Learning Thru Research: How Euglena react to the intensity of the magnetic field?

Nicolas Larrouy - Nikola Zaverski - Sarah Talon Sampieri

HOW EUGLENA REACT TO THE INTENSITY OF THE MAGNETIC FIELD?

During the second week of biosensors, we studied how organisms and electronic sensors react to forces.

euglena Gracilis (Euglena gracilis) are eukaryotic organisms living in spring or salt water, and who undergo phototaxis, a property that allow them to move toward or against the light source. Nowadays some studies show they can orientate themselves following the electromagnetic field (magnetotaxis).

We decided then to investigate more on this sensitivity of euglena to react to the magnetic field, asking: “with which precision do they orientate themselves depending on the intensity of the magnetic field?”

As the aim of the week was to compare this biological sensor to an electronic one, we decided to use a magnetic sensor (mpu-9250) (part of the Movuino) to see what were the differences in catching the intensity of the magnetic field.

figure 1: Structure of Euglena. They have an eyespot and a photoreceptor to catch light. It is not clear if they have a specific receptor to catch the magnetic field lines. Source: wikipedia commons

Credits: This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication,

Watch this video if you want to see how Euglena use their flagellum and contract themselves to move!

To evaluate Euglena orientation, we built a setup to hold together two magnets. In that way, putting a slide with Euglena between the magnets and under a microscope would allow us to observe this orientation.

Making research, we found out that Euglena seems to orient itself perpendicularly to the magnetic field: for this reason, we needed to know the direction of the field lines between the magnets before placing our Euglena in these conditions. With some iron dust, we found out the magnetic lines were perpendicular to the position of the two magnets (look at figure 2). Keep in mind that the intensity of the magnetic field is constant because the distance between the magnets is constant!

B.

Image 2: Orientation of iron Dust (fig A), that illustrate how the field lines should look like (Fig.B).

We made 10 replicates, and for our 10 slides, we also took measures used as reference: observing our populations without the magnetic field, in order to compare to the experiments with the magnetic field, and estimate a difference.

Image 3: We considered the orientation of each euglena by seeing what angle was formed between the direction of the euglena and the line of the magnetic field. For the negative control, we looked at this same angle, even if there was no magnetic field, to see if there was a real difference in orientation in the two conditions.

With the same technics, we tested out our Movuino in the same conditions, in order to compare our biological values to our electronic ones.

The distances set for the electronic sensor were 34mm. We measured how effectively the MPU-9250 is able to measure the orientation of magnetic fields. For that we placed the y-axis of the magnetometer in parallel with the field lines.

Image 4 : This is a vector symbolizing the orientation of the magnetic field compared to the orientation of the y-axis. Here you can see that the arrow is pointing in the same direction of the Y-axis. After some calculations, we observed that the angle between the two is near 0°. Conclusion: the magnetometer is really precise at sensing magnetic field’s orientation

After that, we compared our control data (without magnetic field) with our test. It appeared a difference in the mean values between those 2 data, and a statistical test has proven that it was significant. However, we have to be careful, because in both case, the values were far from the mean, what can be explained by the noise we had, conducting the experiments.

The results are interesting because it shows that you can obtain statistically relevant results whereas in reality you cannot conclude. Indeed, while you’re making an experiment, a lot of errors and biases can impact your results. Just to explicit one among many: we had to measure 30 Euglena per picture in order to determine the average orientation but we might, unconsciously, chose the ones that were orientated in a specific way. It is called a bias of measurement. The only thing you can do about that is to acknowledge them and design a follow-up protocol avoiding them.

Anyway, there is a lot to discover about Euglena and their interaction with magnetic fields :)

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