Researchers found previously undiscovered receptors to sense and respond to light providing new insights on how marine organisms remain attuned to the day and night cycles.
In the same way plants and animals on land adjust their activities based on the presence or absence of sunlight, marine organisms follow the same cycle in addition to the phases of the moon or the seasons. Researchers found that even single-celled organisms in the open ocean use different genetic tools that detect even the faintest shred of light under the water, with details of the study published in the National Academy of Sciences Proceedings, February 1.
Following the Same Day-Night Cycle, Even in the Ocean Depths
"If you look in the ocean environment, all these different organisms have this day-night cycle," began Sacha Coesel, lead author of the study and an oceanography research scientist at the University of Washington, in a UW news release. "They are very in tune with each other, even as they get moved around. How do they know when it's day? How do they know when it's night?"
Ocean microbes form the base that supports large parts of the marine food chain, despite being mostly invisible to the human eye. Researchers note that understanding how these organisms respond and thrive could also provide insights into how they react to changing ocean conditions.
Coesel explains that in the same nature as rainforests take in carbon dioxide and release oxygen, ocean organisms also do a similar thing across the oceans. "People probably don't realize this, but these unicellular organisms are about as important as rainforests for our planet's functioning," she added.
Researchers analyzed minute RNA samples found from collected seawater samples that were gathered across various times - day and night - and identified four main groups of mostly previously undiscovered photoreceptors. They also identified that the genetic activity in these ocean microbes uses light, even in small amounts, to trigger and control different aspects of marine organism's life and function - metabolism, growth, movement, cell division, and more.
They were able to monitor genetic activities by filtering the water to find organisms ranging from 200 nanometers to hundreds of micrometers across. Ocean microbes observed included algae and single-celled plankton.
Finding New Sensory Receptors in Ocean Microbes
The new photoreceptors, or the microorganism's light switches, could also help advance the field of optogenetics: the field of study that focuses on the use of light to control sensory cells. While most existing optogenetic tools are engineered and fabricated by humans, scientific advances have often taken inspiration from nature, whose designs often optimize form and function.
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"This work dramatically expanded the number of photoreceptors-the different kinds of those on-off switches-that we know of," said Virginia Armbrust, senior author of the study and a UW oceanography professor.
Since water filters out red wavelengths of light - making the ocean appear blue - researchers noted that most of the new light receptors were sensitive to the blue light, with others responding to green lights instead.
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