We have known for a long time that the bacterium Magnetococcus marinus, present in marine sediments, could advance by swimming at the bottom of theocean. What was less known, however, was the speed at which she could travel.
In partnership with scientists Germans from the Max Planck Institute in Potsdam and the University of Göttingen, a team of French researchers from the Aix-Marseille Institute of Biosciences and Biotechnology therefore examined the trajectory of this microorganism by a method combining observation of bacteria under the microscope and digital sound simulation movement. The results of these analyzes, presented in a study published by the journal eLife January 28, 2020, indicate that Magnetococcus marinus describes complex spirals at a speed never before observed in a bacteria: it is able, in one second, to travel a distance equivalent to almost 500 times its own size.
If such work makes it possible to specify the morphology of Magnetococcus marinus and to better understand the mobility of so-called “micro-swimmers” microorganisms, they could also find environmental applications or in medical micro-robotics.
A fast bacteria with two flagella
” Bacteria propel and change direction by spinning long helical filaments, called flagella“, Recall the authors of the study in a communicated dated February 25, 2020. These flagella, according to their number, their arrangement around the micro-organism and their direction of rotation, determine, like the engines of a boat, the characteristics of the movement of each species of bacteria. . Other cells than bacteria may have flagella. This is for example the case of human sperm, the flagellum of which goes up the female genital tract to the ovum.
We have known for a long time that Magnetococcus marinus, a round bacteria with a diameter of about 1 micrometer, was able to move forward. We had noticed that the trajectory of this bacterium became more complex in the presence of a magnetic field – it is this sensitivity to the magnetic field, linked to the presence of organelles called magnetosomes in the cell, which had given its genus name to the bacterium Magnetococcus marinus. We even called this complex trajectory helical. Therefore, it was thought that Magnetococcus marinus had two groups of flagella all attached to the same hemisphere of the cell, as if the microorganism had two bundles of tails: it was assumed that the bacteria was swimming cell body forward, flagella towards the back to propel the microorganism. In addition, it has been estimated until today that the swimming speed of Magnetococcus marinus at 100 micrometers per second (µm / s).
The work of researchers at the University of Aix-Marseille, however, showed that we were wrong. Subjected to a magnetic field, the bacterium adopts a much more complex trajectory than that which we had identified: it describes double, even triple spirals. ” Magnetococcus marinus made [donc] sort of complex loops“, Say the authors in a press release. It was this very difficult trajectory to characterize that had led bacteriologists to underestimate the speed of the microorganism. ” The actual speed [de Marinococcus marinus] is not its apparent speed, the spirals considerably increasing the distance traveled“, Explain the researchers. Also, the speed of the bacteria would not be 100 µm / s but 400 to 500 µm / s. Compared to the size of the bacteria of around 1 µm, this speed seems considerable: most known bacterial species with flagella do not travel 400 to 500 times their size every second, but 40 to 50 times their size in one second, the period during which an Olympic champion would advance his size less than once.
This microorganism is also capable of orienting itself in less than 5 milliseconds (5 ms), the study reveals. This extreme speed of movement and reorientation is linked to a distribution and a movement rotary beams of flagella different from what we had imagined. In fact, the groups of flagella of the bacteria are arranged at the two poles of the cell: “Only one movement cooperative understanding where a bundle of flagella grows while the other pulls the cell can explain the observed motility characteristics “, details the study. A sudden change in the direction of rotation of these flagella allows finalized reorientations sometimes in 2.5 ms.
Break down the movement of the bacteria in microscopy assisted by digital tools
“The movement of the fastest microorganisms has notably remained unexplored due to experimental limitations“, Explain the researchers in their study. If they have successfully explained the mobility of Magnetococcus marinus by the synchronized rotation of its flagella, it is because they have set up an analysis method combining new microscopy image recording systems and analysis of these shots using digital simulations of the movement of the microorganism.
In fact, the morphology of the flagellum bundles was first observed by electron microscopy. This confirmed their establishment at the two poles of the cell. However, since electron microscopy required preparing the sample in a way that immobilized it, this technique did not allow the movement of these organelles to be characterized. In order to observe their rotation, the scientists used high intensity dark field video microscopy, which in particular keeps the sample in a state mobile and record images at a rate of 1,424 shots per second. ” Although a state-of-the-art flagella imaging method and a sufficiently high frame rate [[…] have been chosen, the resulting images reveal little information about the exact positions and dynamics of the flagella bundle“, Deplore the researchers in their study: the small size of the cells, their extremely high swimming speed and the strong movement of the flagellum beams made microscopy insufficient to observe the rotation of the beams.
To supplement the microscopy data, the researchers turned to numerical simulations of swimming Magnetococcus marinus. ” We tested different scenarios, [différentes possibilités de configuration de flagelles], and found that a synchronous rotation of the two bundles of flagella was most likely“, Say the authors in the review eLife.
Usefulness of this rapidity for bacteria … and perhaps for humans
Magnetococcus marinus therefore swims extremely quickly. What for ? The answer remains mysterious: no bacteriologist has yet managed to explain the motility of micro-swimmers such as Magnetococcus marinus by scientifically valid demonstrations. However, researchers from the University of Aix Marseille have proposed a hypothesis advanced by the scientific community since the year 2000. Knowing that micro-swimmers and magnetostatic bacteria (capable of orienting themselves according to a magnetic field) such as Magnetococcus marinus are most abundant in sedimentary aquatic environments highly coveted by many species, mobility must be a selective advantage. The ability to move quickly and jump in complex spirals could, for example, allow bacteria to avoid obstacles.
What is certain is that understanding the motility of micro-swimmers has implications ranging from understanding the migration of phytoplankton to that of autonomously acting microbes in medical scenarios, the researchers explain in their study. ” [[Is that] the most common micro-swimmers in our daily lives are bacteria, most of which use flagella for locomotion“, Specify the authors by press release.
Furthermore, the high mobility of these bacteria could find applications in various fields. It could be used in medical micro-robotics. ” It could also be used to remediate areas polluted with petroleum or heavy metals ”, imagine the authors: the bacteria could absorb pollutants, be guided at high speed to predefined areas, sort of landfills, where they would release these toxins.
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We have known for a long time that the bacteria Magnetococcus marinus, present in marine sediments, could advance by swimming at the bottom of theocean. What was less known, however, was the speed at which she could travel.
In partnership with scientists Germans from the Max Planck Institute in Potsdam and the University of Göttingen, a team of French researchers from the Aix-Marseille Institute of Biosciences and Biotechnology therefore examined the trajectory of this microorganism by a method combining observation of the bacteria under the microscope and digital simulation of its movement. The results of these analyzes, presented in a study published by the journal eLife January 28, 2020, indicate that Magnetococcus marinus describes complex spirals at a speed never before observed in a bacteria: it is able, in one second, to travel a distance equivalent to almost 500 times its own size.
If such work makes it possible to specify the morphology of Magnetococcus marinus and to better understand the mobility of so-called “micro-swimmers” microorganisms, they could also find environmental applications or in medical micro-robotics.
A fast bacteria with two flagella
” Bacteria propel and change direction by spinning long helical filaments, called flagella“, Recall the authors of the study in a communicated dated February 25, 2020. These flagella, according to their number, their arrangement around the micro-organism and their direction of rotation, determine, like the engines of a boat, the characteristics of the movement of each species of bacteria. . Other cells than bacteria may have flagella. This is the case, for example, with human sperm, the flagellum of which goes up the female genital tract to the ovum.
We have known for a long time that Magnetococcus marinus, a round bacteria with a diameter of about 1 micrometer, was able to move forward. We had noticed that the trajectory of this bacterium became more complex in the presence of a magnetic field – it is this sensitivity to the magnetic field, linked to the presence of organelles called magnetosomes in the cell, which had given its genus name to the bacterium Magnetococcus marinus. We even called this complex trajectory helical. Therefore, it was thought that Magnetococcus marinus had two groups of flagella all attached to the same hemisphere of the cell, as if the microorganism had two bundles of tails: it was assumed that the bacteria was swimming cell body forward, flagella towards the back to propel the microorganism. In addition, it has been estimated until today that the swimming speed of Magnetococcus marinus at 100 micrometers per second (µm / s).
The work of researchers at the University of Aix-Marseille, however, showed that we were wrong.
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