In an astonishing achievement akin to adding solar panels to your body, a new study has found that Northeast sea slugs can extract raw materials from algae to provide a lifetime supply of solar-powered energy.
"It's a remarkable feat because it's highly unusual for an animal to behave like a plant and survive solely on photosynthesis," said Debashish Bhattacharya, senior author of the study and distinguished professor in the Department of Biochemistry and Microbiology at Rutgers-New Brunswick.
The sea slug Elysia chlorotica is found in the intertidal zone between Nova Scotia, Canada, and Martha's Vineyard, Massachusetts, as well as in Florida. Juvenile sea slugs eat the nontoxic brown alga Vaucheria litorea. According to the study published in the journal Molecular Biology and Evolution, after stealing millions of algal plastids and storing them in their gut lining, the slugs become photosynthetic.
This particular alga is an ideal food source because it does not have walls between adjoining cells in its body and is essentially a long tube loaded with nuclei and plastids, said Bhattacharya. "When the sea slug makes a hole in the outer cell wall, it can suck out the cell contents and gather all of the algal plastids at once."
This microscopic image shows stolen algal plastids (in green) and lipids from algae (in yellow) inside the sea slug's digestive system. Credit: Karen N. Pelletreau/University of Maine
Based on studies of other sea slugs, some scientists had argued that they steal and store plastids as food to be digested during hard times, like camels that store fat in their humps. This study suggests that is not the case for ‘solar-powered’ Elysia chlorotica, said Bhattacharya
"It has this remarkable ability to steal these algal plastids, stop feeding and survive off the photosynthesis from the algae for the next six to eight months," he said.
The team of Rutgers and other scientists used RNA sequencing (gene expression) to test their solar energy supply hypothesis. The data shows that the slug responds actively to the stolen plastids by protecting them from digestion and turning on animal genes to utilize the algal photosynthetic products. Their findings mirror those found in corals that maintain the dinoflagellates - as intact cells - in symbiotic relationships.
Although Elysia chlorotica stores plastids, the algal nuclei do not survive. Bhattacharya said that scientists still don't know how the sea slug maintains the plastids and photosynthesis for months without the nuclei that are typically needed to control their function.
Bhattacharya explains, "The broader implication is in the field of artificial photosynthesis. That is, if we can figure out how the slug maintains stolen, isolated plastids to fix carbon without the plant nucleus, then maybe we can also harness isolated plastids for eternity as green machines to create bioproducts or energy. The existing paradigm is that to make green energy, we need the plant or alga to run the photosynthetic organelle, but the slug shows us that this does not have to be the case."
Funder: National Science Foundation, Australian Research Council Discovery Project