After years of research scientists have discovered a sea slug which is able to integrate genes from the algae it ingests and use them to perform photosynthetic processes, similar to a plant. The emerald green sea slug, Elysia chlorotica, is able to photosynthesize using the algal genes and can survive for months solely on energy produced from this process.
Sidney K. Pierce a member of the research team from the University of South Florida says; “There is no way on earth that genes from an alga should work inside an animal cell, and yet here, they do. They allow the animal to rely on sunshine for its nutrition. So if something happens to their food source, they have a way of not starving to death until they find more algae to eat.” It has been known for decades that the emerald sea slug has taken chloroplasts, which are the organelles responsible for photosynthesis in plants and algae, from the yellow-green algae, Vaucheria litorea, it eats. This process, termed ‘kleptoplasty’ apparently does not harm the chloroplasts but allows them to continue functioning within the cells of the sea slugs for up to 9 months. The photosynthesizing slugs produce lipids as a by-product when sun energy is combined with carbon dioxide giving it the required nourishment with no additional nutrient ingestion required.
Identifying exactly how the slugs manage this process is complex and still unanswered in spite of an experiment performed at the University of Dusseldorf in Germany in 2013. The German research team drugged their slugs with a substance that halted photosynthesis, yet slugs still lived for 55 days. They were a bit smaller and paler but apparently the organelles were still working. Ferris Jabr, contributing writer for Scientific American explains why this is such a conundrum; “In order to photosynthesise, the chloroplasts inside an alga depend on many genes in the alga’s own nucleus and the proteins for which they code. Tearing chloroplasts out of algal cells and asking them to make food inside a slug’s gut is like expecting the bottom half of a blender to puree some carrots sans the blade and glass jar.” So, on what are the chloroplasts dependant on within the slug?
Pierce and his research team decided to attack this problem. The team inserted fluorescent DNA markers which track algal genes as they make their way into the genetic material of the sea slugs. And for the first time ever, the team viewed these genes produce an enzyme vital to proper photosynthetic functioning. This confirms that one of several algal genes needed to repair damage to chloroplasts, and keep them functioning, is also present on the slug chromosome as Pierce confirms; “The gene is incorporated into the slug chromosome and transmitted to the next generation of slugs.”
It is this type of interspecies gene transfer that is the goal of gene therapies being pursued to correct human genetic diseases. While it is exciting to see this process can be successful, sea slugs are not the optimal model for developing medical treatments for humans; their biology is very dissimilar to ours. However, this exceedingly efficient gene transfer mechanism will continue to be studied and used to model other possible medical applications.