Bacteria uses Earth’s Geomagnetic Field to Navigate by synthesizing Nano-sized compasses 

Hey Steemians, 

Today in the series of Microbial world, I’ll be discussing on the movement of microbes (bacteria). You must have learned about the movement of bacteria, how they move? Can they control their movement or basically what pattern they follow to move and how they navigate themselves?

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For those who don’t know about the shape of bacteria and what parts do they have? Bacteria can be of either rod shaped or cocci (round) shaped, basically they are divided into five different shapes but mostly they categorized in these two forms. So, if you look the bacterial cell, you will find these parts a cell, a flagella attached to it (if the bacteria is motile) and pilus (for attachment). These flagella are responsible for the movement, they rotate same like a motor clockwise (backward) and anticlockwise (forward), representing their movement.  

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You can easily see their movement in microscope, there are some species which instead of moving forward or reverse they tumble and covers the distance. So, the point today’s discussion is how do they do it?

Magnetic Iron nanominerals are synthesized by Magnetotactic Bacteria, they function as tiny compasses which provide navigation using Earth’s geomagnetic field. 

Being most abundant element on earth, Iron is also an essential nutrient for all organism. It has a reduced state ferrous ion Fe(II) and an oxidized state ferric ion Fe(III), Iron present in ferric state in the aerobic environment and in anaerobic environment iron is present in the ferrous state. Iron cycle is bit complex earth’s biogeochemically and includes both biotic and abiotic types of oxidizing and reducing components.

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A group of microorganism, called magnetotactic bacteria play’s a major role in the Earth’s iron cycle. Iron is very important for group of these magnetotactic bacteria not only because iron functions in many of their metabolic pathways but also because these group of bacteria store nanometer sized iron minerals incorporated in their body (1). 

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Magnetotactic bacteria were first documented in 1975 by Blakemore and was found that these bacteria are synthesizing a chain of nano sized magnetic particles, which is functioning as compass needle for the direction. These nano needles allowing the microbes to orient themselves in earth’s geomagnetic field. Bacteria synthesizes small magnetic particles by set of specified proteins and are present in membrane bound organelles called Magnetosomes (2). These nanoparticles in the bacteria provides the magnetic dipole to cell and allow them to sense Earth’s geomagnetic field. These magnetotactic bacteria also have flagella which provide them the mobility (3).

The process where bacteria moves according to the geomagnetic field and use their flagella to swim to anaerobic and redox environment is known as magnetotaxis. These bacteria are divided into three groups mainly on the basis of their synthesized magnetic minerals: magnetite, greigite or a combination of greigite and pyrite and a combination of magnetite and greigite (4). Few magnetite producing bacteria are cultivated in pure culture while still no bacteria producing gregite are cultured in pure form. These group of bacteria mostly present in the marine environment with less oxygen and high concentration of hydrogen sulfide. In addition to the contribution of iron cycle these hydrogen sulfide producing bacteria also plays a major role in the biogeochemical cycle of sulfur (5).

The process by which these magnetotactic bacteria synthesizes the Fe3O4 is still not clear. It is believed that several distinct steps are involved in this biomineralization process, which includes iron uptake by bacterial cell, formation of magnetosomes vesicle within bacteria, iron transport into these vesicles and protein mediated biomineralization within magnetosomes. Iron uptake in these bacteria vary from species to species, all this depends on the pH in which they survive making it oxidized or reduced (6).

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Iron exist as Fe(III) in earth crust and insoluble at neutral pH, In order to utilize solid Fe(III) some bacterial sp. are known to synthesize iron-binding molecules called siderophore (7). These biomolecules are ferric ion chelators, after forming complex with the Fe(III) it enters the bacterial cell and then the Fe(III) get cleaved. Once inside, Fe(III) gets converted to Fe(II) which is taken up by the magnetosomes. MamB and MamM are observed to be responsible for the transport of iron into the magnetosomes (8).

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Researchers have suggested that organism similar to Earth’s magnetotactic bacteria may be present in other planet too.

References

Dennis et. al., 1995 Controlled Biomineralization of Magnetite (Fe3O4) and Greigite (Fe3S4) in a Magnetotactic Bacterium. 3232-3239

Gorby et. al., 1988 Characterization of the bacterial magnetosome membrane. 170(2); 834-841

Haltia et. al., 2009 Magnetic properties and environmental changes recorded in Lake Lehmilampi (Finland) during the Holocene. 43(1);1-13

Damien at. al., 2008 Magnetotactic Bacteria and Magnetosomes. 108(11);4875-4898

Komeili et. al., 2004 Magnetosome vesicles are present before magnetite formation, and MamA is required for their activation. 101(11);3839-3844

Atsushi et.al., 2003 A Novel Protein Tightly Bound to Bacterial Magnetic Particles in Magnetospirillum magneticum Strain AMB-1. 

Neilands et.al., 1995 Siderophores: Structure and Function of Microbial Iron Transport Compounds. 

Previous articles on Microbial World

Microbial World #4 Neurotoxins in your gut 

Microbial World #5 Rise of Superbugs

Microbial World #6 Bioluminescent Bacteria

Microbial World #7 Halocin: Bacteriocin from halobacteria 

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Happy Reading :)

Vinamra