Magnetic field platform for experiments on well-mixed and spatially structured microbial populations

Magnetic fields have been shown to affect sensing, migration, and navigation in living organisms. However, the effects of magnetic fields on microorganisms largely remain to be elucidated. We develop an open-source, 3D-printed magnetic field exposure device to perform experiments on well-mixed and spatially structured microbial populations. This device is designed in AutoCAD, modeled in COMSOL, and validated using a Gaussmeter and experiments on the budding yeast Saccharomyces cerevisiae. We find that static magnetic field exposure slows the spatially structured expansion of yeast mats that expand in two dimensions, but not yeast mats that expand in three dimensions, across the surface of semi-solid yeast extract-peptone-dextrose agar media. We also find that magnetic fields do not affect the growth of planktonic yeast cells in well-mixed liquid yeast extract-peptone-dextrose media. This study provides an adaptable device for performing controlled magnetic field experiments on microbes and advances our understanding of the effects of magnetic fields on fungi.

See main text for details on days over which fits were performed.The following statistics were used to evaluate the goodness of fit for the data in Tables S2-S5.The SSE -sum of squares due to error:

Parameters Curve Fit
R 2 -ratio between the sum of squares of the regression (SSR) and the total sum of squares (SST ): AdjR 2 -degrees of freedom adjusted R 2 : ; and RM SE -root mean squared error: For the above equations, y i is the i th value of the variable to be predicted, ŷi the predicted value of y i , ȳ the mean of all values of y i , n the number of data points, ν the number of number of degrees of freedom, and (ν = n − m), where m is the number of fitted coefficients estimated from the data points.

Figure S1 :
Figure S1: Modular design of the magnetic field exposure device.(A) AutoCAD [2] image of the disassembled vertical magnetic field (MF) configuration of the device.(B) AutoCAD image of the disassembled horizontal MF configuration of the device.(C) Assembled AutoCAD image of the vertical MF configuration of the device.(D) Assembled AutoCAD image of the horizontal MF configuration of the device.The magnets are depicted in red, magnet holders in yellow, Petri dish holders in cyan, Petri dishes in orange, and the yokes (parts that hold the device together after assembly) in green.

Figure S2 :Figure S3 :Figure S4 :Figure S5 :
Figure S2: Experimental setup to map the magnetic flux density ( ⃗ B). (A) AutoCAD [2] image of the cylindrical device with 83 rectangular holes used to hold the Gaussmeter probe during ⃗ B measurements.(B) Schematic of three different layers in which ⃗ B was mapped using the Gaussmeter.The grey blocks denote the permanent magnets and the Petri dishes are shown in blue.The red line indicate the layers that were evaluated in the ⃗ B mapping.

Figure S6 :
Figure S6: Difference between simulated and experimental magnetic flux densities of horizontal configuration of the magnetic field device for layer 3. The point of view for this figure is from the top view of the middle layer (layer 3).(A) The difference between the simulated and measured magnetic flux densities ( ⃗ B).Values of ⃗ B are in Gauss (G).(B) The difference between the simulated and experimentally measured ⃗ B values as a percentage of the experimental values.

Figure S7 :
Figure S7: Representative images of the development of TBR1 yeast mats for (Top) the horizontal MF exposed condition and for (Bottom) the control condition (no MF).

Figure S8 :
Figure S8: Representative images of the development of TBR1 yeast mats for (Top) the vertical MF exposed condition and for (Bottom) the control condition (no MF).

Figure S9 :
Figure S9: Representative images of the development of TBR5 yeast mats for (Top) the horizontal MF exposed condition and for (Bottom) the control condition (no MF).

Figure S10 :
Figure S10: Representative images of the development of TBR5 yeast mats for (Top) the vertical MF exposed condition and for (Bottom) the control condition (no MF).

Table S2 :
Goodness of fit of the average area expansion rate data for TBR1-TBR5 control (no MF) and experimental (MF) group data for the horizontal MF experiments.The model (linear, exponential, and logarithmic) with the best goodness of fit statistic are highlighted in green for TBR1 and yellow for TBR5.

Table S3 :
Goodness of fit of the average area expansion rate data for TBR1-TBR5 control (no MF) and experimental (MF) group data for vertical MF experiments.The model (linear, exponential, and logarithmic) with the best goodness of fit statistic are highlighted in green for TBR1 and yellow for TBR5.See main text for details on days over which fits were performed.
TableS5: Goodness of fit of average area data for TBR1-TBR5 control (no MF) and experimental (MF) group data for the vertical MF experiments.The model (linear, exponential, and logarithmic) with the best goodness of fit statistic are highlighted in green for TBR1 and yellow for TBR5.See main text for details on days over which fits were performed.