Magnetotactic bacteria and their application

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Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.

Figure 1. The gram negative, anaerobic Fusobacterium necrophorum exhibiting bacilli morphology in a photomicrograph after being cultured for 48 hours in thioglycollate medium. Credit to CDC/ Dr. V. R. Dowell, Jr. in 1972. Image obtained from CDC Public Health Image Library.

By Grant Miner

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Legend/credit: Electron micrograph of the Ebola Zaire virus. This was the first photo ever taken of the virus, on 10/13/1976. By Dr. F.A. Murphy, now at U.C. Davis, then at the CDC.
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Figure 2. Possible outcomes of infection with Fusobacterium necrophorum. The bacteria can cause a wide range of problems within the host, and this flowchart demonstrates the necessary intermediate steps to pass from one condition to another. Credit to Terry Riordan, 2007. Image obtained from Clin Microbiol Rev.

Overview

Magnetotactic bacteria (MTB) are a polyphyletic group of Gram-negative prokaryotes. Members of this group are characterized by their ability to align themselves and swim along a magnetic field. They owe this ability to the magnetosome, a specific intracellular structure that contains crystals of of magnetic metals (usually magnetite or greigite) bounded by a membrane. They were discovered in 1975 by Richard Blakemore. In his paper “Magnetotactic Bacteria” (Blakemore coined the name), which he observed bacteria migrating along geomagnetic lines and, upon investigation, the magnetosome. This discovery impacted the scientific communities across many disciplines, including geology, mineralogy, chemistry, biochemistry, physics, oceanography, and, of course, microbiology. Because all species of MTB require microaerobic conditions, few species have been cultivated in pure condition. Because of this, they are relatively difficult to use in biotechnology. Nevertheless, researchers have succeeded in making headway in utilizing these strange organisms.

Physiology and Ecology

MTB usually inhabit sediments and water columns with vertical chemical stratification. Like many, bacteria, MTB’s main mode of taxis is through their helical flagella. Magnetotaxis causes these bacteria to orient themselves northward along geographic lines while in the northern hemisphere, and southward while in the southern. Interestingly enough, MTB are observed to swim both directions while along the equator. As a general rule, MTB are anaerobes, microaerophiles or facultatively anaerobic microaerophiles. Because of this, they are most likely to found at the the borders of oxic-anoxic regions as well as the anoxic regions of their habitat. In terms of a more physical placement within their habitat, MTB are most likely to be found at the water-sediment interface or thereabouts. A number of morphological types can be found within the MTB group including cocci, spirilla, vibrios and multicellular forms. MTB biomineralized two groups of metals: iron oxides and iron sulfides. Those species that produce iron sulfides biomineralized greigite (Fe3S4), while those that produce iron oxides biomineralized magnetite (Fe3O4). Additionally, species have been found that produce both and have magnetosomes that contain both magnetite and greigite. Geographic distribution of MTB’s are as widely varied as their morphology. As of today, only oxide-producers have been found in freshwater environments, which range from North America to Asia. MTB are even found within more extreme environments, such as lake Mono in California, an alkaline and saline in which the low solubility of iron makes the survival of MTB very difficult. Additionally, MTB are commonly found within the anoxic layers of marine environments, usually near the sedimentary layer.

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References

Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2016, Kenyon College.