Magnetotactic Bacteria

Introduction to Magnetotactic Bacteria

Figure 1 - Model of magneto-aeotaxis. Magnetotactic bacteria (black) use the earth's magnetic field (gray lines) as guides to localize to the OATZ while other organisms (white) must rely on other methods for finding the same region. Courtesy of Komeili (http://femsre.oxfordjournals.org/content/36/1/232.figures-only)

        Magnetotactic bacteria (MB) are gram-negative bacteria that build specialized organelles called magnetosomes in order to store magnetic material and align themselves with the earth’s magnetic field. Magnetotactic bacteria were first described in 1975 when Richard Blakemore realized that a specific group of bacteria he collected from sediment constantly swam in the same geographic direction, regardless of the positioning of the microscope or external stimuli ^[1]. MB are mostly found in shallow aquatic environments where oxygen and other redox compounds are horizontally stratified and many described magnetotactic bacteria localize at or close to the oxic anoxic transition zone (OATZ)—a region in the water column that has very low oxygen levels ^[2]. The current model (shown in Figure 1) to explain the selective advantage provided by magnetosomes is that magnetotactic bacteria are able to locate the OATZ much easier than bacteria that solely use chemotactic and aerotactic mechanisms ^[3].
         Although the magneto-aerotaxis model has been widely accepted amongst the scientific community, new research is suggesting that the behavior magnetotactic bacteria exhibit in the environment may be more complicated than a simple response to oxygen levels:

• Some MB species also show [ phototactic] response, which helps reinforce magneto-aerotactic behavior and repel them from surface waters ^{[4, 5]}
• Genome sequences show that MB have some of the highest numbers of signaling proteins of Bacteria ^[6]

Magnetospirillum gryphiswaldense (also referred to as MSR-1) is a gram negative magnetotactic bacteria that is found in shallow fresh water and sediment. They are characterized by a spirillial morphology with flagella at each end of the cell. They are able to orient themselves based on Earth’s magnetic field (magnetotaxis) due to special organelles called magnetosomes.

Other examples:
Bold
Italic
Subscript: H₂O
Superscript: Fe ^[2]

Magnetosome Formation

Electron micrograph of Magnetospirillum gryphiswaldense cells containing chains of magnetite crystals (top) and magnified section of crystal chain (bottom). By Caulobacter subvibrioides (Diskussion) GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

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Genetic Influences

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Potential Uses in Bioremediation

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References

[1] Blakemore, R. (1975). Magnetotactic bacteria. Science (New York, N.Y.), 190(4212), 377-379.

[2] Simmons, S. L., Sievert, S. M., Frankel, R. B., Bazylinski, D. A., & Edwards, K. J. (2004). Spatiotemporal distribution of marine magnetotactic bacteria in a seasonally stratified coastal salt pond. Applied and Environmental Microbiology, 70(10), 6230-6239.

[3] Komeili, A. (2012). Molecular mechanisms of compartmentalization and biomineralization in magnetotactic bacteria. FEMS Microbiology Reviews, 36(1), 232-255.

[4] Chen, C., Ma, Q., Jiang, W., & Song, T. (2011). Phototaxis in the magnetotactic bacterium magnetospirillum magneticum strain AMB-1 is independent of magnetic fields. Applied Microbiology and Biotechnology, 90(1), 269-275.

[5] Shapiro, O. H., Hatzenpichler, R., Buckley, D. H., Zinder, S. H., & Orphan, V. J. (2011). Multicellular photo‐magnetotactic bacteria. Environmental Microbiology Reports, 3(2), 233-238.

[6] Alexandre, G., Greer-Phillips, S., & Zhulin, I. B. (2004). Ecological role of energy taxis in microorganisms. FEMS Microbiology Reviews, 28(1), 113-126.

Other References:

[] Bazylinski, D. A., & Schübbe, S. (2007). Controlled biomineralization by and applications of magnetotactic bacteria. Advances in applied microbiology, 62, 21-62.