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First published online August 22, 2008
Journal of Experimental Biology 211, 2865-2875 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.011890
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Bioluminescent response of individual dinoflagellate cells to hydrodynamic stress measured with millisecond resolution in a microfluidic device

Michael I. Latz1,*, Michelle Bovard1,{dagger}, Virginia VanDelinder2,{dagger}, Enrico Segre3, Jim Rohr1,4 and Alex Groisman2,*

1 Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0202, USA
2 Department of Physics, University of California San Diego, La Jolla, CA 92093, USA
3 Department of Physics Services, Weizmann Institute of Science, Rehovot, 76100 Israel
4 SPAWAR Systems Center San Diego, 53560 Hull Street, San Diego, CA 92152, USA


Figure 1
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  		Fig. 1. The microfluidic device. (A) Microfluidic device and portion of connected tubing, shown with a dime for scale (17.91 mm in diameter). (B) Drawing of microchannels in the device. (C) Micrograph of test region, showing flow channels and barrier. Solid arrows indicate direction of flow in the device during its normal operation. Dashed arrow shows flow in channel 5 during the removal of cells from the barrier. Dashed lines mark the boundaries between streams from channels 2, 1 and 3. (D) Schematic three-dimensional drawing of barrier and cells (not to scale). Curved dashed lines are flow lines with arrows indicating flow direction. B and C are rotated 90 deg. counterclockwise with respect to A and D, as indicated by the orientation of the x- and y-axis shown in the panels.

 

Figure 2
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  		Fig. 2. Numerical simulations. (A) Three-dimensional schematic drawing of the segment of channel 4 used in the numeric simulations with a motionless sphere at the barrier. The mesh used in the simulations is shown by thin lines. (B) Two-dimensional cross-section of the channel in the xz-plane of symmetry (vertical midplane) with a freely moving sphere at (–30, 0, 30) µm from the rest position. Curved lines are the streamlines with the flow directed from left to right. Double-headed arrow shows the principal axis of tensile forces exerted at the sphere by the hydrodynamic stresses. Note the minimal bending of the streamlines in the vicinity of the sphere, as the sphere is moving together with the fluid.

 

Figure 3
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  		Fig. 3. Sequence of video frames of a single cell of Lingulodinium polyedrum strain HJ approaching the barrier (dark horizontal line near the bottom). Flow direction is from top to bottom. Frames were taken with an interval of 4 ms; the numbers at the top of each panel show elapsed time in milliseconds. The cell arrived at the barrier at 12 ms and the flash started at 24 ms, resulting in a latency of 12 ms. Scale bar, 50 µm.

 

Figure 4
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  		Fig. 4. Frequency distribution of response latency for Lingulodinium polyedrum strain HJ. (A) Response latency for the experiment with the lowest flow velocity of vmax=5.7mms–1. (B) Response latency for the experiment with a flow velocity of vmax=11 mm s–1. (C) Response latency for the experiments with the highest flow velocities (vmax=15, 35 and 61 mm s–1). Bin width is 10 ms between 0 and 100 ms latency and 100 ms between 100 and 600 ms latency.

 

Figure 5
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  		Fig. 5. Response latency of Lingulodinium polyedrum strain HJ as a function of flow velocity, vmax. Values represent the mean response latency (filled circles) and the minimum response latency (open circles). The y-axis error bars are s.d. of the response latencies, and the x-axis error bars are uncertainties of the flow velocity measurements.

 

Figure 6
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  		Fig. 6. Multiple flashes from individual cells of Lingulodinium polyedrum strain HJ. Data were collected for cells that flashed three or four times at vmax=5.7, 11 and 15 mm s–1. (A) Duration of each flash as a function of flash number. Values are means ± s.d. (N=98 for flashes one to three; N=11 for flash four). (B) Length of interval between consecutive flashes. Values are means ± s.d. (N=98 for the intervals between the first and second and between the second and third flashes; N=11 for the interval between the third and fourth flashes).

 

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© The Company of Biologists Ltd 2008