Algae are known to congregate and bloom in massive numbers, covering patches of the ocean in thick red and brown blotches. Some of these “red tide” events create dazzling nighttime light shows of blue-green bioluminescence resulting from the force generated by breaking waves.
While many mysteries remain on how such red tide blooms emerge, marine biologists are now making progress in decoding the mechanisms that trigger bioluminescence.
Marine biologist Michael Latz from Scripps Institution of Oceanography at UC San Diego has been studying bioluminescence for more than 30 years and is now zeroing in on the forces that flick the “on” switch for bioluminescencent flashes in single-celled algae known as dinoflagellates.
Dinoflagellates employ bioluminescence as a defense mechanism. They use the bright flash to ward off potential predators as well as call attention to the predators of their predators as a type of alarm. Evolution has equipped dinoflagellates with an extremely fast response to stimuli, with bioluminescence produced only 15 milliseconds after stimulation.
In a study recently featured on the cover and blog of Biophysical Journal, Latz and former Scripps postdoctoral researcher Benoit Tesson employed a state-of-the-art laboratory instrument called an atomic force microscope to study the force sensitivity of dinoflagellates with unprecedented resolution. They set out to measure the exact forces that trigger light production inside dinoflagellate cells, setting the specifications for the atomic force microscope, in which a calibrated lever was used to apply precisely controlled forces on individual dinoflagellate cells. Such diligence paid off, as the results identified the force conditions that were required to trigger the light. Cells responded to a minimum force of seven micronewtons, which, according to U.S. Navy physicist Jim Rohr, who is familiar with the study, is equivalent to the “weight of an ant resting on your skin.”
Most interesting, the researchers say, was that if the same level of force was applied slowly, there was no response. The difference was due to the mechanical properties of the cells. According to a model they developed, at low stimulation speed the resulting energy was dissipated while at high speed energy was able to build up.
“It is like the difference between pushing and punching; for the same applied force, at high speeds a deformable material acts stiffer and the shock is stronger,” said Tesson.
The results will contribute to the use of dinoflagellate bioluminescence as a tool in engineering and oceanography to visualize flows that are difficult to study otherwise. As Leonardo da Vinci used grass seeds to observe water flow more than 500 years ago, scientists today use bioluminescence to naturally “light up” flow forces associated with jet turbulence, breaking waves, and the swimming movements of dolphins. Knowing the precise trigger point of light emission will aid studies in which bioluminescence is used to study flow forces.
“Cells are sophicated integrators of the forces in their environment,” said Latz. “With these results we further our understanding of how the structural properties of these organisms affect their force sensitivity, and how force sensing evolved, because the system appears to have conserved elements that are used in force sensing by higher organisms, including humans.”
So the next time you see how the red tide sparkles at night, Latz says, you can think of the algae as little force-sensing machines.
The U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative, National Science Foundation, and UC San Diego Academic Senate funded the research. Use of the atomic force microscope was provided by Scripps Oceanography marine biologist Mark Hildebrand.
— Mario C. Aguilera