Elysia Chlorotica

Elysia chlorotica is a small-medium-sized green sea slug. It is a member of the genus Sacoglossa, which are sap-sucking sea snails; it is found along the eastern coast of the United States, as far north as Nova Scotia, Canada, and as south as southern Florida. Elysia chlorotica is a species of this type of solar-powered sea snail. It lives in an intracellular endosymbiotic relationship with the chloroplasts of the marine heterokont alga Vaucheria litorea1 .

Figure 1: Elysia Chlorotica – The solar powered half animal, half plant sea slug1.

Feeding

Elysia chloroticas meet their nutritional needs by eating Vaucheria litorea algae. The fry is brown with red pigment spots before feeding. At this point, the animal has no chloroplast. When fed with the algae Vaucheria lithorea, it will turn green by putting the algae chloroplasts into its own intestinal cells2. This is due to the distribution of chloroplasts throughout the widely branched intestine. At first, the slug must constantly feed on algae to keep the chloroplasts down, but over time, the chloroplasts become more committed to intestinal cells, which keeps the snot green without further feeding. Some Elysia chlorotica slugs are even known to be able to use photosynthesis for up to a year after just a few feedings2,3. The chloroplasts of the algae are introduced into the cell through the process of phagocytosis, where sea slug cells engulf the algal cells and make the chloroplasts part of their cellular content4. The incorporation of chloroplasts into the cells of Elysia chlorotica allows the slime to capture energy directly from light through the process of photosynthesis, as most plants do. It can survive for months when algae are not readily available as a food source. This survival was once thought to depend on sugars produced through photosynthesis by chloroplasts, and chloroplasts were found to survive and function for up to nine or even ten months2. Although Elysia chlorotica cannot synthesize its own chloroplasts, its ability to maintain chloroplasts in a functional state may indicate that it has photosynthesis-promoting genes in its nuclear genome, probably through horizontal gene transfer. Because chloroplast DNA alone encodes only 10% of the proteins necessary for proper photosynthesis, the scientists searched the Elysia chlorotica genome for potential genes that could support chloroplast survival and photosynthesis5. The researchers found a vital algal gene, psbO (a nuclear gene encoding a manganese-stabilizing protein in the photosystem II complex). This gene was the same in the sea slug’s DNA as the algal version. They concluded that the gene may have been acquired via horizontal gene transfer, as it was already present in the eggs and sex cells of Elysia chlorotica. Due to the ability to use this horizontal gene transfer, chloroplasts can be used as efficiently as before6,7.

Figure 2: Sea slug has taken genes from algae it eats2.

Life Cycle

It is argued that there are two periods in which sea snails differ from each other summer and winter. These two life cycles are of great importance for the population. The coexistence of two species with different life cycles does not pose a threat to both species8.

Figure 3: The life cycle of the Elysia Chloritica3.

Discussion

According to the researchers, it has been seen that no animal species that can produce energy by photosynthesis like plants has been encountered until now. This discovery raises the issue of artificial photosynthesis. If we can understand how the snail can use these stolen and isolated plastids to produce carbon separately from the plant cell, at the end of the day, we can design green machines and generate bioenergy using isolated plastids.

References:

  1. Blanchet, 2012. “Elysia chlorotica” (On-line), Animal Diversity Web. Accessed October 02, 2022https://animaldiversity.org/accounts/Elysia_chlorotica/
  2. Symbio The Sea Slug-Elysia Chlorotica https://web.archive.org/web/20110831025927/http://sbe.umaine.edu/symbio/3Slug/3feeding.html
  3. Cruz, S., Calado, R., Serôdio, J., & Cartaxana, P. (2013). Crawling leaves: photosynthesis in sacoglossan sea slugs. Journal of experimental botany, 64(13), 3999–4009. https://doi.org/10.1093/jxb/ert197
  4. C V Mujer, D L Andrews, J R Manhart, S K Pierce, M E Rumpho.Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica., (1996) https://www.pnas.org/doi/abs/10.1073/pnas.93.22.12333
  5. Serôdio, J., Cruz, S., Cartaxana, P., & Calado, R. (2014). Photophysiology of kleptoplasts: photosynthetic use of light by chloroplasts living in animal cells. Philosophical transactions of the Royal Society of London. Series B, Biological sciences, 369(1640), 20130242. https://doi.org/10.1098/rstb.2013.0242 https://www.journals.uchicago.edu/doi/10.1086/BBLv223n1p138
  6. Susan P. Devine, Keren P. Pelletreau, Mary E. Rumpho.2012.16S rDNA-Based Metagenomic Analysis of Bacterial Diversity Associated With Two Populations of the Kleptoplastic Sea Slug Elysia chlorotica and Its Algal Prey Vaucheria litorea.The University of Chicago Press Journals. https://www.journals.uchicago.edu/doi/abs/10.1086/BBLv223n1p138
  7. Havurinne, V., & Tyystjärvi, E. (2020). Photosynthetic sea slugs induce protective changes to the light reactions of the chloroplasts they steal from algae. eLife, 9, e57389. https://doi.org/10.7554/eLife.57389
  8. Yamaguchi, S., Yusa, Y., & Iwasa, Y. (2021). Evolution of life cycle dimorphism: An example of sacoglossan sea slugs. Journal of theoretical biology, 525, 110760. https://doi.org/10.1016/j.jtbi.2021.110760

Figure References:

  1. https://plantlet.org/elysia-chlorotica-the-solar-powered-half-animal-half-plant-sea-slug/
  2. https://www.eurekalert.org/news-releases/478953
  3. https://europepmc.org/article/med/21177950

Inspector: Furkan EKER

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