Nav: Home

New tool for studying magnetic, self-propelled bacteria that resemble compass needles

September 15, 2015

WASHINGTON, D.C., September 15, 2015 -- In the Marvel Comics universe, Professor Xavier and the X-Men are only able to fend off their archrival Magneto, the magnetic mutant with the ability to control metals, once they truly understand the scope of the villain's powers. To better understand the behavior of the microbial world's Magnetos -- the magnetically influenced water-dwellers known as magnetotactic bacteria -- three researchers from Europe and Russia have developed a new tool that allows these unique microscopic species to be studied more easily, especially in their natural environment.

The researchers describe their work in the journal Review of Scientific Instruments, from AIP Publishing.

Magnetotactic bacteria can be found in both freshwater and marine environments. What makes them magnetic is that they produce chains of organelles (compartments located inside the bacterial cell wall) called magnetosomes that contain nanometer-size iron crystals. The earth's magnetic field puts a torque on the magnetosome chains, rotating the bacteria in which they reside. This causes the bacteria to swim in the direction of the applied external force.

"In other words, magnetotactic bacteria act as self-propelled compass needles," said Pieter Smid, a geophysicist with Ludwig-Maximilians-Universität in Munich, Germany and the University of Nottingham in the United Kingdom. "Their magnetic abilities help them find a chemically suitable habitat in which to thrive."

Smid said that magnetotactic bacteria are important creatures to study because they can provide scientific insight into how our planet's sedimentary layers were formed. "When these microbes die in aqueous sediments, their magnetosomes are conserved in the rocks formed from that sediment," he explained. "The magnetic properties are permanently imparted to the rock which, in turn, serves as a record of changes in the earth's magnetic fields and provides us with a timeline for the rock's creation."

Additionally, Smid said that magnetotactic bacteria may one day be used as indicators of impending environmental and climate change, or as microscopic transport systems for nanoparticles.

Making Study of Magnetotactic Bacteria More "Attractive"

Despite the interest from scientists, studying magnetotactic bacteria hasn't proved easy, especially in the field.

"In the past, two pairs of electromagnetic coils were wrapped around a microscope to control the swimming direction of the magnetotactic bacteria," Smid said. "These multicomponent systems required large power supplies, complex electromagnetic frameworks, much electronic circuitry and control software -- not the kind of mechanism that's suitable for outside-the-lab experiments."

Conventional magnets also produced magnetic fields that were difficult to control, with waves of varying intensities filling the microscope viewing area. Such variations, Smid said, often played havoc with measurements being performed on samples of magnetotactic bacteria.

Smid and colleagues solved these problems by designing a simple mechanism using a single rotating permanent magnet. Their device resembles the inner workings of a watch, with the magnet positioned atop a concentric series of five gears turning in sync to create a strictly controlled and easily manipulated rotating magnetic field.

"The permanent magnet in our mechanism moves along a circular trajectory while rotating around its dipole axis [the center point between the north and south poles of the magnet]," Smid said. "As the magnet turns, it generates a magnetic field of constant amplitude [intensity] and when we place this next to a microscope, it drives the magnetotactic bacteria on the scope to swim in a circular motion and keeps them in view."

By measuring the radius of each circle the magnetotactic bacteria travel as the magnet rotates faster and faster, the researchers can accurately determine swimming speed. This is a key to better understanding how the bacteria move in a magnetic field and how those dynamics might be used in future applications.

When the frequency of the magnetic field rotation increases to the point that the bacteria will no longer follow the generated field, they break out of their circular swimming pattern. "This specific frequency, known as the 'escape frequency,' can be used to calculate a bacterium's magnetic moment -- the measure of its ability to align with a magnetic field," Smid explained.

Simple System, Many Advantages

The success of the simple concentric rotating magnet device reported in the Review of Scientific Instruments paper was unexpected, Smid said. "We didn't believe that we could produce a rotating magnetic field of constant amplitude, but the results showed that our system does what conventional electromagnets can do with less equipment, lower cost and most importantly, more flexibility, since it can be adapted to many light microscopes and taken into the field," he said.

Next up for the researchers will be testing their new tool on different species of magnetotactic bacteria in different environments. They hope to begin answering questions such as how populations respond and adapt to a wide range of magnetic fields, and how the magnetic properties of these special microbes can best be put to use.
The article, "Microscopic observation of magnetic bacteria in the magnetic field of a permanent rotating magnet," is authored by Pieter Smid, Valeriy Shcherbakov and Nikolai Petersen. It will be published in the journal Review of Scientific Instruments on September 15, 2015 (DOI: 10.1063/1.4929331). After that date, it can be accessed at:

The authors of this paper are affiliated with the Ludwig-Maximilians-Universität; the University of Nottingham; the Geophysical Observatory Borok IFZ RAS, Russia; and the Federal University, Russia.


Review of Scientific Instruments publishes original research and review articles on instruments in physics, chemistry, and the life sciences. The journal also includes sections on new instruments and new materials. See:

American Institute of Physics

Related Bacteria Articles:

Bacteria might help other bacteria to tolerate antibiotics better
A new paper by the Dynamical Systems Biology lab at UPF shows that the response by bacteria to antibiotics may depend on other species of bacteria they live with, in such a way that some bacteria may make others more tolerant to antibiotics.
Two-faced bacteria
The gut microbiome, which is a collection of numerous beneficial bacteria species, is key to our overall well-being and good health.
Microcensus in bacteria
Bacillus subtilis can determine proportions of different groups within a mixed population.
Right beneath the skin we all have the same bacteria
In the dermis skin layer, the same bacteria are found across age and gender.
Bacteria must be 'stressed out' to divide
Bacterial cell division is controlled by both enzymatic activity and mechanical forces, which work together to control its timing and location, a new study from EPFL finds.
How bees live with bacteria
More than 90 percent of all bee species are not organized in colonies, but fight their way through life alone.
The bacteria building your baby
Australian researchers have laid to rest a longstanding controversy: is the womb sterile?
Hopping bacteria
Scientists have long known that key models of bacterial movement in real-world conditions are flawed.
Bacteria uses viral weapon against other bacteria
Bacterial cells use both a virus -- traditionally thought to be an enemy -- and a prehistoric viral protein to kill other bacteria that competes with it for food according to an international team of researchers who believe this has potential implications for future infectious disease treatment.
Drug diversity in bacteria
Bacteria produce a cocktail of various bioactive natural products in order to survive in hostile environments with competing (micro)organisms.
More Bacteria News and Bacteria Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at