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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. Latz^1,*, Michelle Bovard^1,, Virginia VanDelinder^2,, Enrico Segre³, Jim Rohr^1,4 and Alex Groisman^2,*

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

^* Authors for correspondence (e-mails: mlatz{at}ucsd.edu; agroisman{at}ucsd.edu)

Accepted 26 June 2008

Dinoflagellate bioluminescence serves as a model system for examining mechanosensing by suspended motile unicellular organisms. The response latency, i.e. the delay time between the mechanical stimulus and luminescent response, provides information about the mechanotransduction and signaling process, and must be accurately known for dinoflagellate bioluminescence to be used as a flow visualization tool. This study used a novel microfluidic device to measure the response latency of a large number of individual dinoflagellates with a resolution of a few milliseconds. Suspended cells of several dinoflagellate species approximately 35 µm in diameter were directed through a 200 µm deep channel to a barrier with a 15 µm clearance impassable to the cells. Bioluminescence was stimulated when cells encountered the barrier and experienced an abrupt increase in hydrodynamic drag, and was imaged using high numerical aperture optics and a high-speed low-light video system. The average response latency for Lingulodinium polyedrum strain HJ was 15 ms (N>300 cells) at the three highest flow rates tested, with a minimum latency of 12 ms. Cells produced multiple flashes with an interval as short as 5 ms between individual flashes, suggesting that repeat stimulation involved a subset of the entire intracellular signaling pathway. The mean response latency for the dinoflagellates Pyrodinium bahamense, Alexandrium monilatum and older and newer isolates of L. polyedrum ranged from 15 to 22 ms, similar to the latencies previously determined for larger dinoflagellates with different morphologies, possibly reflecting optimization of dinoflagellate bioluminescence as a rapid anti-predation behavior.

Key words: bioluminescence, Alexandrium, dinoflagellate, flash, latency, Lingulodinium, microfluidic, Pyrodinium

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