Team:BCCS-Bristol/BSim/Case studies/Magnetotaxis

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(New page: {{:Team:BCCS-Bristol/Header}} = Magnetotaxis = Magnetotactic bacteria are gram-negative, motile (by means of a flagella) bacteria. Each one forms a string of intracellular magnetic gra...)
 
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= Magnetotaxis =
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The video shows magnetotactic bacteria influenced by a magnetic field strength of 7.53x10^(-6) Tesla. The field direction controls the alignment of the bacteria, but not the speed that they travel at. The higher the field direction, the stronger the alignment of the bacteria with the field direction.
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Magnetotactic bacteria are gram-negative, motile (by means of a flagella) bacteria. Each one forms a string of intracellular magnetic grains, known as magnetosomes.
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==Experiment: Effect of magnetic field strength on average velocity of bacteria==
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[[Image:BCCS-Bristol_Magnetosomes.jpg|center|frame|Figure 1: Transmission electron micrograph of Magnetospirillum magnetotacticum showing the magnetosomes inside the bacteria. Bar equals 1 micron.[[#ref1|[1] ]]]]
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Several experiments were carried out on the bacteria. The first was to look at the effect of varying the magnetic field strength on the average velocity of the bacteria. The graph (Figure 1) below shows the result of this. As can be seen, there is a maximum average velocity of the bacteria after which increasing the magnetic field strength has no further effect on the magnetic dipole moment of the bacteria.
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The term magnetotaxis, used to describe the motion of the bacteria in the direction of the magnetic field, denotes the magnetic field effects, solely, on the direction of the bacteria, and not on the speed of the bacteria.  
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[[Image:BCCS-Bristol_VaryingFieldOnVelocity.jpg|center|frame|Figure 1: Graph of the effect of varying the magnetic field strength on the average velocity of the bacteria.]]
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Naturally occurring magnetotactic bacteria will instinctively travel in the direction of the geomagnetic field. It controls the bacteria in the same way as it would control a compass needle, aligning them both to magnetic north pole. [[#ref2|[2]]]
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==Experiment: Magnetotaxis versus chemotaxis==
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Although the magnetic field forces the alignment of the bacteria, they experience no further magnetic force. All of the propulsion is produced from the flagella force.  
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The next experiment was to compare the magnetotactic bacteria with the chemotactic effects on bacteria.
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The shift of the bacteria towards the magnetic field lines is controlled by the strength of the magnetis field and the magnetic moment of the bacteria. The probability of a moment making an angle between theta and some small increment added on to theta is:
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Using a chemical concentration of aspartate, the average velocity of the bacteria is not affected by different concentrations, as the bacteria will only detact a change, not by how much it has changed. Running this simulation for 100 bacteria, it was found that the average velocity of the bacteria was 76.30 microns/second.  
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[[Image:BCCS-Bristol_MagneticEquation.PNG|center]]
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In order to run a simulation with the same average velocity of magnetotactic bacteria instead, the magnetic field strength must be equal to 7.53x10^(-6) Tesla.
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where m = bacteria magnetic moment, B = magnetic field strength, k = Boltzmann constant, T = temperature in Kelvins and where the denominator is the total number of magnetic moments and there is a factor of 2*pi*radius^2 cancelled out.  
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Additionally, the magnetic field strength can still be increased further, thereby increasing the average velocity of magnetotactic bacteria higher than that of chemotactic bacteria.  
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This equation can be used to generate a distribution of the angles that a group of bacteria make with the magnetic field direction. As shown in the graph below [[#ref3|[3] ]]:
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Finally, the ability to control the positions of the bacteria was compared for the two cases. The plots below (Figure 2) show the locations over time of individual bacteria, with magnetotactic bacteria on the left and chemotactic bacteria on the right. Clearly, while the two methods have the same average velocity, the deviation of the magnetotactic bacteria is much smaller. This means that it is easier to predict the location of a particular bacteria and so they are more easily controllable.
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[[Image:BCCS-Bristol_Maxwell-Boltzmann.png|center]]
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[[Image:BCCS-Bristol_MagnetotaxisVsChemotaxis.jpg|center|frame|Figure 2: Plots showing the location of individual bacteria over time in one directional axis. On the left is magnetotactic bacteria and on the right is chemotactic bacteria.]]
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This distribution is known as the Maxwell-Boltzmann distribution. Sampling from this provides a more accurate representation of the motion of the magnetotactic e. coli in BSim.
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While magnetotactic e. coli may be some way off, the desire to work on this can be understood when these experiments can show so clearly the distinct advantage as far as velocity and controllability in the use of magnetotactic bacteria as opposed to chemotactic bacteria.
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BSim allows the user to control the magnetic field strength, B and the magnetic moment, m of the bacteria.
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==References:==
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{{anchor|ref1}}[1] http://www.calpoly.edu/~rfrankel/magbac101.html
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{{anchor|ref2}}[2] Blakemore, RP (1982) Magnetotactic bacteria. Annual Reviews of Microbiology 36: 217-238.
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{{anchor|ref3}}[3] Nicola Ann Spaldin, Magnetic materials: fundamentals and device applications, University Press, Cambridge 2003
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Latest revision as of 01:51, 22 October 2009

BCCS-Bristol
iGEM 2009


The video shows magnetotactic bacteria influenced by a magnetic field strength of 7.53x10^(-6) Tesla. The field direction controls the alignment of the bacteria, but not the speed that they travel at. The higher the field direction, the stronger the alignment of the bacteria with the field direction.

Experiment: Effect of magnetic field strength on average velocity of bacteria

Several experiments were carried out on the bacteria. The first was to look at the effect of varying the magnetic field strength on the average velocity of the bacteria. The graph (Figure 1) below shows the result of this. As can be seen, there is a maximum average velocity of the bacteria after which increasing the magnetic field strength has no further effect on the magnetic dipole moment of the bacteria.

Figure 1: Graph of the effect of varying the magnetic field strength on the average velocity of the bacteria.

Experiment: Magnetotaxis versus chemotaxis

The next experiment was to compare the magnetotactic bacteria with the chemotactic effects on bacteria.

Using a chemical concentration of aspartate, the average velocity of the bacteria is not affected by different concentrations, as the bacteria will only detact a change, not by how much it has changed. Running this simulation for 100 bacteria, it was found that the average velocity of the bacteria was 76.30 microns/second.

In order to run a simulation with the same average velocity of magnetotactic bacteria instead, the magnetic field strength must be equal to 7.53x10^(-6) Tesla.

Additionally, the magnetic field strength can still be increased further, thereby increasing the average velocity of magnetotactic bacteria higher than that of chemotactic bacteria.

Finally, the ability to control the positions of the bacteria was compared for the two cases. The plots below (Figure 2) show the locations over time of individual bacteria, with magnetotactic bacteria on the left and chemotactic bacteria on the right. Clearly, while the two methods have the same average velocity, the deviation of the magnetotactic bacteria is much smaller. This means that it is easier to predict the location of a particular bacteria and so they are more easily controllable.

Figure 2: Plots showing the location of individual bacteria over time in one directional axis. On the left is magnetotactic bacteria and on the right is chemotactic bacteria.

While magnetotactic e. coli may be some way off, the desire to work on this can be understood when these experiments can show so clearly the distinct advantage as far as velocity and controllability in the use of magnetotactic bacteria as opposed to chemotactic bacteria.

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