Marine Luminescence Appears After Stress Test

DOUGLAS FARMER, SENIOR EDITOR
doug.farmer@photonics.com

No matter how small, organisms respond to their surrounding environment. A group of scientists at the University of Cambridge has shown that the light produced by ocean organisms is related to the stress their cells are under at the time.

The team, led by professor Raymond Goldstein of the university’s Department of Applied Mathematics and Theoretical Physics, wanted to see how such organisms would respond to threats analogous to a predator or the pressure of a wave. The scientists modeled much of their research on work done by Michael Latz and his colleagues at the Scripps Institution of Oceanography at the University of California, San Diego.

In their published study, the researchers reported they held controlled experiments using high-speed imaging to monitor how stress level affects light production at the single-cell level. They used micropipettes (instruments to transport small amounts of liquid) to subject cells of Pyrocystis lunula (a dinoflagellate, or single-celled plankton measuring 30 to 1000 µm) to fluid flow and deformation of the cellular walls.

“We used two different cameras for different aspects of the experiments,” Goldstein said. “For the main imaging it was a Prime 95B sCMOS camera from Photometrics, while for quantification of the flow it was a Phantom V311 from Vision Research. Both are off the shelf.”

The dinoflagellate P. lunula in brightfield illumination. Courtesy of M. Jalaal/University of Cambridge.

The light energy within the cell is caused by fluctuations in calcium levels, which open up voltage-sensitive channels and ultimately create a reaction in the protein luciferin, releasing blue-green light commonly seen in the depths of the ocean.

Scientists in Goldstein’s group discovered that the intensity of the light — which appeared near the nucleus of the largely transparent cells — depended proportionally on the stress, and resulting deformation, that the cells were under at the time. They reasoned this could have great significance in examining the phenomenon of bioluminescence in the sea itself.

“Long before our work, various observations have led to the idea that bioluminescence can serve various purposes in the ecology of the organisms,” Goldstein said. “One of them is a kind of burglar alarm whereby if a predator of the dinoflagellates disturbs the water then the light can signal to predators of the predator to attack … our work does show that the response mechanism acts as a kind of filter to prevent light production (which is energetically costly) when disturbances are small and slow.”

The research was published in Physics Review Letters (www.doi.org/10.1103/PhysRevLett.125.028102).