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First published online August 14, 2009
Journal of Experimental Biology 212, 2835-2843 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.029975
Surface tension propulsion of fungal spores
1 Laboratoire de Physique de la Matière Condensée, CNRS–UMR
6622, Université de Nice-Sophia-Antipolis, Parc Valrose, 06108 Nice,
Cedex 2, France
2 Department of Biology, University of Washington, Seattle, WA 98195, USA
3 Department of Organismic and Evolutionary Biology, Harvard University,
Cambridge, MA 02138, USA
* Author for correspondence (jdumais{at}oeb.harvard.edu)
Accepted 6 June 2009
Most basidiomycete fungi actively eject their spores. The process begins
with the condensation of a water droplet at the base of the spore. The fusion
of the droplet onto the spore creates a momentum that propels the spore
forward. The use of surface tension for spore ejection offers a new paradigm
to perform work at small length scales. However, this mechanism of force
generation remains poorly understood. To elucidate how fungal spores make
effective use of surface tension, we performed a detailed mechanical analysis
of the three stages of spore ejection: the transfer of energy from the drop to
the spore, the work of fracture required to release the spore from its
supporting structure and the kinetic energy of the spore after ejection.
High-speed video imaging of spore ejection in Auricularia auricula
and Sporobolomyces yeasts revealed that drop coalescence takes place
over a short distance (
5 µm) and energy transfer is completed in less
than 4 µs. Based on these observations, we developed an explicit relation
for the conversion of surface energy into kinetic energy during the
coalescence process. The relation was validated with a simple artificial
system and shown to predict the initial spore velocity accurately (predicted
velocity: 1.2 m s–1; observed velocity: 0.8 m
s–1 for A. auricula). Using calibrated
microcantilevers, we also demonstrate that the work required to detach the
spore from the supporting sterigma represents only a small fraction of the
total energy available for spore ejection. Finally, our observations of this
unique discharge mechanism reveal a surprising similarity with the mechanics
of jumping in animals.
Key words: Auricularia auricula, ballistospores, wetting phenomena, spore dispersal, surface tension
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  K. Knight FUNGI OPT FOR WATER POWERED BALLISTICS J. Exp. Biol., September 1, 2009; 212(17): i - ii. [Full Text] [PDF]
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