Just as plants and animals on land are keenly attuned to the hours of sunlight in the day, life in the oceans follows the rhythms of the day, the seasons and even the moon. A 天美影院 study finds the biological light switches that make this possible.
Single-celled organisms in the open ocean use a diverse array of genetic tools to detect light, even in tiny amounts, and respond, according to a study published the week of Feb. 1 in the Proceedings of the National Academy of Sciences.
鈥淚f you look in the ocean environment, all these different organisms have this day-night cycle. They are very in tune with each other, even as they get moved around. How do they know when it鈥檚 day? How do they know when it鈥檚 night?鈥� said lead author , a research scientist in oceanography at the UW.
Though invisible to the human eye, ocean microbes support all marine life, from sardines to whales. Knowing these communities鈥� inner workings could reveal how they will fare under changing ocean conditions.
鈥淛ust like rainforests generate oxygen and take up carbon dioxide, ocean organisms do the same thing in the world鈥檚 oceans. People probably don鈥檛 realize this, but these unicellular organisms are about as important as rainforests for our planet鈥檚 functioning,鈥� Coesel said.
By analyzing RNA filtered out of seawater samples collected throughout the day and night, the study identifies four main groups of photoreceptors, many of them new. This genetic activity uses light to trigger changes in the metabolism, growth, cell division, movements and death of marine organisms.
The discovery of these new genetic 鈥渓ight switches鈥� could also aid in the field of , in which a cell鈥檚 function can be controlled with light exposure. Today鈥檚 optogenetic tools are engineered by humans, but versions from nature might be more sensitive or better detect light of particular wavelengths, the researchers said.
鈥淭his work dramatically expanded the number of photoreceptors 鈥� the different kinds of those on-off switches 鈥� that we know of,鈥� said senior author , a 天美影院professor of oceanography.
Not surprisingly, many of the new tools were for light in the blue range, since water filters out red wavelengths (which is why oceans appear blue). Some were also for green light, Coesel said.
The researchers collected water samples far from shore and looked at all genetic activity from protists: single-celled organisms with a nucleus. They filtered the water to select organisms measuring between 200 nanometers to one-tenth of a millimeter across. These included photosynthetic organisms, like algae, which absorb light for energy, as well as other single-celled plankton that gain energy by consuming other organisms.
The team collected samples every four hours, day and night, for four days in the North Pacific near Hawaii. Researchers used trackers to follow the currents about 15 meters (50 feet) below the surface so that the samples came from the same water mass.
The study also looked at samples that came from a depth of 120 and 150 meters (400 and 500 feet), in the ocean鈥檚 鈥渢wilight zone.鈥� Even there, the genetic activity showed that the organisms were responding to very low levels of sunlight.
While the sun is up, these organisms gain energy and grow in size, and at night, when the ultraviolet light is less damaging to their DNA, they undergo cell division.
鈥淒aylight is important for ocean organisms, we know that, we take it for granted. But to see the rhythm of genetic activity during these four days, and the beautiful synchronicity, you realize just how powerful light is,鈥� Armbrust said.
Future work will look at places farther from the equator, where plankton communities are more subjected to the changing seasons.
This research was funded by the Simons Foundation and the National Science Foundation鈥檚 Extreme Science and Engineering Discovery Environment program. Other co-authors are Ryan Groussman, Rhonda Morales and Fran莽ois Ribalet at the UW; Bryndan Durham at the University of Florida; Sarah Hu at Woods Hole Oceanographic Institution; and David Caron at the University of Southern California.
For more information, contact Coesel at coesel@uw.edu or Armbrust at armbrust@uw.edu.