contact with the cell wall and implying additional support structures exist in some species.” - Experimental observation of magnetosome chain collapse in magnetotactic bacteria: Sedimentological, paleomagnetic, and evolutionary implications

One 

Purpose of the Magnetosome: ● “Magnetotactic bacteria (MTB) are widespread, motile, diverse prokaryotes that biomineralize a unique organelle called the magnetosome. Magnetosomes consist of a nano-sized crystal of a magnetic iron mineral that is enveloped by a lipid bilayer membrane. In cells of almost all MTB, magnetosomes are organized as a well-ordered chain. The magnetosome chain causes the cell to behave like a motile, miniature compass needle where the cell aligns and swims parallel to magnetic field lines. “ -Ecology, Diversity, and Evolution of Magnetotactic Bacteria ● The magnetic dipole moment of the cell is usually large enough such that its interaction with Earth's magnetic field overcomes thermal forces that tend to randomize the orientation of the cell in its aqueous surroundings. Magnetotactic bacteria also use aerotaxis, a response to changes in oxygen concentration that favors swimming toward a zone of optimal oxygen concentration. In lakes or oceans the oxygen concentration is commonly dependent on depth. As long as the Earth's magnetic field has a significant downward slant, the orientation along field lines aids the search for the optimal concentration. This process is called magneto-aerotaxis.

Thank you, Helainaann (talk) 22:20, 13 April 2018 (UTC)

internal inconsistency

First, this page says:

One type of magnetotactic bacterium present at the oxic-anoxic transition zone (OATZ) of the southern basin of the Pettaquamscutt River Estuary, Narragansett, Rhode Island, United States is known to produce both iron oxide and iron sulfide magnetosomes.

But then later, it says:

The MTB may either have iron oxide or sulfide but not both.

This seems inconsistent to me. 136.153.22.70 (talk) 08:25, 22 March 2023 (UTC)