Researchers from Duke University have uncovered the detailed mechanics of the way fungal spores have evolved to harness the power of merging water droplets to launch in a uniform manner.
Fungal spores grow on the ends of long, thin tethers called sterigmas. Once mature, the spores must break away and be transported to a new location to grow. Some spores rely on animals or their own power to travel. Others—called ballistospores—are actively ejected from the surface of the parent organism. And in the case of some fungi, water droplets provide the liftoff.
More than a century ago, Reginald Buller discovered that a spherical drop of water that forms close to a spore is crucial to the spore’s dispersal. Dubbed the “Buller drop,” its merging with another lens-shaped drop on the spore causes the spore to break away from its tether.
“The spores are launched with a massive amount of force in a specific direction, almost like a cannon,” said Chuan-Hua Chen, associate professor of mechanical engineering and materials science at Duke. “And the ballistospore cannon has evolved to shoot directly away from the fungus to give the spores the best chance of escape.”
While this phenomenon had been explained energetically, the detailed mechanisms—particularly the nearly uniform direction of the spores’ launches—have remained a mystery. In a paper published in the Journal of the Royal Society Interface on July 26, Chen and his colleagues use high-speed cameras and an inkjet printer to solve the riddle.
The major hurdle to uncovering the details of how water droplets launch these spores has been the speed of the action. While it takes several minutes for water droplets to grow large enough for takeoff, the event itself takes less than a microsecond.
“And unfortunately a microsecond is also the time resolution for most high-speed cameras,” Chen said. “So while researchers made some progress in capturing the overall coalescence process, the detailed…